llvm dev - Apr 2014 - [LLVMdev] correctness in localized global variable between setjmp and longjmp

I noticed that c code below failed with -O3 : 

 

#include <setjmp.h>

#include <stdio.h>

 

static int cnt;

 

int main(){

  int var;

  jmp_buf buffer;

  cnt = 0;

 

  if ((var = setjmp(buffer)) == 0) {

    printf(" if true, var: %d, .count:%d , increase count !\n",var,
cnt);

    cnt++;

    longjmp(buffer, 2);

  } else {

    if (cnt == 1)

      printf(" Pass      var: %d, .count:%d \n",var, cnt);

    else

      printf(" Fail !!!  var: %d, .count:%d \n",var, cnt);

  }

  return 0;

}

 

The documentation of setjmp/longjmp says that the values of objects of
automatic storage duration which are local to the function containing the
invocation of the corresponding setjmp() which do not have
volatile-qualified type and which are changed between the setjmp()
invocation and longjmp() call are indeterminate.

 

Even though "cnt" is a global variable, above c code failed because
the
globalopt pass localizes the global value (cnt) in main(), causing that the
value of the global variable becomes indeterminate between setjmp() and
longjmp. I believe the globalopt pass need to check this case before
localizing global variables. Is there any better solution about it?

 

Thanks,

Balaram

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On 28 April 2014 15:01, Balaram Makam <bmakam at codeaurora.org>
wrote:
> I noticed that c code below failed with -O3 :
>
>
>
> #include <setjmp.h>
>
> #include <stdio.h>
>
>
>
> static int cnt;
>
>
>
> int main(){
>
>   int var;
>
>   jmp_buf buffer;
>
>   cnt = 0;
>
>
>
>   if ((var = setjmp(buffer)) == 0) {
>
>     printf(" if true, var: %d, .count:%d , increase count
!\n",var, cnt);
>
>     cnt++;
>
>     longjmp(buffer, 2);
>
>   } else {
>
>     if (cnt == 1)
>
>       printf(" Pass      var: %d, .count:%d \n",var, cnt);
>
>     else
>
>       printf(" Fail !!!  var: %d, .count:%d \n",var, cnt);
>
>   }
>
>   return 0;
>
> }
>
>
>
> The documentation of setjmp/longjmp says that the values of objects of
> automatic storage duration which are local to the function containing the
> invocation of the corresponding setjmp() which do not have
> volatile-qualified type and which are changed between the setjmp()
> invocation and longjmp() call are indeterminate.
>
>
>
> Even though “cnt” is a global variable, above c code failed because the
> globalopt pass localizes the global value (cnt) in main(), causing that the
> value of the global variable becomes indeterminate between setjmp() and
> longjmp. I believe the globalopt pass need to check this case before
> localizing global variables. Is there any better solution about it?
No, looks like it has to check it.

This is a very specific optimization, but it looks like it is still
important in old benchmarks.

Cheers,
Rafael

Balaram,
Perhaps you should file a bug report here:
http://llvm.org/bugs/

 Chad
> I noticed that c code below failed with -O3 :
>
>
>
> #include <setjmp.h>
>
> #include <stdio.h>
>
>
>
> static int cnt;
>
>
>
> int main(){
>
>   int var;
>
>   jmp_buf buffer;
>
>   cnt = 0;
>
>
>
>   if ((var = setjmp(buffer)) == 0) {
>
>     printf(" if true, var: %d, .count:%d , increase count
!\n",var, cnt);
>
>     cnt++;
>
>     longjmp(buffer, 2);
>
>   } else {
>
>     if (cnt == 1)
>
>       printf(" Pass      var: %d, .count:%d \n",var, cnt);
>
>     else
>
>       printf(" Fail !!!  var: %d, .count:%d \n",var, cnt);
>
>   }
>
>   return 0;
>
> }
>
>
>
> The documentation of setjmp/longjmp says that the values of objects of
> automatic storage duration which are local to the function containing the
> invocation of the corresponding setjmp() which do not have
> volatile-qualified type and which are changed between the setjmp()
> invocation and longjmp() call are indeterminate.
>
>
>
> Even though "cnt" is a global variable, above c code failed
because the
> globalopt pass localizes the global value (cnt) in main(), causing that
> the
> value of the global variable becomes indeterminate between setjmp() and
> longjmp. I believe the globalopt pass need to check this case before
> localizing global variables. Is there any better solution about it?
>
>
>
> Thanks,
>
> Balaram
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>

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