http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55513
Bug #: 55513
Summary: Incorrect snprintf folding when building with
-std=c++0x
Classification: Unclassified
Product: gcc
Version: 4.7.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: [email protected]
ReportedBy: [email protected]
Using the following program:
#include <cstdio>
#include <iostream>
int main() {
char str[10];
const int strLength = snprintf(str, sizeof(str), "Hello");
std::cout << strLength << ':' << str << std::endl;
return 0;
}
When built with the following command:
g++ test_snprintf.cc -O0 -g3 -std=c++0x
The output of running it is:
5:
instead of:
5: Hello
The program will work fine if either of the following changes are made
1. -std=c++0x is removed from the build command line.
2. The const is removed from the definition of the variable strLength
Here's a disassembly of main() up until the call to ostream::operator<<, when
built with -std=c++0x:
0x0000000000400a6c <+0>: push %rbp
0x0000000000400a6d <+1>: mov %rsp,%rbp
0x0000000000400a70 <+4>: sub $0x30,%rsp
0x0000000000400a74 <+8>: mov %fs:0x28,%rax
0x0000000000400a7d <+17>: mov %rax,-0x8(%rbp)
0x0000000000400a81 <+21>: xor %eax,%eax
0x0000000000400a83 <+23>: movl $0x5,-0x24(%rbp)
0x0000000000400a8a <+30>: mov $0x5,%esi
0x0000000000400a8f <+35>: mov $0x6010a0,%edi
0x0000000000400a94 <+40>: callq 0x4008a0 <_ZNSolsEi@plt>
0x0000000000400a99 <+45>: mov $0x3a,%esi
0x0000000000400a9e <+50>: mov %rax,%rdi
0x0000000000400aa1 <+53>: callq 0x4008e0
<_ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_c@plt>
Here's a disassembly of main() up until the call to ostream::operator<<, when
built without -std=c++0x _or_ when the const is removed (same result):
0x0000000000400a6c <+0>: push %rbp
0x0000000000400a6d <+1>: mov %rsp,%rbp
0x0000000000400a70 <+4>: sub $0x30,%rsp
0x0000000000400a74 <+8>: mov %fs:0x28,%rax
0x0000000000400a7d <+17>: mov %rax,-0x8(%rbp)
0x0000000000400a81 <+21>: xor %eax,%eax
0x0000000000400a83 <+23>: lea -0x20(%rbp),%rax
0x0000000000400a87 <+27>: movl $0x6c6c6548,(%rax)
0x0000000000400a8d <+33>: movw $0x6f,0x4(%rax)
0x0000000000400a93 <+39>: movl $0x5,-0x24(%rbp)
0x0000000000400a9a <+46>: mov -0x24(%rbp),%eax
0x0000000000400a9d <+49>: mov %eax,%esi
0x0000000000400a9f <+51>: mov $0x6010a0,%edi
0x0000000000400aa4 <+56>: callq 0x4008a0 <_ZNSolsEi@plt>
0x0000000000400aa9 <+61>: mov $0x3a,%esi
0x0000000000400aae <+66>: mov %rax,%rdi
0x0000000000400ab1 <+69>: callq 0x4008e0
<_ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_c@plt>
OS Version: Ubuntu 12.10
uname -a output:
Linux desktop 3.5.0-18-generic #29-Ubuntu SMP Fri Oct 19 10:26:51 UTC 2012
x86_64 x86_64 x86_64 GNU/Linux
gcc --version output:
gcc (Ubuntu/Linaro 4.7.2-2ubuntu1) 4.7.2
