Hi @ll,
compiler-rt implements the Windows-specific routines
compiler-rt/lib/builtins/i386/chkstk.S and
compiler-rt/lib/builtins/x86_64/chkstk.S
See <Developer tools, technical documentation and coding examples | Microsoft Docs;
Their implementation is but LESS THAN optimal: they can
yield upto (stacksize / pagesize) superfluous page accesses
(and thus superfluous page faults)!
As implemented, ALL calls of chkstk() touch ALL pages from
the current "top" of stack to its new "top", which might
become the new stack "limit": on access of the "guard page"
Windows handles the stack growth.
Touching of pages already touched before, ie. above the
current "limit" of the stack, is but NOT necessary!
Properly optimised chkstk() implementations (for ML.EXE
and ML64.EXE respectively), which touch every page only
once, are shown below!
regards
Stefan Kanthak
See <https://godbolt.org/z/1jSn6->
--- sample0.c ---
void foo(int bar) {
int array[234567];
array[234566] = bar;
}
_foo: # @foo
push ebp
mov ebp, esp
mov eax, 938272
call __chkstk
mov eax, dword ptr [ebp + 8]
mov ecx, dword ptr [ebp + 8]
mov dword ptr [ebp - 4], ecx
mov dword ptr [ebp - 938272], eax # 4-byte Spill
add esp, 938272
pop ebp
ret
int main(int argc) {
foo (argc);
foo (argc);
}
--- chkstk.asm (for I386) ---