[Sablevm-developer] gcc bug or not?

[David <db...@cs...>]

Hi,

I have this code structure in sablevm.c and it was seg faulting
on OS X/ppc and I noticed recently that it segfaults also on
Linux/x86 but not Linux/ppc.  This occurs when SableVM is not
compiled with debugging code.

	  case ARG_JIT_OPTION:
	    {
	      const char *str =3D NULL;
	      int len;

              if (...) {

                ...

              } else if (strncmp
		   (argument, str =3D "intr-count=3D", len =3D strlen (str)) =3D=3D 0) =
{

                ...

              } else {
                ...
              }

It segfaults in strlen.  The reg containing str on x86 was containing NUL=
L.

So either the evaluation order of the arguments in C is undefined (gcc
gives no warning for that code) and that the 3rd arg is computed before
the 2nd arg or there is a bug in gcc such that gcc cannot compute the
dependency and reverse them.

This occurs only in non-debugging mode.

Any suggestion/comments from C and gcc experts?

I will work around it by changing the code structure.

My gcc versions are:

x86: 3.3.3 20040110 (prerelease) (Debian)
OS X/ppc: gcc (GCC) 3.1 20020420 (prerelease)
Linux/ppc: gcc-3.3 (GCC) 3.3.2 (Debian)


David

---

David B=E9langer
Graduate Student
School of Computer Science
McGill University
Office: MC226

Web page:   http://www.cs.mcgill.ca/~dbelan2/
Public key: http://www.cs.mcgill.ca/~dbelan2/public_key.txt