Red Hat Bugzilla – Bug 396921
gcc 4.1.2 produces bad code
Last modified: 2008-06-16 22:53:24 EDT
Description of problem:
Gcc creates invalid code from the attached files by essentially trying to
dereference an integer as if it were a pointer:
movl nonlin@GOT(%ebx), %edi #,
movl nlin@GOT(%ebx), %esi #,
movl gradf@GOT(%ebx), %edx #, tmp1129
movl (%ecx), %ecx # o8opti_yx,
movl $1, -64(%ebp) #, i.5726
movl (%esi), %eax # nlin, nlin
movl gres@GOT(%ebx), %esi #,
movl %ecx, -168(%ebp) #,
movl (%edi), %ecx # nonlin,
movl n@GOT(%ebx), %edi #,
movl (%edx), %edx # gradf,
movl (%esi), %esi # gres,
addl %eax, %ecx # nlin,
movl (%edi), %edi # n,
movl %ecx, -172(%ebp) #,
movl %esi, -260(%ebp) #,
movl %edx, -264(%ebp) #,
addl (%edi), %eax # nonlin, nlin
The last line here causes a segmentation fault. The bug only shows up with -fPIC
-O2 (or higher).
Version-Release number of selected component (if applicable):
On suitable code always, but very sensitive to global characteristics of the code.
Steps to Reproduce:
1. Compile the attached files using
gcc -g -Wall -fPIC -O2 f1.c f2.c
2. Run the resulting a.out (optionally under gdb)
Segmentation fault on line 974 of f1.c, which is:
for (i = 1 ; i <= n ; i++)
Program runs without problems
The test case is rather long, because the bug is very evasive. Even removing
code long after the affected location will often make the bug disappear.
Created attachment 267611 [details]
First demonstration file
Created attachment 267621 [details]
Second demonstration file
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