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* [Bug c++/55513] New: Incorrect snprintf folding when building with -std=c++0x
@ 2012-11-28 10:04 gnobal at hotmail dot com
  2012-11-28 10:05 ` [Bug c++/55513] " gnobal at hotmail dot com
                   ` (12 more replies)
  0 siblings, 13 replies; 14+ messages in thread
From: gnobal at hotmail dot com @ 2012-11-28 10:04 UTC (permalink / raw)
  To: gcc-bugs


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: unassigned@gcc.gnu.org
        ReportedBy: gnobal@hotmail.com


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


^ permalink raw reply	[flat|nested] 14+ messages in thread
end of thread, other threads:[~2012-12-12  9:57 UTC | newest]

Thread overview: 14+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2012-11-28 10:04 [Bug c++/55513] New: Incorrect snprintf folding when building with -std=c++0x gnobal at hotmail dot com
2012-11-28 10:05 ` [Bug c++/55513] " gnobal at hotmail dot com
2012-11-28 10:19 ` [Bug c++/55513] [4.7 Regression] " redi at gcc dot gnu.org
2012-11-28 12:35 ` rguenth at gcc dot gnu.org
2012-11-28 14:26 ` [Bug c++/55513] [4.7/4.8 " jakub at gcc dot gnu.org
2012-11-28 15:15 ` jakub at gcc dot gnu.org
2012-11-28 15:51 ` jakub at gcc dot gnu.org
2012-12-05 17:10 ` aldyh at gcc dot gnu.org
2012-12-06 16:16 ` rguenth at gcc dot gnu.org
2012-12-06 21:06 ` aldyh at gcc dot gnu.org
2012-12-07  5:21 ` jason at gcc dot gnu.org
2012-12-08  3:13 ` aldyh at gcc dot gnu.org
2012-12-08  3:14 ` aldyh at gcc dot gnu.org
2012-12-12  9:57 ` pluto at agmk dot net

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