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c++caixsegmentation-faultxlc

sigsegv occured when posix_memalign immediately after free in some devices and compile option in AIX

I was assigned to a pointer and it was free immediately, but sigsegv occurs depending on some devices and xlc options.

xlC_r -o cc.o c.c -lhm has sigsegv occurred, but xlC_r -o cc.o c.c works.

( lhm option is linking libhm.a libhu.a. )
( malloc and free works. Only posix_memalign and free sigsegv occurred. )

Source code: 

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

int main()
{
    void * sPtr = NULL;

    size_t sAlign = 8388608;
    size_t sSize = 8388648;
    int sRet = 0;

    sRet = posix_memalign(&sPtr, sAlign, sSize);
    printf( "after malloc : %p return : %d\n", sPtr, sRet );
    free(sPtr);

    printf( "after free\n" );
    return 0;
}

It works:

aix7.1 tl3 IBM XL C/C++ for AIX, V12.1 (5765-J02, 5725-C72) Version: 12.01.0000.0000
aix6.1 tl9 IBM XL C/C++ for AIX, V10.1 Version: 10.01.0000.0008

Result is:

after malloc : 22000000 return : 0
after free

but

aix6.1 tl3 IBM XL C/C++ for AIX, V10.1 Version: 10.01.0000.0008
aix5.3 tl9 IBM XL C/C++ for AIX, V10.1 Version: 10.01.0000.0000
aix5.3 tl1 C for AIX version 6.0.0.0 Version: 10.01.0000.0000

Result is

after malloc : 22000000 return : 0
Segmentation fault (core dumped)

% dbx cc.o core
Type 'help' for help.
[using memory image in core]
reading symbolic information ...

Segmentation fault in _ufree at 0xd3c0fcc4 ($t1)
0xd3c0fcc4 (_ufree+0x44) 80be0000         lwz   r5,0x0(r30)
(dbx) where
_ufree(??) at 0xd3c0fcc4
cbase.free(??) at 0xd2b7c048
main(), line 16 in "c.c"

I have not solved this problem although I've been trying for over a week. I searched for a bug report from AIX, but I couldn't find one.

It is not possible to delete both posix_memalign and lhm option.
Do you know a workaround or how to solve it?

Solution

  • libhm and libhmd are debug memory management libraries. They detect errors by keeping extra information after malloc and then checking before free that the block was not previously freed and that it was allocated via malloc. These libraries don't handle posix_memalign and don't keep extra information for it. So when you call free after posix_memalign, they think you're trying to free memory that was not properly allocated. That said, I don't recall that causing a segmentation fault, but a false positive error message. (I'm more used to libhmd than libhm.)

    These libraries are no longer maintained. See for example the XLF compiler manual page for them. The official recommendation is to use AIX's native debug malloc tool instead.