The problem...
The following program produces incorrect results on a Linux x86 system when
compiled with gcc v3.4.2 (and 3.4.1) with full optimizations. The program is
supposed to print 0xFFFF, but instead produces random results (seems to be a
stack corruption problem).
The source...
#include <inttypes.h>
#include <iostream>
#include <iomanip>
#define BUG
using namespace std;
class A
{
public:
A () :
valid_mask_(0x00000000FFFFFFFFull),
size_(0x000000000000FFFFull)
{}
uint64_t calc(uint64_t value) const {
#ifdef BUG
return valid_mask_ & (value | size_);
#else
// This code will never expose the bug
uint64_t tmp = valid_mask_ & (value | size_);
return tmp;
#endif
}
private:
uint64_t valid_mask_;
uint64_t size_;
};
uint32_t CheckStuff()
{
A a;
uint64_t value = a.calc(0);
#ifdef BUG
// This code will expose the bug iff BUG is defined for calc()
cout << "0x" << hex << setfill('0') << value << endl;
#else
// This code will never expose the bug
cout << "0x" << hex << value << endl;
#endif
if(value == 0xffff) {
return 0;
}
else {
return 1;
}
}
int main()
{
return CheckStuff();
}
The build line...
gcc-3.4.1 -v -W -Wall -O3 -g2 gcc_bug.cpp
The results (it's purely random, but here's an example)...
0x8048978bfffbb68
What it should print...
0xFFFF
Observations...
- Take out the -O3 (-O0) and it works
- This program works just fine on Solaris no matter how you compile it
- This program works with gcc 3.3.X, gcc 3.2.X and (shudder) 2.95
- Take out setfill('0') and it works
- Keep setfill('0') in the cout statement and return a tmp for the inline
calc() function and it works
Compiler/system info...
system type:
Linux x86 (RedHat Enterprise 3)
gcc -v output:
--enable-shared --with-ld=/<blah>/gnu-gcc-3.4.1-binutils-2.13.2.1/i686-pc-
linux2.4/bin/ld
--with-as=/<blah>/gnu-gcc-3.4.1-binutils-2.13.2.1/i686-pc-linux2.4/bin/as
--with-nm=/<blah>/gnu-gcc-3.4.1-binutils-2.13.2.1/i686-pc-linux2.4/bin/nm
--enable-languages=c,c++,java --disable-nls
Thread model: posix
gcc version 3.4.1
/<blah>/gnu-gcc-3.4.1-binutils-2.13.2.1/i686-pc-linux2.4/libexec/gcc/i686-pc-
linux-gnu/3.4
.1/cc1plus -quiet -v -D_GNU_SOURCE gcc_bug.cpp -quiet -dumpbase gcc_bug.cpp
-mtune=pentiumpro -auxbase gcc_bug -g2 -O0 -W -Wall -version -o /tmp/cc82jgXc.s
ignoring nonexistent directory
"/<blah>/gnu-gcc-3.4.1-binutils-2.13.2.1/i686-pc-linux2.4/lib/gcc/i686-pc-linux-
gnu/3.4.1/
../../../../i686-pc-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/<blah>/gnu-gcc-3.4.1-binutils-2.13.2.1/i686-pc-linux2.4/lib/gcc/i686-pc-linux-
gnu/3.4.1/.
./../../../include/c++/3.4.1
/<blah>/gnu-gcc-3.4.1-binutils-2.13.2.1/i686-pc-linux2.4/lib/gcc/i686-pc-linux-
gnu/3.4.1/.
./../../../include/c++/3.4.1/i686-pc-linux-gnu
/<blah>/gnu-gcc-3.4.1-binutils-2.13.2.1/i686-pc-linux2.4/lib/gcc/i686-pc-linux-
gnu/3.4.1/.
./../../../include/c++/3.4.1/backward
/usr/local/include
/<blah>/gnu-gcc-3.4.1-binutils-2.13.2.1/i686-pc-linux2.4/include
/<blah>/gnu-gcc-3.4.1-binutils-2.13.2.1/i686-pc-linux2.4/lib/gcc/i686-pc-linux-
gnu/3.4.1/i
nclude
/usr/include
End of search list.
GNU C++ version 3.4.1 (i686-pc-linux-gnu)
compiled by GNU C version 3.4.1.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
/<blah>/gnu-gcc-3.4.1-binutils-2.13.2.1/i686-pc-linux2.4/bin/as -V -Qy -o /tmp/
cc15JK08.o
/tmp/cc82jgXc.s
GNU assembler version 2.13.2.1 (i686-pc-linux-gnu) using BFD version 2.13.2.1
/<blah>/gnu-gcc-3.4.1-binutils-2.13.2.1/i686-pc-linux2.4/libexec/gcc/i686-pc-
linux-gnu/3.4
.1/collect2 --eh-frame-hdr -m elf_i386 -dynamic-linker /lib/ld-linux.so.2 -rpath
/<blah>/gnu-gcc-3.4.1-binutils-2.13.2.1/i686-pc-linux2.4/lib /usr/lib/crt1.o
/usr/lib/crti.o
/<blah>/gnu-gcc-3.4.1-binutils-2.13.2.1/i686-pc-linux2.4/lib/gcc/i686-pc-linux-
gnu/3.4.1/c
rtbegin.o
-L/<blah>/gnu-gcc-3.4.1-binutils-2.13.2.1/i686-pc-linux2.4/lib/gcc/i686-pc-
linux-gnu/3.4.1
-L/<blah>/gnu-gcc-3.4.1-binutils-2.13.2.1/i686-pc-linux2.4/lib/gcc/i686-pc-
linux-gnu/3.4.1
/../../../../i686-pc-linux-gnu/lib
-L/<blah>/gnu-gcc-3.4.1-binutils-2.13.2.1/i686-pc-linux2.4/lib/gcc/i686-pc-
linux-gnu/3.4.1
/../../.. /tmp/cc15JK08.o -lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc
/<blah>/gnu-gcc-3.4.1-binutils-2.13.2.1/i686-pc-linux2.4/lib/gcc/i686-pc-linux-
gnu/3.4.1/c
rtend.o /usr/lib/crtn.o
--
Summary: setfill coupled with inline function: incorrect results
on Linux x86
Product: gcc
Version: 3.4.2
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: knutejunk at austin dot rr dot com
CC: gcc-bugs at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18084
