Undefined reference to posix_memalign using mingw3

问题:

I'm using Debian Squeeze, cross compiling for windows targets using mingw32.

For a Linux target, I can use posix_memalign to allocate aligned memory.

I can't seem to find a way to get this to work for windows targets; I get errors about undefined references. I have tried several alternative functions, to no avail.

Example Code:

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

int main(void)
{
    char *foo;

    /* works on linux */
    posix_memalign(&foo, 1024, 1024);

    /* deprecated linux */
    memalign(1024, 1024);
    valloc(1024);

    /* should work on windows only */
    _aligned_malloc(1024, 1024);
}

Example output for a Linux target (expected):

ben@debian6400:~/folder$ gcc --version
gcc (Debian 4.4.5-8) 4.4.5

ben@debian6400:~/folder$ gcc -std=c99 test.c
test.c: In function ‘main’:
test.c:11: warning: implicit declaration of function ‘posix_memalign’
test.c:18: warning: implicit declaration of function ‘_aligned_malloc’
/tmp/ccPwPLsW.o: In function `main':
test.c:(.text+0x55): undefined reference to `_aligned_malloc'
collect2: ld returned 1 exit status

Example output for a Windows target -- note that all four functions are undefined

ben@debian6400:~/folder$ i586-mingw32msvc-gcc --version
i586-mingw32msvc-gcc (GCC) 4.4.4

ben@debian6400:~/folder$ i586-mingw32msvc-gcc -std=c99 test.c
test.c: In function ‘main’:
test.c:14: warning: implicit declaration of function ‘posix_memalign’
test.c:17: warning: implicit declaration of function ‘memalign’
test.c:18: warning: implicit declaration of function ‘valloc’
test.c:21: warning: implicit declaration of function ‘_aligned_malloc’
/tmp/ccpH5Dsj.o:test.c:(.text+0x26): undefined reference to `_posix_memalign'
/tmp/ccpH5Dsj.o:test.c:(.text+0x3a): undefined reference to `_memalign'
/tmp/ccpH5Dsj.o:test.c:(.text+0x46): undefined reference to `_valloc'
/tmp/ccpH5Dsj.o:test.c:(.text+0x5a): undefined reference to `__aligned_malloc'
collect2: ld returned 1 exit status

Any ideas?

回答1:

You should be able to use _aligned_malloc. Other functions can be missing in mingw.

• Update your mingw. It should work in 4.6.2.
• Try __mingw_aligned_malloc instead.

• Include your headers in this order:

  #include <stdlib.h>
  #include <intrin.h>
  #include <malloc.h>
  #include <windows.h>
  

• _aligned_malloc/_aligned_free is just a simple wrapper around malloc/free. If everything else fails, you should be able to write it yourself.

回答2:

The GNU page for Gnulib says this function is missing on mingw platform and they suggest to use Gnulib pagealign_alloc function on these platforms.

(8.632, posix_memalign) This function is missing on some platforms: MacOS X 10.5, FreeBSD 6.0, NetBSD 3.0, OpenBSD 3.8, Minix 3.1.8, AIX 5.1, HP-UX 11, IRIX 6.5, OSF/1 5.1, Solaris 10, Cygwin 1.5.x, mingw, MSVC 9, Interix 3.5, BeOS.

and

The Gnulib module pagealign_alloc provides a similar API that returns memory aligned on a system page boundary.

http://www.gnu.org/software/gnulib/manual/html_node/posix_005fmemalign.html

Note that on C11, there is a new function named align_alloc where the alignment can be specified:

#include <stdlib.h>
void *aligned_alloc(size_t alignment, size_t size);