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I'm reverse engineering some windows application. I came accross with this function that IDA recognized:
call __alloca_probe_16
I'm unable to find any documentation/reference on this function except here. The poster suggests that __alloca_probe is a support routine for the API _alloca() without providing any reference.
I'm just wondering if anyone knows what this function does and where I can find reference to undocumented/internal(?) APIs like this in the future.
This funcion enures that an alloca() call returns a pointer aligned to 16 bytes boundary. You can see the comments in alloca16.asm in Visual C++' CRT sources:
; _alloca_probe_16, _alloca_probe_8 - align allocation to 16/8 byte boundary
;
;Purpose:
; Adjust allocation size so the ESP returned from chkstk will be aligned
; to 16/8 bit boundary. Call chkstk to do the real allocation.
;Entry:
; EAX = size of local frame
;
;Exit:
; Adjusted EAX.
;
;Uses:
; EAX
NB: this comment seems to be stale; the current implementation tail-calls _chkstk, so the allocation (ESP adjustment) happens immediately.
