http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51332
Bug #: 51332
Summary: __sync_add_and_fetch segfaults when -fPIC is enabled
Classification: Unclassified
Product: gcc
Version: 4.1.2
Status: UNCONFIRMED
Severity: major
Priority: P3
Component: c
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: luca.mart...@tin.it
Created attachment 25931
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=25931
preprocessor output
The code generated from compiler intrinsic __sync_add_and_fetch (on a 64bit
value) is erroneous when the -fPIC switch is enabled.
It seems that when the -fPIC switch is enabled, instruction CMPXCHG8B
references register EBX as a base pointer for the memory operand, whereas EBX
must contain part of the value to be incremented.
See a minimal reproducible example in attachment.
We experienced the problem when compiling with the following flags:
gcc version 4.1.2 20080704 (Red Hat 4.1.2-51)
/usr/libexec/gcc/x86_64-redhat-linux/4.1.2/cc1 -E -quiet -v main.c -m32
-march=i686 -fPIC -fworking-directory -fpch-preprocess -o main.i
the generated instruction is
lock cmpxchg8b (%ebx)
and should have been
lock cmpxchg8b (%esi)
we could not reproduce the bug with the gcc 4.4.4
