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* [Bug c/55746] New: vfprintf behaves differently variable on stack vs const argument.
@ 2012-12-19 23:40 lbana at hotmail dot com
2012-12-19 23:44 ` [Bug c/55746] " pinskia at gcc dot gnu.org
0 siblings, 1 reply; 2+ messages in thread
From: lbana at hotmail dot com @ 2012-12-19 23:40 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55746
Bug #: 55746
Summary: vfprintf behaves differently variable on stack vs
const argument.
Classification: Unclassified
Product: gcc
Version: 4.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: lbana@hotmail.com
Here is the test code that behaves differently w.r.t vfprintf. In one case it
prints the string where as in other case it crashes.
#include <stdarg.h>
#include <stdio.h>
int main(int argc, const char **argv)
{
const char *var = "Test VarArg\n";
asm("nop");
asm("nop");
vfprintf(stdout, "TestMe\n", 0);
asm("nop");
asm("nop");
fflush(stdout);
asm("nop");
asm("nop");
vfprintf(stdout, var, 0);
asm("nop");
asm("nop");
fflush(stdout);
return 0;
}
#gcc -g -o t3 t3.c
#./t3
TestMe
Segfault
In first case vfprintf is optimized with _fwrite in the second case it uses
_vfprintf and crashes probably in va_copy.
thanks in advance.
lb
^ permalink raw reply [flat|nested] 2+ messages in thread
* [Bug c/55746] vfprintf behaves differently variable on stack vs const argument.
2012-12-19 23:40 [Bug c/55746] New: vfprintf behaves differently variable on stack vs const argument lbana at hotmail dot com
@ 2012-12-19 23:44 ` pinskia at gcc dot gnu.org
0 siblings, 0 replies; 2+ messages in thread
From: pinskia at gcc dot gnu.org @ 2012-12-19 23:44 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55746
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution| |INVALID
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-12-19 23:44:14 UTC ---
And this is not a bug really. GCC is optimizing the first one to fwrite but
not the second one since it does not see the constant string in the first case.
Also this code is undefined as the varargs that you passed to vfprintf is not
a real one.
^ permalink raw reply [flat|nested] 2+ messages in thread
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2012-12-19 23:40 [Bug c/55746] New: vfprintf behaves differently variable on stack vs const argument lbana at hotmail dot com
2012-12-19 23:44 ` [Bug c/55746] " pinskia at gcc dot gnu.org
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