Okie,
I think I see the problem. Since I use pushfl and popfl which modify the esp,
there is a problem when the inline asm returns to C code. GCC has no way of
knowing that the esp has been modified, so any accesses it does based on esp
would be wrong.
Even though I specify that esp has been modified, I don't think GCC takes that
into account. Is there any way I can tell GCC that I have modified the esp by a
certain value?
Thanks,
Yamin
Quoting y2bismil@xxxxxxxxxxxxxxxxxxxx:
>
>
> Hi all,
>
> Okay, this is the issue. I've isolated it way down to some very basic
> functionality, and made a reasonable test bed. I'll post the code below.
>
> When MYINLINE = 1, then the program executes correctly. When MYINLINE is 0,
> then it stops with a single step exception. I was stepping through the code
> and
> from my understanding there is something definitely wrong when a function
> call
> is made instead of the inline code. Bare in mind, my understaind could be
> what
> is wrong :)
>
> >From my understand this is what happens.
>
> pushf - pushes the eflags onto the stack, decrements esp
> mymemcpy - simple memcpy
> popf - pops the eflags from the stack into the eflgs register, increments
> esp
>
> This is basically the program below. When the inlining is not used, for
> some
> reason, the stack gets corrupted. When the variables to be passed into
> memcpy
> are done, they overwrite the location where the eflags register was stored
> (from
> the pushf). This then causes some things to mess up. When inlining is used.
>
> this nicely does not happen.
>
> I always hesitate to say bug as its probably something i'm not specifying or
> some misunderstanding.
> Any ideas?
>
> Yamin
>
>
> *****************************************************
> main.cpp
> *****************************************************
> #include <io.h>
> #include <stdio.h>
>
> #if 0
> #include "chead.h"
> #else
> #define KS_DISABLE() \
> __asm__ __volatile__ ( \
> "pushfl;" \
> : \
> : \
> : "memory", "%esp");
>
> #define KS_ENABLE() \
> __asm__ __volatile__ ( \
> "popfl;" \
> : \
> : \
> : "memory", "%esp");
>
> char * mymemcpy(void *dv, void *sv, int num)
> {
> char * d = (char*)dv;
> char * s = (char*)sv;
> int i;
>
> for( i = 0; i < num; i++) *d++ = *s++;
>
> }
>
>
> #endif
>
>
>
> #define MYINLINE 1
> int main()
> {
> #if MYINLINE
> char *d;
> char *s;
> int i;
> #endif
> char mysrc[] = "HELLO YAMIN\r\n";
> char mydst[32];
> printf ("starting popf test\r\n");
> KS_DISABLE();
> #if MYINLINE
> d = (char*) mydst;
> s = (char*) mysrc;
> for( i = 0; i < sizeof(mysrc); i++) *d++ = *s++;
> #else
> mymemcpy( mydst, mysrc, sizeof(mysrc) );
> #endif
> KS_ENABLE();
> printf ("ending popf test: %s\r\n", mydst);
> }
> *****************************************************
>
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