Question

尝试pclose()以前使用popen()打开的管道时，我遇到了valgrind错误。错误发生在Mac OS X上，但不发生在Linux上。请考虑以下示例：

#include <stdlib.h>
#include <stdio.h>

int main() {
  FILE *fp;
  char buf[4096];

  if (!(fp = popen("ls", "r")))
    exit(-1);

  while (fscanf(fp, "%s", buf) == 1)
    printf("%s\n", buf);

  pclose(fp);

  return 0;
}

我在Mac上遇到以下valgrind错误（OS X 10.6.7，valgrind版本3.6.0），除非我删除pclose()调用：

==21455== Conditional jump or move depends on uninitialised value(s)
==21455==    at 0xB1992: pclose (in /usr/lib/libSystem.B.dylib)
==21455==    by 0x1F16: main (in ./a.out)
==21455== 
==21455== Syscall param wait4(pid) contains uninitialised byte(s)
==21455==    at 0x504FA: wait4 (in /usr/lib/libSystem.B.dylib)
==21455==    by 0x1F16: main (in ./a.out)

但是，我在使用valgrind版本3.5.0的Linux系统上没有出现任何错误。

关于什么可能导致Mac上的错误的任何想法？

更新

启用valgrind中的--track-origins表示问题的根源可能在popen()调用中。与gcc 4.2.1和4.5.3一样。

==4425== Conditional jump or move depends on uninitialised value(s)
==4425==    at 0xB1992: pclose (in /usr/lib/libSystem.B.dylib)
==4425==    by 0x1F18: main (in ./a.out)
==4425==  Uninitialised value was created by a stack allocation
==4425==    at 0xB14C5: popen$UNIX2003 (in /usr/lib/libSystem.B.dylib)
==4425== 
==4425== Syscall param wait4(pid) contains uninitialised byte(s)
==4425==    at 0x504FA: wait4 (in /usr/lib/libSystem.B.dylib)
==4425==    by 0x1F18: main (in ./a.out)
==4425==  Uninitialised value was created by a stack allocation
==4425==    at 0xB14C5: popen$UNIX2003 (in /usr/lib/libSystem.B.dylib)

Answer 1

系统库将未初始化的字节传递给系统调用是很常见的。条件跳转依赖于未初始化的值并不常见，但确实发生了（我的Linux版本中的glibc-2.X.supp在glibc中包含8个抑制）。

因为无论如何你都无法做到这些错误，你应该压制它们。请参阅Valgrind文档中的--gen-suppressions。

Answer 2

报告的问题似乎是系统库的内部问题，而不是代码。

使用MacOS X 10.6.8，Valgrind 3.6.0以及（Apple的）GCC 4.2.1或（我的）GCC 4.6.0，我也没有错误。我从你的代码中得到编译警告（显示4.6.0） - 实际上，我'make'运行命令，makefile包含所有-Wxxx个参数：

$ gcc -g -std=c99 -Wall -Wextra -Wmissing-prototypes -Wstrict-prototypes -Wold-style-definition     vg.c -o vg
vg.c:4:5: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
vg.c: In function ‘main’:
vg.c:4:5: warning: old-style function definition [-Wold-style-definition]
$ valgrind vg
==40593== Memcheck, a memory error detector
==40593== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al.
==40593== Using Valgrind-3.6.0 and LibVEX; rerun with -h for copyright info
==40593== Command: vg
==40593== 
vg
vg.c
vg.dSYM
==40593== 
==40593== HEAP SUMMARY:
==40593==     in use at exit: 4,184 bytes in 2 blocks
==40593==   total heap usage: 6 allocs, 4 frees, 26,848 bytes allocated
==40593== 
==40593== LEAK SUMMARY:
==40593==    definitely lost: 0 bytes in 0 blocks
==40593==    indirectly lost: 0 bytes in 0 blocks
==40593==      possibly lost: 0 bytes in 0 blocks
==40593==    still reachable: 4,184 bytes in 2 blocks
==40593==         suppressed: 0 bytes in 0 blocks
==40593== Rerun with --leak-check=full to see details of leaked memory
==40593== 
==40593== For counts of detected and suppressed errors, rerun with: -v
==40593== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
$ cc --version
i686-apple-darwin10-llvm-gcc-4.2 (GCC) 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2335.9)
Copyright (C) 2007 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ gcc --version
gcc (GCC) 4.6.0
Copyright (C) 2011 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ valgrind --version
valgrind-3.6.0
Localhost JL: uname -a
Darwin localhost 10.8.0 Darwin Kernel Version 10.8.0: Tue Jun  7 16:33:36 PDT 2011; root:xnu-1504.15.3~1/RELEASE_I386 i386
$ otool -L /usr/lib/libSystem.B.dylib
/usr/lib/libSystem.B.dylib:
    /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 125.2.11)
    /usr/lib/system/libmathCommon.A.dylib (compatibility version 1.0.0, current version 315.0.0)

使用-v --gen-suppressions=yes运行时，valgrind会报告更多信息，但仍然没有抑制错误。

Answer 3

此错误在最新的Valgrind SVN源中显示已解决。 Valgrind中的许多内部错误已经解决，以及已知的Apple系统库错误被抑制。

请注意，这是在OS X 10.10.4

上运行的

$ ./vg-in-place ../../test
==55558== Memcheck, a memory error detector
==55558== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==55558== Using Valgrind-3.11.0.SVN and LibVEX; rerun with -h for copyright info
==55558== Command: ../../test
==55558== 
--55558-- ../../test:
--55558-- dSYM directory is missing; consider using --dsymutil=yes
AUTHORS
COPYING
COPYING.DOCS
Makefile
...
vg-in-place
xfree-3.supp
xfree-4.supp
==55558== 
==55558== HEAP SUMMARY:
==55558==     in use at exit: 39,331 bytes in 419 blocks
==55558==   total heap usage: 523 allocs, 104 frees, 68,971 bytes allocated
==55558== 
==55558== LEAK SUMMARY:
==55558==    definitely lost: 0 bytes in 0 blocks
==55558==    indirectly lost: 0 bytes in 0 blocks
==55558==      possibly lost: 0 bytes in 0 blocks
==55558==    still reachable: 0 bytes in 0 blocks
==55558==         suppressed: 39,331 bytes in 419 blocks
==55558== 
==55558== For counts of detected and suppressed errors, rerun with: -v
==55558== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
$ ./vg-in-place --version
valgrind-3.11.0.SVN

在Mac OS X上由pclose（）引起的Valgrind错误

3 个答案: