It is strange that using printf that doesn't use any variables disables abort.
$ cat test2.c
#include <stdlib.h>
#include <stdio.h>
int
main (void)
{
int a = 0x12345678;
short *b = (short *) &a;
b[1] = 0;
printf("\n");
if (a == 0x12345678)
abort();
exit(0);
}
$ gcc -fstrict-aliasing -O2 -Wall test2.c
test2.c: In function main:
test2.c:8: warning: likely type-punning may break strict-aliasing rules: object
*{unknown} of main type short int is referenced at or around test2.c:8 and
may be aliased to object a of main type int which is referenced at or
around test2.c:6.
$ ./a.out
$
The conditional jump is activated when printf is using:
@@ -7,9 +7,16 @@
.LFB20:
subq $24, %rsp
.LCFI0:
+ movl $10, %edi
movl $305419896, 20(%rsp)
movw $0, 22(%rsp)
+ call putchar
+ cmpl $305419896, 20(%rsp)
+ jne .L2
call abort
+.L2:
+ xorl %edi, %edi
+ call exit
.LFE20:
.size main, .-main
.section .eh_frame,"a",@progbits
$ gcc -v
Using built-in specs.
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla
--enable-bootstrap --enable-shared --enable-threads=posix
--enable-checking=release --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada --enable-java-awt=gtk
--disable-dssi --enable-plugin
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre
--enable-libgcj-multifile --enable-java-maintainer-mode
--with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib
--with-cpu=generic --build=x86_64-redhat-linux
Thread model: posix
gcc version 4.3.2 20081105 (Red Hat 4.3.2-7) (GCC)
--
Summary: printf changes fstrict-aliasing behaviour
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: anvoebugz at gmail dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39268
