Still problems with alloca and frame layout on w64 targets

Still problems with alloca and frame layout on w64 targets

[Kai Tietz]

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Hi,

this small c program produces wrong code on x86_64-pc-mingw32. The problem 
here is the call abi w64. For w64 call abi, the last reserved 32 bytes on 
stack are use for vaarg functions to save the incoming arguments from 
register. This works fine as long as there is no alloca call within the 
function calling a vaarg method. The alloca reserves just the stack, but 
does not move the stack clobber region. So by a vaarg call the last 
reserved stack is clobbered.

How and where can I solve this problem?

Thanks in advance,
Kai



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[-- Attachment #2: test.c --]
[-- Type: application/octet-stream, Size: 578 bytes --]

#include <stdio.h>
#include <stdlib.h>
#include <memory.h>
#include <stdarg.h>

void do_zero (int argc, ...)
{
  va_list argp;
  char *c;
  va_start(argp, argc);
  while ((c=va_arg(argp,char *))!=NULL)
    memset(c,0,32);
  va_end (argp);
}

void do_print (const char *fmt, const char *h,int s)
{
  int i;
  for (i=0;h[i]==0 && i<s;i++);
  if (i!=s) abort ();
}

int main (int argc,char **argv)
{
  char *a,*b;
  a = (char *) alloca (argc * 32);
  do_zero (0,a,b,NULL);
  b = (char *) alloca (argc * 32);
  do_print ("a",a,argc * 32);
  do_print ("a",b,argc * 32);
  return 0;
}

Re: Still problems with alloca and frame layout on w64 targets

[Kai Tietz]

[-- Attachment #1: Type: text/plain, Size: 719 bytes --]

> Hi,
> 
> this small c program produces wrong code on x86_64-pc-mingw32. The 
problem 
> here is the call abi w64. For w64 call abi, the last reserved 32 bytes 
on 
> stack are use for vaarg functions to save the incoming arguments from 
> register. This works fine as long as there is no alloca call within the 
> function calling a vaarg method. The alloca reserves just the stack, but 

> does not move the stack clobber region. So by a vaarg call the last 
> reserved stack is clobbered.
> 
> How and where can I solve this problem?

Sorry I attached wrong testcase

Thanks in advance,
Kai



|  (\_/)  This is Bunny. Copy and paste Bunny
| (='.'=) into your signature to help him gain
| (")_(") world domination.

[-- Attachment #2: test.c --]
[-- Type: application/octet-stream, Size: 616 bytes --]

#include <stdio.h>
#include <stdlib.h>
#include <memory.h>
#include <stdarg.h>

void do_zero (int argc, ...)
{
  va_list argp;
  char *c;
  va_start(argp, argc);
  while ((c=va_arg(argp,char *))!=NULL)
    memset(c,0,argc);
  va_end (argp);
}

void do_print (const char *fmt, const char *h,int s)
{
  int i;
  for (i=0;h[i]==0 && i<s;i++);
  if (i!=s) abort ();
}

int main (int argc,char **argv)
{
  char *a,*b;
  a = (char *) alloca (argc * 32);
  do_zero (argc * 32,a,NULL);
  b = (char *) alloca (argc * 32);
  do_zero (argc * 32,b,NULL);
  do_print ("a",a,argc * 32);
  do_print ("a",b,argc * 32);
  return 0;
}