1
Fork 0
mirror of https://git.savannah.gnu.org/git/guile.git synced 2025-04-30 11:50:28 +02:00
guile/module/system/vm/assembler.scm
Andy Wingo 4cbe4d72aa Fix rtl tests
* module/system/vm/assembler.scm (write-arities): Add a diagnostic.

* test-suite/tests/rtl.test: Fix tests to emit "definition"
  instructions.
2014-04-15 22:00:30 +02:00

2086 lines
80 KiB
Scheme
Raw Blame History

This file contains invisible Unicode characters

This file contains invisible Unicode characters that are indistinguishable to humans but may be processed differently by a computer. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

;;; Guile bytecode assembler
;;; Copyright (C) 2001, 2009, 2010, 2012, 2013, 2014 Free Software Foundation, Inc.
;;;
;;; This library is free software; you can redistribute it and/or
;;; modify it under the terms of the GNU Lesser General Public
;;; License as published by the Free Software Foundation; either
;;; version 3 of the License, or (at your option) any later version.
;;;
;;; This library is distributed in the hope that it will be useful,
;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;;; Lesser General Public License for more details.
;;;
;;; You should have received a copy of the GNU Lesser General Public
;;; License along with this library; if not, write to the Free Software
;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
;;; Commentary:
;;;
;;; This module implements an assembler that creates an ELF image from
;;; bytecode assembly and macro-assembly. The input can be given in
;;; s-expression form, like ((OP ARG ...) ...). Internally there is a
;;; procedural interface, the emit-OP procedures, but that is not
;;; currently exported.
;;;
;;; "Primitive instructions" correspond to VM operations. Assemblers
;;; for primitive instructions are generated programmatically from
;;; (instruction-list), which itself is derived from the VM sources.
;;; There are also "macro-instructions" like "label" or "load-constant"
;;; that expand to 0 or more primitive instructions.
;;;
;;; The assembler also handles some higher-level tasks, like creating
;;; the symbol table, other metadata sections, creating a constant table
;;; for the whole compilation unit, and writing the dynamic section of
;;; the ELF file along with the appropriate initialization routines.
;;;
;;; Most compilers will want to use the trio of make-assembler,
;;; emit-text, and link-assembly. That will result in the creation of
;;; an ELF image as a bytevector, which can then be loaded using
;;; load-thunk-from-memory, or written to disk as a .go file.
;;;
;;; Code:
(define-module (system vm assembler)
#:use-module (system base target)
#:use-module (system vm dwarf)
#:use-module (system vm elf)
#:use-module (system vm linker)
#:use-module (language bytecode)
#:use-module (rnrs bytevectors)
#:use-module (ice-9 binary-ports)
#:use-module (ice-9 vlist)
#:use-module (ice-9 match)
#:use-module (srfi srfi-1)
#:use-module (srfi srfi-4)
#:use-module (srfi srfi-9)
#:use-module (srfi srfi-11)
#:export (make-assembler
emit-text
link-assembly))
;;; Bytecode consists of 32-bit units, often subdivided in some way.
;;; These helpers create one 32-bit unit from multiple components.
(define-inlinable (pack-u8-u24 x y)
(unless (<= 0 x 255)
(error "out of range" x))
(logior x (ash y 8)))
(define-inlinable (pack-u8-s24 x y)
(unless (<= 0 x 255)
(error "out of range" x))
(logior x (ash (cond
((< 0 (- y) #x800000)
(+ y #x1000000))
((<= 0 y #xffffff)
y)
(else (error "out of range" y)))
8)))
(define-inlinable (pack-u1-u7-u24 x y z)
(unless (<= 0 x 1)
(error "out of range" x))
(unless (<= 0 y 127)
(error "out of range" y))
(logior x (ash y 1) (ash z 8)))
(define-inlinable (pack-u8-u12-u12 x y z)
(unless (<= 0 x 255)
(error "out of range" x))
(unless (<= 0 y 4095)
(error "out of range" y))
(logior x (ash y 8) (ash z 20)))
(define-inlinable (pack-u8-u8-u16 x y z)
(unless (<= 0 x 255)
(error "out of range" x))
(unless (<= 0 y 255)
(error "out of range" y))
(logior x (ash y 8) (ash z 16)))
(define-inlinable (pack-u8-u8-u8-u8 x y z w)
(unless (<= 0 x 255)
(error "out of range" x))
(unless (<= 0 y 255)
(error "out of range" y))
(unless (<= 0 z 255)
(error "out of range" z))
(logior x (ash y 8) (ash z 16) (ash w 24)))
(define-syntax pack-flags
(syntax-rules ()
;; Add clauses as needed.
((pack-flags f1 f2) (logior (if f1 (ash 1 0) 0)
(if f2 (ash 2 0) 0)))))
;;; Helpers to read and write 32-bit units in a buffer.
(define-syntax-rule (u32-ref buf n)
(bytevector-u32-native-ref buf (* n 4)))
(define-syntax-rule (u32-set! buf n val)
(bytevector-u32-native-set! buf (* n 4) val))
(define-syntax-rule (s32-ref buf n)
(bytevector-s32-native-ref buf (* n 4)))
(define-syntax-rule (s32-set! buf n val)
(bytevector-s32-native-set! buf (* n 4) val))
;;; A <meta> entry collects metadata for one procedure. Procedures are
;;; written as contiguous ranges of bytecode.
;;;
(define-syntax-rule (assert-match arg pattern kind)
(let ((x arg))
(unless (match x (pattern #t) (_ #f))
(error (string-append "expected " kind) x))))
(define-record-type <meta>
(%make-meta label properties low-pc high-pc arities)
meta?
(label meta-label)
(properties meta-properties set-meta-properties!)
(low-pc meta-low-pc)
(high-pc meta-high-pc set-meta-high-pc!)
(arities meta-arities set-meta-arities!))
(define (make-meta label properties low-pc)
(assert-match label (or (? exact-integer?) (? symbol?)) "symbol")
(assert-match properties (((? symbol?) . _) ...) "alist with symbolic keys")
(%make-meta label properties low-pc #f '()))
(define (meta-name meta)
(assq-ref (meta-properties meta) 'name))
;; Metadata for one <lambda-case>.
(define-record-type <arity>
(make-arity req opt rest kw-indices allow-other-keys?
low-pc high-pc definitions)
arity?
(req arity-req)
(opt arity-opt)
(rest arity-rest)
(kw-indices arity-kw-indices)
(allow-other-keys? arity-allow-other-keys?)
(low-pc arity-low-pc)
(high-pc arity-high-pc set-arity-high-pc!)
(definitions arity-definitions set-arity-definitions!))
(define-syntax *block-size* (identifier-syntax 32))
;;; An assembler collects all of the words emitted during assembly, and
;;; also maintains ancillary information such as the constant table, a
;;; relocation list, and so on.
;;;
;;; Bytecode consists of 32-bit units. We emit bytecode using native
;;; endianness. If we're targeting a foreign endianness, we byte-swap
;;; the bytevector as a whole instead of conditionalizing each access.
;;;
(define-record-type <asm>
(make-asm cur idx start prev written
labels relocs
word-size endianness
constants inits
shstrtab next-section-number
meta sources
dead-slot-maps)
asm?
;; We write bytecode into what is logically a growable vector,
;; implemented as a list of blocks. asm-cur is the current block, and
;; asm-idx is the current index into that block, in 32-bit units.
;;
(cur asm-cur set-asm-cur!)
(idx asm-idx set-asm-idx!)
;; asm-start is an absolute position, indicating the offset of the
;; beginning of an instruction (in u32 units). It is updated after
;; writing all the words for one primitive instruction. It models the
;; position of the instruction pointer during execution, given that
;; the VM updates the IP only at the end of executing the instruction,
;; and is thus useful for computing offsets between two points in a
;; program.
;;
(start asm-start set-asm-start!)
;; The list of previously written blocks.
;;
(prev asm-prev set-asm-prev!)
;; The number of u32 words written in asm-prev, which is the same as
;; the offset of the current block.
;;
(written asm-written set-asm-written!)
;; An alist of symbol -> position pairs, indicating the labels defined
;; in this compilation unit.
;;
(labels asm-labels set-asm-labels!)
;; A list of relocations needed by the program text. We use an
;; internal representation for relocations, and handle textualn
;; relative relocations in the assembler. Other kinds of relocations
;; are later reified as linker relocations and resolved by the linker.
;;
(relocs asm-relocs set-asm-relocs!)
;; Target information.
;;
(word-size asm-word-size)
(endianness asm-endianness)
;; The constant table, as a vhash of object -> label. All constants
;; get de-duplicated and written into separate sections -- either the
;; .rodata section, for read-only data, or .data, for constants that
;; need initialization at load-time (like symbols). Constants can
;; depend on other constants (e.g. a symbol depending on a stringbuf),
;; so order in this table is important.
;;
(constants asm-constants set-asm-constants!)
;; A list of instructions needed to initialize the constants. Will
;; run in a thunk with 2 local variables.
;;
(inits asm-inits set-asm-inits!)
;; The shstrtab, for section names.
;;
(shstrtab asm-shstrtab set-asm-shstrtab!)
;; The section number for the next section to be written.
;;
(next-section-number asm-next-section-number set-asm-next-section-number!)
;; A list of <meta>, corresponding to procedure metadata.
;;
(meta asm-meta set-asm-meta!)
;; A list of (pos . source) pairs, indicating source information. POS
;; is relative to the beginning of the text section, and SOURCE is in
;; the same format that source-properties returns.
;;
(sources asm-sources set-asm-sources!)
;; A list of (pos . dead-slot-map) pairs, indicating dead slot maps.
;; POS is relative to the beginning of the text section.
;; DEAD-SLOT-MAP is a bitfield of slots that are dead at call sites,
;; as an integer.
;;
(dead-slot-maps asm-dead-slot-maps set-asm-dead-slot-maps!))
(define-inlinable (fresh-block)
(make-u32vector *block-size*))
(define* (make-assembler #:key (word-size (target-word-size))
(endianness (target-endianness)))
"Create an assembler for a given target @var{word-size} and
@var{endianness}, falling back to appropriate values for the configured
target."
(make-asm (fresh-block) 0 0 '() 0
(make-hash-table) '()
word-size endianness
vlist-null '()
(make-string-table) 1
'() '() '()))
(define (intern-section-name! asm string)
"Add a string to the section name table (shstrtab)."
(string-table-intern! (asm-shstrtab asm) string))
(define-inlinable (asm-pos asm)
"The offset of the next word to be written into the code buffer, in
32-bit units."
(+ (asm-idx asm) (asm-written asm)))
(define (allocate-new-block asm)
"Close off the current block, and arrange for the next word to be
written to a fresh block."
(let ((new (fresh-block)))
(set-asm-prev! asm (cons (asm-cur asm) (asm-prev asm)))
(set-asm-written! asm (asm-pos asm))
(set-asm-cur! asm new)
(set-asm-idx! asm 0)))
(define-inlinable (emit asm u32)
"Emit one 32-bit word into the instruction stream. Assumes that there
is space for the word, and ensures that there is space for the next
word."
(u32-set! (asm-cur asm) (asm-idx asm) u32)
(set-asm-idx! asm (1+ (asm-idx asm)))
(if (= (asm-idx asm) *block-size*)
(allocate-new-block asm)))
(define-inlinable (make-reloc type label base word)
"Make an internal relocation of type @var{type} referencing symbol
@var{label}, @var{word} words after position @var{start}. @var{type}
may be x8-s24, indicating a 24-bit relative label reference that can be
fixed up by the assembler, or s32, indicating a 32-bit relative
reference that needs to be fixed up by the linker."
(list type label base word))
(define-inlinable (reset-asm-start! asm)
"Reset the asm-start after writing the words for one instruction."
(set-asm-start! asm (asm-pos asm)))
(define (record-label-reference asm label)
"Record an x8-s24 local label reference. This value will get patched
up later by the assembler."
(let* ((start (asm-start asm))
(pos (asm-pos asm))
(reloc (make-reloc 'x8-s24 label start (- pos start))))
(set-asm-relocs! asm (cons reloc (asm-relocs asm)))))
(define* (record-far-label-reference asm label #:optional (offset 0))
"Record an s32 far label reference. This value will get patched up
later by the linker."
(let* ((start (- (asm-start asm) offset))
(pos (asm-pos asm))
(reloc (make-reloc 's32 label start (- pos start))))
(set-asm-relocs! asm (cons reloc (asm-relocs asm)))))
;;;
;;; Primitive assemblers are defined by expanding `assembler' for each
;;; opcode in `(instruction-list)'.
;;;
(eval-when (expand compile load eval)
(define (id-append ctx a b)
(datum->syntax ctx (symbol-append (syntax->datum a) (syntax->datum b)))))
(define-syntax assembler
(lambda (x)
(define-syntax op-case
(lambda (x)
(syntax-case x ()
((_ asm name ((type arg ...) code ...) clause ...)
#`(if (eq? name 'type)
(with-syntax (((arg ...) (generate-temporaries #'(arg ...))))
#'((arg ...)
code ...))
(op-case asm name clause ...)))
((_ asm name)
#'(error "unmatched name" name)))))
(define (pack-first-word asm opcode type)
(with-syntax ((opcode opcode))
(op-case
asm type
((U8_X24)
(emit asm opcode))
((U8_U24 arg)
(emit asm (pack-u8-u24 opcode arg)))
((U8_L24 label)
(record-label-reference asm label)
(emit asm opcode))
((U8_U8_I16 a imm)
(emit asm (pack-u8-u8-u16 opcode a (object-address imm))))
((U8_U12_U12 a b)
(emit asm (pack-u8-u12-u12 opcode a b)))
((U8_U8_U8_U8 a b c)
(emit asm (pack-u8-u8-u8-u8 opcode a b c))))))
(define (pack-tail-word asm type)
(op-case
asm type
((U8_U24 a b)
(emit asm (pack-u8-u24 a b)))
((U8_L24 a label)
(record-label-reference asm label)
(emit asm a))
((U8_U8_I16 a b imm)
(emit asm (pack-u8-u8-u16 a b (object-address imm))))
((U8_U12_U12 a b)
(emit asm (pack-u8-u12-u12 a b c)))
((U8_U8_U8_U8 a b c d)
(emit asm (pack-u8-u8-u8-u8 a b c d)))
((U32 a)
(emit asm a))
((I32 imm)
(let ((val (object-address imm)))
(unless (zero? (ash val -32))
(error "FIXME: enable truncation of negative fixnums when cross-compiling"))
(emit asm val)))
((A32 imm)
(unless (= (asm-word-size asm) 8)
(error "make-long-immediate unavailable for this target"))
(emit asm (ash (object-address imm) -32))
(emit asm (logand (object-address imm) (1- (ash 1 32)))))
((B32))
((N32 label)
(record-far-label-reference asm label)
(emit asm 0))
((S32 label)
(record-far-label-reference asm label)
(emit asm 0))
((L32 label)
(record-far-label-reference asm label)
(emit asm 0))
((LO32 label offset)
(record-far-label-reference asm label
(* offset (/ (asm-word-size asm) 4)))
(emit asm 0))
((X8_U24 a)
(emit asm (pack-u8-u24 0 a)))
((X8_U12_U12 a b)
(emit asm (pack-u8-u12-u12 0 a b)))
((X8_L24 label)
(record-label-reference asm label)
(emit asm 0))
((B1_X7_L24 a label)
(record-label-reference asm label)
(emit asm (pack-u1-u7-u24 (if a 1 0) 0 0)))
((B1_U7_L24 a b label)
(record-label-reference asm label)
(emit asm (pack-u1-u7-u24 (if a 1 0) b 0)))
((B1_X31 a)
(emit asm (pack-u1-u7-u24 (if a 1 0) 0 0)))
((B1_X7_U24 a b)
(emit asm (pack-u1-u7-u24 (if a 1 0) 0 b)))))
(syntax-case x ()
((_ name opcode word0 word* ...)
(with-syntax ((((formal0 ...)
code0 ...)
(pack-first-word #'asm
(syntax->datum #'opcode)
(syntax->datum #'word0)))
((((formal* ...)
code* ...) ...)
(map (lambda (word) (pack-tail-word #'asm word))
(syntax->datum #'(word* ...)))))
#'(lambda (asm formal0 ... formal* ... ...)
(unless (asm? asm) (error "not an asm"))
code0 ...
code* ... ...
(reset-asm-start! asm)))))))
(define assemblers (make-hash-table))
(define-syntax define-assembler
(lambda (x)
(syntax-case x ()
((_ name opcode kind arg ...)
(with-syntax ((emit (id-append #'name #'emit- #'name)))
#'(begin
(define emit
(let ((emit (assembler name opcode arg ...)))
(hashq-set! assemblers 'name emit)
emit))
(export emit)))))))
(define-syntax visit-opcodes
(lambda (x)
(syntax-case x ()
((visit-opcodes macro arg ...)
(with-syntax (((inst ...)
(map (lambda (x) (datum->syntax #'macro x))
(instruction-list))))
#'(begin
(macro arg ... . inst)
...))))))
(visit-opcodes define-assembler)
(define (emit-text asm instructions)
"Assemble @var{instructions} using the assembler @var{asm}.
@var{instructions} is a sequence of instructions, expressed as a list of
lists. This procedure can be called many times before calling
@code{link-assembly}."
(for-each (lambda (inst)
(apply (or (hashq-ref assemblers (car inst))
(error 'bad-instruction inst))
asm
(cdr inst)))
instructions))
;;;
;;; The constant table records a topologically sorted set of literal
;;; constants used by a program. For example, a pair uses its car and
;;; cdr, a string uses its stringbuf, etc.
;;;
;;; Some things we want to add to the constant table are not actually
;;; Scheme objects: for example, stringbufs, cache cells for toplevel
;;; references, or cache cells for non-closure procedures. For these we
;;; define special record types and add instances of those record types
;;; to the table.
;;;
(define-inlinable (immediate? x)
"Return @code{#t} if @var{x} is immediate, and @code{#f} otherwise."
(not (zero? (logand (object-address x) 6))))
(define-record-type <stringbuf>
(make-stringbuf string)
stringbuf?
(string stringbuf-string))
(define-record-type <static-procedure>
(make-static-procedure code)
static-procedure?
(code static-procedure-code))
(define-record-type <uniform-vector-backing-store>
(make-uniform-vector-backing-store bytes element-size)
uniform-vector-backing-store?
(bytes uniform-vector-backing-store-bytes)
(element-size uniform-vector-backing-store-element-size))
(define-record-type <cache-cell>
(make-cache-cell scope key)
cache-cell?
(scope cache-cell-scope)
(key cache-cell-key))
(define (simple-vector? obj)
(and (vector? obj)
(equal? (array-shape obj) (list (list 0 (1- (vector-length obj)))))))
(define (simple-uniform-vector? obj)
(and (array? obj)
(symbol? (array-type obj))
(equal? (array-shape obj) (list (list 0 (1- (array-length obj)))))))
(define (statically-allocatable? x)
"Return @code{#t} if a non-immediate constant can be allocated
statically, and @code{#f} if it would need some kind of runtime
allocation."
(or (pair? x) (string? x) (stringbuf? x) (static-procedure? x) (array? x)))
(define (intern-constant asm obj)
"Add an object to the constant table, and return a label that can be
used to reference it. If the object is already present in the constant
table, its existing label is used directly."
(define (recur obj)
(intern-constant asm obj))
(define (field dst n obj)
(let ((src (recur obj)))
(if src
(if (statically-allocatable? obj)
`((static-patch! ,dst ,n ,src))
`((static-ref 1 ,src)
(static-set! 1 ,dst ,n)))
'())))
(define (intern obj label)
(cond
((pair? obj)
(append (field label 0 (car obj))
(field label 1 (cdr obj))))
((simple-vector? obj)
(let lp ((i 0) (inits '()))
(if (< i (vector-length obj))
(lp (1+ i)
(append-reverse (field label (1+ i) (vector-ref obj i))
inits))
(reverse inits))))
((stringbuf? obj) '())
((static-procedure? obj)
`((static-patch! ,label 1 ,(static-procedure-code obj))))
((cache-cell? obj) '())
((symbol? obj)
`((make-non-immediate 1 ,(recur (symbol->string obj)))
(string->symbol 1 1)
(static-set! 1 ,label 0)))
((string? obj)
`((static-patch! ,label 1 ,(recur (make-stringbuf obj)))))
((keyword? obj)
`((static-ref 1 ,(recur (keyword->symbol obj)))
(symbol->keyword 1 1)
(static-set! 1 ,label 0)))
((number? obj)
`((make-non-immediate 1 ,(recur (number->string obj)))
(string->number 1 1)
(static-set! 1 ,label 0)))
((uniform-vector-backing-store? obj) '())
((simple-uniform-vector? obj)
(let ((width (case (array-type obj)
((vu8 u8 s8) 1)
((u16 s16) 2)
;; Bitvectors are addressed in 32-bit units.
;; Although a complex number is 8 or 16 bytes wide,
;; it should be byteswapped in 4 or 8 byte units.
((u32 s32 f32 c32 b) 4)
((u64 s64 f64 c64) 8)
(else
(error "unhandled array type" obj)))))
`((static-patch! ,label 2
,(recur (make-uniform-vector-backing-store
(uniform-array->bytevector obj)
width))))))
(else
(error "don't know how to intern" obj))))
(cond
((immediate? obj) #f)
((vhash-assoc obj (asm-constants asm)) => cdr)
(else
;; Note that calling intern may mutate asm-constants and
;; asm-constant-inits.
(let* ((label (gensym "constant"))
(inits (intern obj label)))
(set-asm-constants! asm (vhash-cons obj label (asm-constants asm)))
(set-asm-inits! asm (append-reverse inits (asm-inits asm)))
label))))
(define (intern-non-immediate asm obj)
"Intern a non-immediate into the constant table, and return its
label."
(when (immediate? obj)
(error "expected a non-immediate" obj))
(intern-constant asm obj))
(define (intern-cache-cell asm scope key)
"Intern a cache cell into the constant table, and return its label.
If there is already a cache cell with the given scope and key, it is
returned instead."
(intern-constant asm (make-cache-cell scope key)))
;; Return the label of the cell that holds the module for a scope.
(define (intern-module-cache-cell asm scope)
"Intern a cache cell for a module, and return its label."
(intern-cache-cell asm scope #t))
;;;
;;; Macro assemblers bridge the gap between primitive instructions and
;;; some higher-level operations.
;;;
(define-syntax define-macro-assembler
(lambda (x)
(syntax-case x ()
((_ (name arg ...) body body* ...)
(with-syntax ((emit (id-append #'name #'emit- #'name)))
#'(begin
(define emit
(let ((emit (lambda (arg ...) body body* ...)))
(hashq-set! assemblers 'name emit)
emit))
(export emit)))))))
(define-macro-assembler (load-constant asm dst obj)
(cond
((immediate? obj)
(let ((bits (object-address obj)))
(cond
((and (< dst 256) (zero? (ash bits -16)))
(emit-make-short-immediate asm dst obj))
((zero? (ash bits -32))
(emit-make-long-immediate asm dst obj))
(else
(emit-make-long-long-immediate asm dst obj)))))
((statically-allocatable? obj)
(emit-make-non-immediate asm dst (intern-non-immediate asm obj)))
(else
(emit-static-ref asm dst (intern-non-immediate asm obj)))))
(define-macro-assembler (load-static-procedure asm dst label)
(let ((loc (intern-constant asm (make-static-procedure label))))
(emit-make-non-immediate asm dst loc)))
(define-syntax-rule (define-tc7-macro-assembler name tc7)
(define-macro-assembler (name asm slot invert? label)
(emit-br-if-tc7 asm slot invert? tc7 label)))
;; Keep in sync with tags.h. Part of Guile's ABI. Currently unused
;; macro assemblers are commented out. See also
;; *branching-primcall-arities* in (language cps primitives), the set of
;; macro-instructions in assembly.scm, and
;; disassembler.scm:code-annotation.
;;
;; FIXME: Define all tc7 values in Scheme in one place, derived from
;; tags.h.
(define-tc7-macro-assembler br-if-symbol 5)
(define-tc7-macro-assembler br-if-variable 7)
(define-tc7-macro-assembler br-if-vector 13)
;(define-tc7-macro-assembler br-if-weak-vector 13)
(define-tc7-macro-assembler br-if-string 21)
;(define-tc7-macro-assembler br-if-heap-number 23)
;(define-tc7-macro-assembler br-if-stringbuf 39)
(define-tc7-macro-assembler br-if-bytevector 77)
;(define-tc7-macro-assembler br-if-pointer 31)
;(define-tc7-macro-assembler br-if-hashtable 29)
;(define-tc7-macro-assembler br-if-fluid 37)
;(define-tc7-macro-assembler br-if-dynamic-state 45)
;(define-tc7-macro-assembler br-if-frame 47)
;(define-tc7-macro-assembler br-if-vm 55)
;(define-tc7-macro-assembler br-if-vm-cont 71)
;(define-tc7-macro-assembler br-if-rtl-program 69)
;(define-tc7-macro-assembler br-if-weak-set 85)
;(define-tc7-macro-assembler br-if-weak-table 87)
;(define-tc7-macro-assembler br-if-array 93)
(define-tc7-macro-assembler br-if-bitvector 95)
;(define-tc7-macro-assembler br-if-port 125)
;(define-tc7-macro-assembler br-if-smob 127)
(define-macro-assembler (begin-program asm label properties)
(emit-label asm label)
(let ((meta (make-meta label properties (asm-start asm))))
(set-asm-meta! asm (cons meta (asm-meta asm)))))
(define-macro-assembler (end-program asm)
(let ((meta (car (asm-meta asm))))
(set-meta-high-pc! meta (asm-start asm))
(set-meta-arities! meta (reverse (meta-arities meta)))))
(define-macro-assembler (begin-standard-arity asm req nlocals alternate)
(emit-begin-opt-arity asm req '() #f nlocals alternate))
(define-macro-assembler (begin-opt-arity asm req opt rest nlocals alternate)
(emit-begin-kw-arity asm req opt rest '() #f nlocals alternate))
(define-macro-assembler (begin-kw-arity asm req opt rest kw-indices
allow-other-keys? nlocals alternate)
(assert-match req ((? symbol?) ...) "list of symbols")
(assert-match opt ((? symbol?) ...) "list of symbols")
(assert-match rest (or #f (? symbol?)) "#f or symbol")
(assert-match kw-indices (((? keyword?) . (? integer?)) ...)
"alist of keyword -> integer")
(assert-match allow-other-keys? (? boolean?) "boolean")
(assert-match nlocals (? integer?) "integer")
(assert-match alternate (or #f (? exact-integer?) (? symbol?)) "#f or symbol")
(let* ((meta (car (asm-meta asm)))
(arity (make-arity req opt rest kw-indices allow-other-keys?
(asm-start asm) #f '()))
;; The procedure itself is in slot 0, in the standard calling
;; convention. For procedure prologues, nreq includes the
;; procedure, so here we add 1.
(nreq (1+ (length req)))
(nopt (length opt))
(rest? (->bool rest)))
(set-meta-arities! meta (cons arity (meta-arities meta)))
(cond
((or allow-other-keys? (pair? kw-indices))
(emit-kw-prelude asm nreq nopt rest? kw-indices allow-other-keys?
nlocals alternate))
((or rest? (pair? opt))
(emit-opt-prelude asm nreq nopt rest? nlocals alternate))
(else
(emit-standard-prelude asm nreq nlocals alternate)))))
(define-macro-assembler (end-arity asm)
(let ((arity (car (meta-arities (car (asm-meta asm))))))
(set-arity-definitions! arity (reverse (arity-definitions arity)))
(set-arity-high-pc! arity (asm-start asm))))
(define-macro-assembler (standard-prelude asm nreq nlocals alternate)
(cond
(alternate
(emit-br-if-nargs-ne asm nreq alternate)
(emit-alloc-frame asm nlocals))
((and (< nreq (ash 1 12)) (< (- nlocals nreq) (ash 1 12)))
(emit-assert-nargs-ee/locals asm nreq (- nlocals nreq)))
(else
(emit-assert-nargs-ee asm nreq)
(emit-alloc-frame asm nlocals))))
(define-macro-assembler (opt-prelude asm nreq nopt rest? nlocals alternate)
(if alternate
(emit-br-if-nargs-lt asm nreq alternate)
(emit-assert-nargs-ge asm nreq))
(cond
(rest?
(emit-bind-rest asm (+ nreq nopt)))
(alternate
(emit-br-if-nargs-gt asm (+ nreq nopt) alternate))
(else
(emit-assert-nargs-le asm (+ nreq nopt))))
(emit-alloc-frame asm nlocals))
(define-macro-assembler (kw-prelude asm nreq nopt rest? kw-indices
allow-other-keys? nlocals alternate)
(if alternate
(begin
(emit-br-if-nargs-lt asm nreq alternate)
(unless rest?
(emit-br-if-npos-gt asm nreq (+ nreq nopt) alternate)))
(emit-assert-nargs-ge asm nreq))
(let ((ntotal (fold (lambda (kw ntotal)
(match kw
(((? keyword?) . idx)
(max (1+ idx) ntotal))))
(+ nreq nopt) kw-indices)))
;; FIXME: port 581f410f
(emit-bind-kwargs asm nreq
(pack-flags allow-other-keys? rest?)
(+ nreq nopt)
ntotal
(intern-constant asm kw-indices))
(emit-alloc-frame asm nlocals)))
(define-macro-assembler (label asm sym)
(hashq-set! (asm-labels asm) sym (asm-start asm)))
(define-macro-assembler (source asm source)
(set-asm-sources! asm (acons (asm-start asm) source (asm-sources asm))))
(define-macro-assembler (definition asm name slot)
(let* ((arity (car (meta-arities (car (asm-meta asm)))))
(def (vector name
slot
(* (- (asm-start asm) (arity-low-pc arity)) 4))))
(set-arity-definitions! arity (cons def (arity-definitions arity)))))
(define-macro-assembler (cache-current-module! asm module scope)
(let ((mod-label (intern-module-cache-cell asm scope)))
(emit-static-set! asm module mod-label 0)))
(define-macro-assembler (cached-toplevel-box asm dst scope sym bound?)
(let ((sym-label (intern-non-immediate asm sym))
(mod-label (intern-module-cache-cell asm scope))
(cell-label (intern-cache-cell asm scope sym)))
(emit-toplevel-box asm dst cell-label mod-label sym-label bound?)))
(define-macro-assembler (cached-module-box asm dst module-name sym public? bound?)
(let* ((sym-label (intern-non-immediate asm sym))
(key (cons public? module-name))
(mod-name-label (intern-constant asm key))
(cell-label (intern-cache-cell asm key sym)))
(emit-module-box asm dst cell-label mod-name-label sym-label bound?)))
(define-macro-assembler (dead-slot-map asm proc-slot dead-slot-map)
(unless (zero? dead-slot-map)
(set-asm-dead-slot-maps! asm
(cons
(cons* (asm-start asm) proc-slot dead-slot-map)
(asm-dead-slot-maps asm)))))
;;;
;;; Helper for linking objects.
;;;
(define (make-object asm name bv relocs labels . kwargs)
"Make a linker object. This helper handles interning the name in the
shstrtab, assigning the size, allocating a fresh index, and defining a
corresponding linker symbol for the start of the section."
(let ((name-idx (intern-section-name! asm (symbol->string name)))
(index (asm-next-section-number asm)))
(set-asm-next-section-number! asm (1+ index))
(make-linker-object (apply make-elf-section
#:index index
#:name name-idx
#:size (bytevector-length bv)
kwargs)
bv relocs
(cons (make-linker-symbol name 0) labels))))
;;;
;;; Linking the constant table. This code is somewhat intertwingled
;;; with the intern-constant code above, as that procedure also
;;; residualizes instructions to initialize constants at load time.
;;;
(define (write-immediate asm buf pos x)
(let ((val (object-address x))
(endianness (asm-endianness asm)))
(case (asm-word-size asm)
((4) (bytevector-u32-set! buf pos val endianness))
((8) (bytevector-u64-set! buf pos val endianness))
(else (error "bad word size" asm)))))
(define (emit-init-constants asm)
"If there is writable data that needs initialization at runtime, emit
a procedure to do that and return its label. Otherwise return
@code{#f}."
(let ((inits (asm-inits asm)))
(and (not (null? inits))
(let ((label (gensym "init-constants")))
(emit-text asm
`((begin-program ,label ())
(assert-nargs-ee/locals 1 1)
,@(reverse inits)
(load-constant 1 ,*unspecified*)
(return 1)
(end-program)))
label))))
(define (link-data asm data name)
"Link the static data for a program into the @var{name} section (which
should be .data or .rodata), and return the resulting linker object.
@var{data} should be a vhash mapping objects to labels."
(define (align address alignment)
(+ address
(modulo (- alignment (modulo address alignment)) alignment)))
(define tc7-vector 13)
(define stringbuf-shared-flag #x100)
(define stringbuf-wide-flag #x400)
(define tc7-stringbuf 39)
(define tc7-narrow-stringbuf
(+ tc7-stringbuf stringbuf-shared-flag))
(define tc7-wide-stringbuf
(+ tc7-stringbuf stringbuf-shared-flag stringbuf-wide-flag))
(define tc7-ro-string (+ 21 #x200))
(define tc7-program 69)
(define tc7-bytevector 77)
(define tc7-bitvector 95)
(let ((word-size (asm-word-size asm))
(endianness (asm-endianness asm)))
(define (byte-length x)
(cond
((stringbuf? x)
(let ((x (stringbuf-string x)))
(+ (* 2 word-size)
(case (string-bytes-per-char x)
((1) (1+ (string-length x)))
((4) (* (1+ (string-length x)) 4))
(else (error "bad string bytes per char" x))))))
((static-procedure? x)
(* 2 word-size))
((string? x)
(* 4 word-size))
((pair? x)
(* 2 word-size))
((simple-vector? x)
(* (1+ (vector-length x)) word-size))
((simple-uniform-vector? x)
(* 4 word-size))
((uniform-vector-backing-store? x)
(bytevector-length (uniform-vector-backing-store-bytes x)))
(else
word-size)))
(define (write-constant-reference buf pos x)
;; The asm-inits will fix up any reference to a non-immediate.
(write-immediate asm buf pos (if (immediate? x) x #f)))
(define (write buf pos obj)
(cond
((stringbuf? obj)
(let* ((x (stringbuf-string obj))
(len (string-length x))
(tag (if (= (string-bytes-per-char x) 1)
tc7-narrow-stringbuf
tc7-wide-stringbuf)))
(case word-size
((4)
(bytevector-u32-set! buf pos tag endianness)
(bytevector-u32-set! buf (+ pos 4) len endianness))
((8)
(bytevector-u64-set! buf pos tag endianness)
(bytevector-u64-set! buf (+ pos 8) len endianness))
(else
(error "bad word size" asm)))
(let ((pos (+ pos (* word-size 2))))
(case (string-bytes-per-char x)
((1)
(let lp ((i 0))
(if (< i len)
(let ((u8 (char->integer (string-ref x i))))
(bytevector-u8-set! buf (+ pos i) u8)
(lp (1+ i)))
(bytevector-u8-set! buf (+ pos i) 0))))
((4)
(let lp ((i 0))
(if (< i len)
(let ((u32 (char->integer (string-ref x i))))
(bytevector-u32-set! buf (+ pos (* i 4)) u32 endianness)
(lp (1+ i)))
(bytevector-u32-set! buf (+ pos (* i 4)) 0 endianness))))
(else (error "bad string bytes per char" x))))))
((static-procedure? obj)
(case word-size
((4)
(bytevector-u32-set! buf pos tc7-program endianness)
(bytevector-u32-set! buf (+ pos 4) 0 endianness))
((8)
(bytevector-u64-set! buf pos tc7-program endianness)
(bytevector-u64-set! buf (+ pos 8) 0 endianness))
(else (error "bad word size"))))
((cache-cell? obj)
(write-immediate asm buf pos #f))
((string? obj)
(let ((tag (logior tc7-ro-string (ash (string-length obj) 8))))
(case word-size
((4)
(bytevector-u32-set! buf pos tc7-ro-string endianness)
(write-immediate asm buf (+ pos 4) #f) ; stringbuf
(bytevector-u32-set! buf (+ pos 8) 0 endianness)
(bytevector-u32-set! buf (+ pos 12) (string-length obj) endianness))
((8)
(bytevector-u64-set! buf pos tc7-ro-string endianness)
(write-immediate asm buf (+ pos 8) #f) ; stringbuf
(bytevector-u64-set! buf (+ pos 16) 0 endianness)
(bytevector-u64-set! buf (+ pos 24) (string-length obj) endianness))
(else (error "bad word size")))))
((pair? obj)
(write-constant-reference buf pos (car obj))
(write-constant-reference buf (+ pos word-size) (cdr obj)))
((simple-vector? obj)
(let* ((len (vector-length obj))
(tag (logior tc7-vector (ash len 8))))
(case word-size
((4) (bytevector-u32-set! buf pos tag endianness))
((8) (bytevector-u64-set! buf pos tag endianness))
(else (error "bad word size")))
(let lp ((i 0))
(when (< i (vector-length obj))
(let ((pos (+ pos word-size (* i word-size)))
(elt (vector-ref obj i)))
(write-constant-reference buf pos elt)
(lp (1+ i)))))))
((symbol? obj)
(write-immediate asm buf pos #f))
((keyword? obj)
(write-immediate asm buf pos #f))
((number? obj)
(write-immediate asm buf pos #f))
((simple-uniform-vector? obj)
(let ((tag (if (bitvector? obj)
tc7-bitvector
(let ((type-code (array-type-code obj)))
(logior tc7-bytevector (ash type-code 7))))))
(case word-size
((4)
(bytevector-u32-set! buf pos tag endianness)
(bytevector-u32-set! buf (+ pos 4)
(if (bitvector? obj)
(bitvector-length obj)
(bytevector-length obj))
endianness) ; length
(bytevector-u32-set! buf (+ pos 8) 0 endianness) ; pointer
(write-immediate asm buf (+ pos 12) #f)) ; owner
((8)
(bytevector-u64-set! buf pos tag endianness)
(bytevector-u64-set! buf (+ pos 8)
(if (bitvector? obj)
(bitvector-length obj)
(bytevector-length obj))
endianness) ; length
(bytevector-u64-set! buf (+ pos 16) 0 endianness) ; pointer
(write-immediate asm buf (+ pos 24) #f)) ; owner
(else (error "bad word size")))))
((uniform-vector-backing-store? obj)
(let ((bv (uniform-vector-backing-store-bytes obj)))
(bytevector-copy! bv 0 buf pos (bytevector-length bv))
(unless (or (= 1 (uniform-vector-backing-store-element-size obj))
(eq? endianness (native-endianness)))
;; Need to swap units of element-size bytes
(error "FIXME: Implement byte order swap"))))
(else
(error "unrecognized object" obj))))
(cond
((vlist-null? data) #f)
(else
(let* ((byte-len (vhash-fold (lambda (k v len)
(+ (byte-length k) (align len 8)))
0 data))
(buf (make-bytevector byte-len 0)))
(let lp ((i 0) (pos 0) (symbols '()))
(if (< i (vlist-length data))
(let* ((pair (vlist-ref data i))
(obj (car pair))
(obj-label (cdr pair)))
(write buf pos obj)
(lp (1+ i)
(align (+ (byte-length obj) pos) 8)
(cons (make-linker-symbol obj-label pos) symbols)))
(make-object asm name buf '() symbols
#:flags (match name
('.data (logior SHF_ALLOC SHF_WRITE))
('.rodata SHF_ALLOC))))))))))
(define (link-constants asm)
"Link sections to hold constants needed by the program text emitted
using @var{asm}.
Returns three values: an object for the .rodata section, an object for
the .data section, and a label for an initialization procedure. Any of
these may be @code{#f}."
(define (shareable? x)
(cond
((stringbuf? x) #t)
((pair? x)
(and (immediate? (car x)) (immediate? (cdr x))))
((simple-vector? x)
(let lp ((i 0))
(or (= i (vector-length x))
(and (immediate? (vector-ref x i))
(lp (1+ i))))))
((uniform-vector-backing-store? x) #t)
(else #f)))
(let* ((constants (asm-constants asm))
(len (vlist-length constants)))
(let lp ((i 0)
(ro vlist-null)
(rw vlist-null))
(if (= i len)
(values (link-data asm ro '.rodata)
(link-data asm rw '.data)
(emit-init-constants asm))
(let ((pair (vlist-ref constants i)))
(if (shareable? (car pair))
(lp (1+ i) (vhash-consq (car pair) (cdr pair) ro) rw)
(lp (1+ i) ro (vhash-consq (car pair) (cdr pair) rw))))))))
;;;
;;; Linking program text.
;;;
(define (process-relocs buf relocs labels)
"Patch up internal x8-s24 relocations, and any s32 relocations that
reference symbols in the text section. Return a list of linker
relocations for references to symbols defined outside the text section."
(fold
(lambda (reloc tail)
(match reloc
((type label base word)
(let ((abs (hashq-ref labels label))
(dst (+ base word)))
(case type
((s32)
(if abs
(let ((rel (- abs base)))
(s32-set! buf dst rel)
tail)
(cons (make-linker-reloc 'rel32/4 (* dst 4) word label)
tail)))
((x8-s24)
(unless abs
(error "unbound near relocation" reloc))
(let ((rel (- abs base))
(u32 (u32-ref buf dst)))
(u32-set! buf dst (pack-u8-s24 (logand u32 #xff) rel))
tail))
(else (error "bad relocation kind" reloc)))))))
'()
relocs))
(define (process-labels labels)
"Define linker symbols for the label-offset map in @var{labels}.
The offsets are expected to be expressed in words."
(hash-map->list (lambda (label loc)
(make-linker-symbol label (* loc 4)))
labels))
(define (swap-bytes! buf)
"Patch up the text buffer @var{buf}, swapping the endianness of each
32-bit unit."
(unless (zero? (modulo (bytevector-length buf) 4))
(error "unexpected length"))
(let ((byte-len (bytevector-length buf)))
(let lp ((pos 0))
(unless (= pos byte-len)
(bytevector-u32-set!
buf pos
(bytevector-u32-ref buf pos (endianness big))
(endianness little))
(lp (+ pos 4))))))
(define (link-text-object asm)
"Link the .rtl-text section, swapping the endianness of the bytes if
needed."
(let ((buf (make-u32vector (asm-pos asm))))
(let lp ((pos 0) (prev (reverse (asm-prev asm))))
(if (null? prev)
(let ((byte-size (* (asm-idx asm) 4)))
(bytevector-copy! (asm-cur asm) 0 buf pos byte-size)
(unless (eq? (asm-endianness asm) (native-endianness))
(swap-bytes! buf))
(make-object asm '.rtl-text
buf
(process-relocs buf (asm-relocs asm)
(asm-labels asm))
(process-labels (asm-labels asm))))
(let ((len (* *block-size* 4)))
(bytevector-copy! (car prev) 0 buf pos len)
(lp (+ pos len) (cdr prev)))))))
;;;
;;; Create the frame maps. These maps are used by GC to identify dead
;;; slots in pending call frames, to avoid marking them. We only do
;;; this when frame makes a non-tail call, as that is the common case.
;;; Only the topmost frame will see a GC at any other point, but we mark
;;; top frames conservatively as serializing live slot maps at every
;;; instruction would take up too much space in the object file.
;;;
;; The .guile.frame-maps section starts with two packed u32 values: one
;; indicating the offset of the first byte of the .rtl-text section, and
;; another indicating the relative offset in bytes of the slots data.
(define frame-maps-prefix-len 8)
;; Each header is 8 bytes: 4 for the offset from .rtl_text, and 4 for
;; the offset of the slot map from the beginning of the
;; .guile.frame-maps section. The length of a frame map depends on the
;; frame size at the call site, and is not encoded into this section as
;; it is available at run-time.
(define frame-map-header-len 8)
(define (link-frame-maps asm)
(define (map-byte-length proc-slot)
(ceiling-quotient (- proc-slot 2) 8))
(define (make-frame-maps maps count map-len)
(let* ((endianness (asm-endianness asm))
(header-pos frame-maps-prefix-len)
(map-pos (+ header-pos (* count frame-map-header-len)))
(bv (make-bytevector (+ map-pos map-len) 0)))
(bytevector-u32-set! bv 4 map-pos endianness)
(let lp ((maps maps) (header-pos header-pos) (map-pos map-pos))
(match maps
(()
(make-object asm '.guile.frame-maps bv
(list (make-linker-reloc 'abs32/1 0 0 '.rtl-text))
'() #:type SHT_PROGBITS #:flags SHF_ALLOC))
(((pos proc-slot . map) . maps)
(bytevector-u32-set! bv header-pos (* pos 4) endianness)
(bytevector-u32-set! bv (+ header-pos 4) map-pos endianness)
(let write-bytes ((map-pos map-pos)
(map map)
(byte-length (map-byte-length proc-slot)))
(if (zero? byte-length)
(lp maps (+ header-pos frame-map-header-len) map-pos)
(begin
(bytevector-u8-set! bv map-pos (logand map #xff))
(write-bytes (1+ map-pos) (ash map -8)
(1- byte-length))))))))))
(match (asm-dead-slot-maps asm)
(() #f)
(in
(let lp ((in in) (out '()) (count 0) (map-len 0))
(match in
(() (make-frame-maps out count map-len))
(((and head (pos proc-slot . map)) . in)
(lp in (cons head out)
(1+ count)
(+ (map-byte-length proc-slot) map-len))))))))
;;;
;;; Linking other sections of the ELF file, like the dynamic segment,
;;; the symbol table, etc.
;;;
;; FIXME: Define these somewhere central, shared with C.
(define *bytecode-major-version* #x0202)
(define *bytecode-minor-version* 5)
(define (link-dynamic-section asm text rw rw-init frame-maps)
"Link the dynamic section for an ELF image with bytecode @var{text},
given the writable data section @var{rw} needing fixup from the
procedure with label @var{rw-init}. @var{rw-init} may be false. If
@var{rw} is true, it will be added to the GC roots at runtime."
(define-syntax-rule (emit-dynamic-section word-size %set-uword! reloc-type)
(let* ((endianness (asm-endianness asm))
(words 6)
(words (if rw (+ words 4) words))
(words (if rw-init (+ words 2) words))
(words (if frame-maps (+ words 2) words))
(bv (make-bytevector (* word-size words) 0))
(set-uword!
(lambda (i uword)
(%set-uword! bv (* i word-size) uword endianness)))
(relocs '())
(set-label!
(lambda (i label)
(set! relocs (cons (make-linker-reloc 'reloc-type
(* i word-size) 0 label)
relocs))
(%set-uword! bv (* i word-size) 0 endianness))))
(set-uword! 0 DT_GUILE_VM_VERSION)
(set-uword! 1 (logior (ash *bytecode-major-version* 16)
*bytecode-minor-version*))
(set-uword! 2 DT_GUILE_ENTRY)
(set-label! 3 '.rtl-text)
(when rw
;; Add roots to GC.
(set-uword! 4 DT_GUILE_GC_ROOT)
(set-label! 5 '.data)
(set-uword! 6 DT_GUILE_GC_ROOT_SZ)
(set-uword! 7 (bytevector-length (linker-object-bv rw)))
(when rw-init
(set-uword! 8 DT_INIT) ; constants
(set-label! 9 rw-init)))
(when frame-maps
(set-uword! (- words 4) DT_GUILE_FRAME_MAPS)
(set-label! (- words 3) '.guile.frame-maps))
(set-uword! (- words 2) DT_NULL)
(set-uword! (- words 1) 0)
(make-object asm '.dynamic bv relocs '()
#:type SHT_DYNAMIC #:flags SHF_ALLOC)))
(case (asm-word-size asm)
((4) (emit-dynamic-section 4 bytevector-u32-set! abs32/1))
((8) (emit-dynamic-section 8 bytevector-u64-set! abs64/1))
(else (error "bad word size" asm))))
(define (link-shstrtab asm)
"Link the string table for the section headers."
(intern-section-name! asm ".shstrtab")
(make-object asm '.shstrtab
(link-string-table! (asm-shstrtab asm))
'() '()
#:type SHT_STRTAB #:flags 0))
(define (link-symtab text-section asm)
(let* ((endianness (asm-endianness asm))
(word-size (asm-word-size asm))
(size (elf-symbol-len word-size))
(meta (reverse (asm-meta asm)))
(n (length meta))
(strtab (make-string-table))
(bv (make-bytevector (* n size) 0)))
(define (intern-string! name)
(string-table-intern! strtab (if name (symbol->string name) "")))
(for-each
(lambda (meta n)
(let ((name (intern-string! (meta-name meta))))
(write-elf-symbol bv (* n size) endianness word-size
(make-elf-symbol
#:name name
;; Symbol value and size are measured in
;; bytes, not u32s.
#:value (* 4 (meta-low-pc meta))
#:size (* 4 (- (meta-high-pc meta)
(meta-low-pc meta)))
#:type STT_FUNC
#:visibility STV_HIDDEN
#:shndx (elf-section-index text-section)))))
meta (iota n))
(let ((strtab (make-object asm '.strtab
(link-string-table! strtab)
'() '()
#:type SHT_STRTAB #:flags 0)))
(values (make-object asm '.symtab
bv
'() '()
#:type SHT_SYMTAB #:flags 0 #:entsize size
#:link (elf-section-index
(linker-object-section strtab)))
strtab))))
;;; The .guile.arities section describes the arities that a function can
;;; have. It is in two parts: a sorted array of headers describing
;;; basic arities, and an array of links out to a string table (and in
;;; the case of keyword arguments, to the data section) for argument
;;; names. The whole thing is prefixed by a uint32 indicating the
;;; offset of the end of the headers array.
;;;
;;; The arity headers array is a packed array of structures of the form:
;;;
;;; struct arity_header {
;;; uint32_t low_pc;
;;; uint32_t high_pc;
;;; uint32_t offset;
;;; uint32_t flags;
;;; uint32_t nreq;
;;; uint32_t nopt;
;;; uint32_t nlocals;
;;; }
;;;
;;; All of the offsets and addresses are 32 bits. We can expand in the
;;; future to use 64-bit offsets if appropriate, but there are other
;;; aspects of bytecode that constrain us to a total image that fits in
;;; 32 bits, so for the moment we'll simplify the problem space.
;;;
;;; The following flags values are defined:
;;;
;;; #x1: has-rest?
;;; #x2: allow-other-keys?
;;; #x4: has-keyword-args?
;;; #x8: is-case-lambda?
;;; #x10: is-in-case-lambda?
;;;
;;; Functions with a single arity specify their number of required and
;;; optional arguments in nreq and nopt, and do not have the
;;; is-case-lambda? flag set. Their "offset" member links to an array
;;; of pointers into the associated .guile.arities.strtab string table,
;;; identifying the argument names. This offset is relative to the
;;; start of the .guile.arities section.
;;;
;;; If the arity has keyword arguments -- if has-keyword-args? is set in
;;; the flags -- the first uint32 pointed to by offset encodes a link to
;;; the "keyword indices" literal, in the data section. Then follow the
;;; names for all locals, in order, as uleb128 values. The required
;;; arguments will be the first locals, followed by the optionals,
;;; followed by the rest argument if if has-rest? is set. The names
;;; point into the associated string table section.
;;;
;;; Functions with no arities have no arities information present in the
;;; .guile.arities section.
;;;
;;; Functions with multiple arities are preceded by a header with
;;; is-case-lambda? set. All other fields are 0, except low-pc and
;;; high-pc which should be the bounds of the whole function. Headers
;;; for the individual arities follow, with the is-in-case-lambda? flag
;;; set. In this way the whole headers array is sorted in increasing
;;; low-pc order, and case-lambda clauses are contained within the
;;; [low-pc, high-pc] of the case-lambda header.
;; Length of the prefix to the arities section, in bytes.
(define arities-prefix-len 4)
;; Length of an arity header, in bytes.
(define arity-header-len (* 7 4))
;; Some helpers.
(define (put-uleb128 port val)
(let lp ((val val))
(let ((next (ash val -7)))
(if (zero? next)
(put-u8 port val)
(begin
(put-u8 port (logior #x80 (logand val #x7f)))
(lp next))))))
(define (put-sleb128 port val)
(let lp ((val val))
(if (<= 0 (+ val 64) 127)
(put-u8 port (logand val #x7f))
(begin
(put-u8 port (logior #x80 (logand val #x7f)))
(lp (ash val -7))))))
(define (port-position port)
(seek port 0 SEEK_CUR))
(define-syntax-rule (pack-arity-flags has-rest? allow-other-keys?
has-keyword-args? is-case-lambda?
is-in-case-lambda?)
(logior (if has-rest? (ash 1 0) 0)
(if allow-other-keys? (ash 1 1) 0)
(if has-keyword-args? (ash 1 2) 0)
(if is-case-lambda? (ash 1 3) 0)
(if is-in-case-lambda? (ash 1 4) 0)))
(define (write-arities asm metas headers names-port strtab)
(define (write-header pos low-pc high-pc offset flags nreq nopt nlocals)
(unless (<= (+ nreq nopt) nlocals)
(error "forgot to emit definition instructions?"))
(bytevector-u32-set! headers pos (* low-pc 4) (asm-endianness asm))
(bytevector-u32-set! headers (+ pos 4) (* high-pc 4) (asm-endianness asm))
(bytevector-u32-set! headers (+ pos 8) offset (asm-endianness asm))
(bytevector-u32-set! headers (+ pos 12) flags (asm-endianness asm))
(bytevector-u32-set! headers (+ pos 16) nreq (asm-endianness asm))
(bytevector-u32-set! headers (+ pos 20) nopt (asm-endianness asm))
(bytevector-u32-set! headers (+ pos 24) nlocals (asm-endianness asm)))
(define (write-kw-indices kw-indices relocs)
;; FIXME: Assert that kw-indices is already interned.
(if (pair? kw-indices)
(let ((pos (+ (bytevector-length headers)
(port-position names-port)))
(label (intern-constant asm kw-indices)))
(put-bytevector names-port #vu8(0 0 0 0))
(cons (make-linker-reloc 'abs32/1 pos 0 label) relocs))
relocs))
(define (write-arity pos arity in-case-lambda? relocs)
(write-header pos (arity-low-pc arity)
(arity-high-pc arity)
;; FIXME: Seems silly to add on bytevector-length of
;; headers, given the arities-prefix.
(+ (bytevector-length headers) (port-position names-port))
(pack-arity-flags (arity-rest arity)
(arity-allow-other-keys? arity)
(pair? (arity-kw-indices arity))
#f
in-case-lambda?)
(length (arity-req arity))
(length (arity-opt arity))
(length (arity-definitions arity)))
(let ((relocs (write-kw-indices (arity-kw-indices arity) relocs)))
;; Write local names.
(let lp ((definitions (arity-definitions arity)))
(match definitions
(() relocs)
((#(name slot def) . definitions)
(let ((sym (if (symbol? name)
(string-table-intern! strtab (symbol->string name))
0)))
(put-uleb128 names-port sym)
(lp definitions)))))
;; Now write their definitions.
(let lp ((definitions (arity-definitions arity)))
(match definitions
(() relocs)
((#(name slot def) . definitions)
(put-uleb128 names-port def)
(put-uleb128 names-port slot)
(lp definitions))))))
(let lp ((metas metas) (pos arities-prefix-len) (relocs '()))
(match metas
(()
(unless (= pos (bytevector-length headers))
(error "expected to fully fill the bytevector"
pos (bytevector-length headers)))
relocs)
((meta . metas)
(match (meta-arities meta)
(() (lp metas pos relocs))
((arity)
(lp metas
(+ pos arity-header-len)
(write-arity pos arity #f relocs)))
(arities
;; Write a case-lambda header, then individual arities.
;; The case-lambda header's offset link is 0.
(write-header pos (meta-low-pc meta) (meta-high-pc meta) 0
(pack-arity-flags #f #f #f #t #f) 0 0 0)
(let lp* ((arities arities) (pos (+ pos arity-header-len))
(relocs relocs))
(match arities
(() (lp metas pos relocs))
((arity . arities)
(lp* arities
(+ pos arity-header-len)
(write-arity pos arity #t relocs)))))))))))
(define (link-arities asm)
(define (meta-arities-header-size meta)
(define (lambda-size arity)
arity-header-len)
(define (case-lambda-size arities)
(fold +
arity-header-len ;; case-lambda header
(map lambda-size arities))) ;; the cases
(match (meta-arities meta)
(() 0)
((arity) (lambda-size arity))
(arities (case-lambda-size arities))))
(define (bytevector-append a b)
(let ((out (make-bytevector (+ (bytevector-length a)
(bytevector-length b)))))
(bytevector-copy! a 0 out 0 (bytevector-length a))
(bytevector-copy! b 0 out (bytevector-length a) (bytevector-length b))
out))
(let* ((endianness (asm-endianness asm))
(metas (reverse (asm-meta asm)))
(header-size (fold (lambda (meta size)
(+ size (meta-arities-header-size meta)))
arities-prefix-len
metas))
(strtab (make-string-table))
(headers (make-bytevector header-size 0)))
(bytevector-u32-set! headers 0 (bytevector-length headers) endianness)
(let-values (((names-port get-name-bv) (open-bytevector-output-port)))
(let* ((relocs (write-arities asm metas headers names-port strtab))
(strtab (make-object asm '.guile.arities.strtab
(link-string-table! strtab)
'() '()
#:type SHT_STRTAB #:flags 0)))
(values (make-object asm '.guile.arities
(bytevector-append headers (get-name-bv))
relocs '()
#:type SHT_PROGBITS #:flags 0
#:link (elf-section-index
(linker-object-section strtab)))
strtab)))))
;;;
;;; The .guile.docstrs section is a packed, sorted array of (pc, str)
;;; values. Pc and str are both 32 bits wide. (Either could change to
;;; 64 bits if appropriate in the future.) Pc is the address of the
;;; entry to a program, relative to the start of the text section, in
;;; bytes, and str is an index into the associated .guile.docstrs.strtab
;;; string table section.
;;;
;; The size of a docstrs entry, in bytes.
(define docstr-size 8)
(define (link-docstrs asm)
(define (find-docstrings)
(filter-map (lambda (meta)
(define (is-documentation? pair)
(eq? (car pair) 'documentation))
(let* ((props (meta-properties meta))
(tail (find-tail is-documentation? props)))
(and tail
(not (find-tail is-documentation? (cdr tail)))
(string? (cdar tail))
(cons (* 4 (meta-low-pc meta)) (cdar tail)))))
(reverse (asm-meta asm))))
(let* ((endianness (asm-endianness asm))
(docstrings (find-docstrings))
(strtab (make-string-table))
(bv (make-bytevector (* (length docstrings) docstr-size) 0)))
(fold (lambda (pair pos)
(match pair
((pc . string)
(bytevector-u32-set! bv pos pc endianness)
(bytevector-u32-set! bv (+ pos 4)
(string-table-intern! strtab string)
endianness)
(+ pos docstr-size))))
0
docstrings)
(let ((strtab (make-object asm '.guile.docstrs.strtab
(link-string-table! strtab)
'() '()
#:type SHT_STRTAB #:flags 0)))
(values (make-object asm '.guile.docstrs
bv
'() '()
#:type SHT_PROGBITS #:flags 0
#:link (elf-section-index
(linker-object-section strtab)))
strtab))))
;;;
;;; The .guile.procprops section is a packed, sorted array of (pc, addr)
;;; values. Pc and addr are both 32 bits wide. (Either could change to
;;; 64 bits if appropriate in the future.) Pc is the address of the
;;; entry to a program, relative to the start of the text section, and
;;; addr is the address of the associated properties alist, relative to
;;; the start of the ELF image.
;;;
;;; Since procedure properties are stored in the data sections, we need
;;; to link the procedures property section first. (Note that this
;;; constraint does not apply to the arities section, which may
;;; reference the data sections via the kw-indices literal, because
;;; assembling the text section already makes sure that the kw-indices
;;; are interned.)
;;;
;; The size of a procprops entry, in bytes.
(define procprops-size 8)
(define (link-procprops asm)
(define (assoc-remove-one alist key value-pred)
(match alist
(() '())
((((? (lambda (x) (eq? x key))) . value) . alist)
(if (value-pred value)
alist
(acons key value alist)))
(((k . v) . alist)
(acons k v (assoc-remove-one alist key value-pred)))))
(define (props-without-name-or-docstring meta)
(assoc-remove-one
(assoc-remove-one (meta-properties meta) 'name (lambda (x) #t))
'documentation
string?))
(define (find-procprops)
(filter-map (lambda (meta)
(let ((props (props-without-name-or-docstring meta)))
(and (pair? props)
(cons (* 4 (meta-low-pc meta)) props))))
(reverse (asm-meta asm))))
(let* ((endianness (asm-endianness asm))
(procprops (find-procprops))
(bv (make-bytevector (* (length procprops) procprops-size) 0)))
(let lp ((procprops procprops) (pos 0) (relocs '()))
(match procprops
(()
(make-object asm '.guile.procprops
bv
relocs '()
#:type SHT_PROGBITS #:flags 0))
(((pc . props) . procprops)
(bytevector-u32-set! bv pos pc endianness)
(lp procprops
(+ pos procprops-size)
(cons (make-linker-reloc 'abs32/1 (+ pos 4) 0
(intern-constant asm props))
relocs)))))))
;;;
;;; The DWARF .debug_info, .debug_abbrev, .debug_str, and .debug_loc
;;; sections provide line number and local variable liveness
;;; information. Their format is defined by the DWARF
;;; specifications.
;;;
(define (asm-language asm)
;; FIXME: Plumb language through to the assembler.
'scheme)
;; -> 5 values: .debug_info, .debug_abbrev, .debug_str, .debug_loc, .debug_lines
(define (link-debug asm)
(define (put-s8 port val)
(let ((bv (make-bytevector 1)))
(bytevector-s8-set! bv 0 val)
(put-bytevector port bv)))
(define (put-u16 port val)
(let ((bv (make-bytevector 2)))
(bytevector-u16-set! bv 0 val (asm-endianness asm))
(put-bytevector port bv)))
(define (put-u32 port val)
(let ((bv (make-bytevector 4)))
(bytevector-u32-set! bv 0 val (asm-endianness asm))
(put-bytevector port bv)))
(define (put-u64 port val)
(let ((bv (make-bytevector 8)))
(bytevector-u64-set! bv 0 val (asm-endianness asm))
(put-bytevector port bv)))
(define (meta->subprogram-die meta)
`(subprogram
(@ ,@(cond
((meta-name meta)
=> (lambda (name) `((name ,(symbol->string name)))))
(else
'()))
(low-pc ,(meta-label meta))
(high-pc ,(* 4 (- (meta-high-pc meta) (meta-low-pc meta)))))))
(define (make-compile-unit-die asm)
`(compile-unit
(@ (producer ,(string-append "Guile " (version)))
(language ,(asm-language asm))
(low-pc .rtl-text)
(high-pc ,(* 4 (asm-pos asm)))
(stmt-list 0))
,@(map meta->subprogram-die (reverse (asm-meta asm)))))
(let-values (((die-port get-die-bv) (open-bytevector-output-port))
((die-relocs) '())
((abbrev-port get-abbrev-bv) (open-bytevector-output-port))
;; (tag has-kids? attrs forms) -> code
((abbrevs) vlist-null)
((strtab) (make-string-table))
((line-port get-line-bv) (open-bytevector-output-port))
((line-relocs) '())
;; file -> code
((files) vlist-null))
(define (write-abbrev code tag has-children? attrs forms)
(put-uleb128 abbrev-port code)
(put-uleb128 abbrev-port (tag-name->code tag))
(put-u8 abbrev-port (children-name->code (if has-children? 'yes 'no)))
(for-each (lambda (attr form)
(put-uleb128 abbrev-port (attribute-name->code attr))
(put-uleb128 abbrev-port (form-name->code form)))
attrs forms)
(put-uleb128 abbrev-port 0)
(put-uleb128 abbrev-port 0))
(define (intern-abbrev tag has-children? attrs forms)
(let ((key (list tag has-children? attrs forms)))
(match (vhash-assoc key abbrevs)
((_ . code) code)
(#f (let ((code (1+ (vlist-length abbrevs))))
(set! abbrevs (vhash-cons key code abbrevs))
(write-abbrev code tag has-children? attrs forms)
code)))))
(define (intern-file file)
(match (vhash-assoc file files)
((_ . code) code)
(#f (let ((code (1+ (vlist-length files))))
(set! files (vhash-cons file code files))
code))))
(define (write-sources)
;; Choose line base and line range values that will allow for an
;; address advance range of 16 words. The special opcode range is
;; from 10 to 255, so 246 values.
(define base -4)
(define range 15)
(let lp ((sources (asm-sources asm)) (out '()))
(match sources
(((pc . s) . sources)
(let ((file (assq-ref s 'filename))
(line (assq-ref s 'line))
(col (assq-ref s 'column)))
(lp sources
;; Guile line and column numbers are 0-indexed, but
;; they are 1-indexed for DWARF.
(cons (list pc
(if file (intern-file file) 0)
(if line (1+ line))
(if col (1+ col)))
out))))
(()
;; Compilation unit header for .debug_line. We write in
;; DWARF 2 format because more tools understand it than DWARF
;; 4, which incompatibly adds another field to this header.
(put-u32 line-port 0) ; Length; will patch later.
(put-u16 line-port 2) ; DWARF 2 format.
(put-u32 line-port 0) ; Prologue length; will patch later.
(put-u8 line-port 4) ; Minimum instruction length: 4 bytes.
(put-u8 line-port 1) ; Default is-stmt: true.
(put-s8 line-port base) ; Line base. See the DWARF standard.
(put-u8 line-port range) ; Line range. See the DWARF standard.
(put-u8 line-port 10) ; Opcode base: the first "special" opcode.
;; A table of the number of uleb128 arguments taken by each
;; of the standard opcodes.
(put-u8 line-port 0) ; 1: copy
(put-u8 line-port 1) ; 2: advance-pc
(put-u8 line-port 1) ; 3: advance-line
(put-u8 line-port 1) ; 4: set-file
(put-u8 line-port 1) ; 5: set-column
(put-u8 line-port 0) ; 6: negate-stmt
(put-u8 line-port 0) ; 7: set-basic-block
(put-u8 line-port 0) ; 8: const-add-pc
(put-u8 line-port 1) ; 9: fixed-advance-pc
;; Include directories, as a zero-terminated sequence of
;; nul-terminated strings. Nothing, for the moment.
(put-u8 line-port 0)
;; File table. For each file that contributes to this
;; compilation unit, a nul-terminated file name string, and a
;; uleb128 for each of directory the file was found in, the
;; modification time, and the file's size in bytes. We pass
;; zero for the latter three fields.
(vlist-fold-right
(lambda (pair seed)
(match pair
((file . code)
(put-bytevector line-port (string->utf8 file))
(put-u8 line-port 0)
(put-uleb128 line-port 0) ; directory
(put-uleb128 line-port 0) ; mtime
(put-uleb128 line-port 0))) ; size
seed)
#f
files)
(put-u8 line-port 0) ; 0 byte terminating file list.
;; Patch prologue length.
(let ((offset (port-position line-port)))
(seek line-port 6 SEEK_SET)
(put-u32 line-port (- offset 10))
(seek line-port offset SEEK_SET))
;; Now write the statement program.
(let ()
(define (extended-op opcode payload-len)
(put-u8 line-port 0) ; extended op
(put-uleb128 line-port (1+ payload-len)) ; payload-len + opcode
(put-uleb128 line-port opcode))
(define (set-address sym)
(define (add-reloc! kind)
(set! line-relocs
(cons (make-linker-reloc kind
(port-position line-port)
0
sym)
line-relocs)))
(match (asm-word-size asm)
(4
(extended-op 2 4)
(add-reloc! 'abs32/1)
(put-u32 line-port 0))
(8
(extended-op 2 8)
(add-reloc! 'abs64/1)
(put-u64 line-port 0))))
(define (end-sequence pc)
(let ((pc-inc (- (asm-pos asm) pc)))
(put-u8 line-port 2) ; advance-pc
(put-uleb128 line-port pc-inc))
(extended-op 1 0))
(define (advance-pc pc-inc line-inc)
(let ((spec (+ (- line-inc base) (* pc-inc range) 10)))
(cond
((or (< line-inc base) (>= line-inc (+ base range)))
(advance-line line-inc)
(advance-pc pc-inc 0))
((<= spec 255)
(put-u8 line-port spec))
((< spec 500)
(put-u8 line-port 8) ; const-advance-pc
(advance-pc (- pc-inc (floor/ (- 255 10) range))
line-inc))
(else
(put-u8 line-port 2) ; advance-pc
(put-uleb128 line-port pc-inc)
(advance-pc 0 line-inc)))))
(define (advance-line inc)
(put-u8 line-port 3)
(put-sleb128 line-port inc))
(define (set-file file)
(put-u8 line-port 4)
(put-uleb128 line-port file))
(define (set-column col)
(put-u8 line-port 5)
(put-uleb128 line-port col))
(set-address '.rtl-text)
(let lp ((in out) (pc 0) (file 1) (line 1) (col 0))
(match in
(()
(when (null? out)
;; There was no source info in the first place. Set
;; file register to 0 before adding final row.
(set-file 0))
(end-sequence pc))
(((pc* file* line* col*) . in*)
(cond
((and (eqv? file file*) (eqv? line line*) (eqv? col col*))
(lp in* pc file line col))
(else
(unless (eqv? col col*)
(set-column col*))
(unless (eqv? file file*)
(set-file file*))
(advance-pc (- pc* pc) (- line* line))
(lp in* pc* file* line* col*)))))))))))
(define (compute-code attr val)
(match attr
('name (string-table-intern! strtab val))
('low-pc val)
('high-pc val)
('producer (string-table-intern! strtab val))
('language (language-name->code val))
('stmt-list val)))
(define (choose-form attr val code)
(cond
((string? val) 'strp)
((eq? attr 'stmt-list) 'sec-offset)
((eq? attr 'low-pc) 'addr)
((exact-integer? code)
(cond
((< code 0) 'sleb128)
((<= code #xff) 'data1)
((<= code #xffff) 'data2)
((<= code #xffffffff) 'data4)
((<= code #xffffffffffffffff) 'data8)
(else 'uleb128)))
(else (error "unhandled case" attr val code))))
(define (add-die-relocation! kind sym)
(set! die-relocs
(cons (make-linker-reloc kind (port-position die-port) 0 sym)
die-relocs)))
(define (write-value code form)
(match form
('data1 (put-u8 die-port code))
('data2 (put-u16 die-port code))
('data4 (put-u32 die-port code))
('data8 (put-u64 die-port code))
('uleb128 (put-uleb128 die-port code))
('sleb128 (put-sleb128 die-port code))
('addr
(match (asm-word-size asm)
(4
(add-die-relocation! 'abs32/1 code)
(put-u32 die-port 0))
(8
(add-die-relocation! 'abs64/1 code)
(put-u64 die-port 0))))
('sec-offset (put-u32 die-port code))
('strp (put-u32 die-port code))))
(define (write-die die)
(match die
((tag ('@ (attrs vals) ...) children ...)
(let* ((codes (map compute-code attrs vals))
(forms (map choose-form attrs vals codes))
(has-children? (not (null? children)))
(abbrev-code (intern-abbrev tag has-children? attrs forms)))
(put-uleb128 die-port abbrev-code)
(for-each write-value codes forms)
(when has-children?
(for-each write-die children)
(put-uleb128 die-port 0))))))
;; Compilation unit header.
(put-u32 die-port 0) ; Length; will patch later.
(put-u16 die-port 4) ; DWARF 4.
(put-u32 die-port 0) ; Abbrevs offset.
(put-u8 die-port (asm-word-size asm)) ; Address size.
(write-die (make-compile-unit-die asm))
;; Terminate the abbrevs list.
(put-uleb128 abbrev-port 0)
(write-sources)
(values (let ((bv (get-die-bv)))
;; Patch DWARF32 length.
(bytevector-u32-set! bv 0 (- (bytevector-length bv) 4)
(asm-endianness asm))
(make-object asm '.debug_info bv die-relocs '()
#:type SHT_PROGBITS #:flags 0))
(make-object asm '.debug_abbrev (get-abbrev-bv) '() '()
#:type SHT_PROGBITS #:flags 0)
(make-object asm '.debug_str (link-string-table! strtab) '() '()
#:type SHT_PROGBITS #:flags 0)
(make-object asm '.debug_loc #vu8() '() '()
#:type SHT_PROGBITS #:flags 0)
(let ((bv (get-line-bv)))
;; Patch DWARF32 length.
(bytevector-u32-set! bv 0 (- (bytevector-length bv) 4)
(asm-endianness asm))
(make-object asm '.debug_line bv line-relocs '()
#:type SHT_PROGBITS #:flags 0)))))
(define (link-objects asm)
(let*-values (;; Link procprops before constants, because it probably
;; interns more constants.
((procprops) (link-procprops asm))
((ro rw rw-init) (link-constants asm))
;; Link text object after constants, so that the
;; constants initializer gets included.
((text) (link-text-object asm))
((frame-maps) (link-frame-maps asm))
((dt) (link-dynamic-section asm text rw rw-init frame-maps))
((symtab strtab) (link-symtab (linker-object-section text) asm))
((arities arities-strtab) (link-arities asm))
((docstrs docstrs-strtab) (link-docstrs asm))
((dinfo dabbrev dstrtab dloc dline) (link-debug asm))
;; This needs to be linked last, because linking other
;; sections adds entries to the string table.
((shstrtab) (link-shstrtab asm)))
(filter identity
(list text ro frame-maps rw dt symtab strtab
arities arities-strtab
docstrs docstrs-strtab procprops
dinfo dabbrev dstrtab dloc dline
shstrtab))))
;;;
;;; High-level public interfaces.
;;;
(define* (link-assembly asm #:key (page-aligned? #t))
"Produce an ELF image from the code and data emitted into @var{asm}.
The result is a bytevector, by default linked so that read-only and
writable data are on separate pages. Pass @code{#:page-aligned? #f} to
disable this behavior."
(link-elf (link-objects asm) #:page-aligned? page-aligned?))