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Update frames.h comments.

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* libguile/frames.h: Update to match reality.
This commit is contained in:
Andy Wingo 2018-07-23 11:23:18 +02:00
parent 950a762dc2
commit 4b7af0b7fd
1 changed files with 6 additions and 10 deletions
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16
libguile/frames.h
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@ -40,7 +40,7 @@
------------------ ------------------
| ... | | ... |
+==============================+ <- fp + 2 = SCM_FRAME_PREVIOUS_SP (fp) +==============================+ <- fp + 3 = SCM_FRAME_PREVIOUS_SP (fp)
| Dynamic link | | Dynamic link |
+------------------------------+ +------------------------------+
| Virtual return address (vRA) | | Virtual return address (vRA) |
@ -59,7 +59,7 @@
The stack grows down. The stack grows down.
The calling convention is that a caller prepares a stack frame The calling convention is that a caller prepares a stack frame
consisting of the saved FP, the saved virtual return addres, and the consisting of the saved FP, the saved virtual return address, and the
saved machine return address of the calling function, followed by the saved machine return address of the calling function, followed by the
procedure and then the arguments to the call, in order. Thus in the procedure and then the arguments to the call, in order. Thus in the
beginning of a call, the procedure being called is in slot 0, the beginning of a call, the procedure being called is in slot 0, the
@ -73,14 +73,10 @@
popping the stack pointer during the call's extent. popping the stack pointer during the call's extent.
When a program returns, it returns its values in the slots starting When a program returns, it returns its values in the slots starting
from local 1, as if the values were arguments to a tail call. We from local 0. The callee resets the stack pointer to point to the
start from 1 instead of 0 for the convenience of the "values" builtin last value. In this way the caller knows how many values there are:
function, which can just leave its arguments in place. it's the number of words between the stack pointer and the slot at
which the caller placed the procedure.
The callee resets the stack pointer to point to the last value. In
this way the caller knows how many values there are: it's the number
of words between the stack pointer and the slot at which the caller
placed the procedure.
After checking that the number of values returned is appropriate, the After checking that the number of values returned is appropriate, the
caller shuffles the values around (if needed), and resets the stack caller shuffles the values around (if needed), and resets the stack