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64KB segment alignment

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* module/system/vm/linker.scm (*lcm-page-size*): Rename
  from *page-size*, change to 64 KB.
* libguile/loader.c (load_thunk_from_memory): Only require page size
  alignment, knowing that although Guile might emit ELF with 64k
  alignment, it only really needs page alignment.
This commit is contained in:
Andy Wingo 2017-03-08 22:39:29 +01:00
parent 8157c2a3ac
commit c62f0b0256
2 changed files with 50 additions and 4 deletions
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15
libguile/loader.c
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@ -420,7 +420,18 @@ load_thunk_from_memory (char *data, size_t len, int is_read_only)
if (dynamic_segment < 0)
ABORT ("no PT_DYNAMIC segment");
if (!IS_ALIGNED ((scm_t_uintptr) data, alignment))
/* The ELF images that Guile currently emits have segments that are
aligned on 64 KB boundaries, which might be larger than the actual
page size (usually 4 KB). However Guile doesn't actually use the
absolute addresses at all. All Guile needs is for the loaded image
to be able to make the data section writable (for the mmap path),
and for that the segment just needs to be page-aligned, and a page
is always bigger than Guile's minimum alignment. Since we know
(for the mmap path) that the base _is_ page-aligned, we proceed
ahead even if the image alignment is greater than the page
size. */
if (!IS_ALIGNED ((scm_t_uintptr) data, alignment)
&& !IS_ALIGNED (alignment, page_size))
ABORT ("incorrectly aligned base");
/* Allow writes to writable pages. */
@ -433,7 +444,7 @@ load_thunk_from_memory (char *data, size_t len, int is_read_only)
continue;
if (ph[i].p_flags == PF_R)
continue;
if (ph[i].p_align != page_size)
if (ph[i].p_align < page_size)
continue;
if (mprotect (data + ph[i].p_vaddr,