optimization/7690: gcc 2.95.3: argument destroyed under -O2 on IA32
torek@bsdi.com
torek@bsdi.com
Thu Aug 22 15:06:00 GMT 2002
>Number: 7690
>Category: optimization
>Synopsis: gcc 2.95.3: argument destroyed under -O2 on IA32
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: unassigned
>State: open
>Class: sw-bug
>Submitter-Id: net
>Arrival-Date: Thu Aug 22 15:06:00 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator: torek@bsdi.com
>Release: gcc 2.95.3
>Organization:
>Environment:
BSD/OS 4.3
>Description:
The stripped-down C code below generates IA32 assembly that destroys the "name" parameter before making another call, but only when using -O2.
This code is simplified from a real program (squid) and no longer does anything useful on its own, so you must look at the generated assembly.
I was hoping this is a known bug with a known fix that I can find somewhere so as to patch it.
>How-To-Repeat:
typedef unsigned long long off_t;
typedef unsigned int size_t;
off_t f1(char *buf, size_t sz, const char *name);
void f2(int);
void bug(char *buf, size_t sz, const char *name, unsigned type)
{
off_t off;
off = f1(buf, sz, name);
memcpy(buf + off, &type, sizeof(type));
f2(off <= sz);
}
compile with -O2, examine assembly, note this section:
movl 8(%ebp),%edi
movl 12(%ebp),%eax
xorl %edx,%edx
movl %eax,12(%ebp)
movl %edx,16(%ebp)
note that 16(%ebp) used to hold the parameter "name" before this last movl, which (since %edx is now 0) clobbers it.
Using -O1 -fexpensive-optimizations appears to suffice to trigger the problem (but -O1 alone does not).
>Fix:
>Release-Note:
>Audit-Trail:
>Unformatted:
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