[HACKERS] mremap and bus error

[Pavel Stehule]

Hi,

I playing with mmap. I have  a problem with mremap function. It
doesn't allocate correct memory.  All others work well.

static void *
mmap_realloc(void *ptr, Size size)
{
        Size oldsize;
        void *result;
        int     i;
        char *x;

        ptr = (char *) ptr - MAXALIGN(sizeof(Size));

        oldsize = *((Size *) ptr);
        size = MAXALIGN(size) + MAXALIGN(sizeof(Size));

        ptr = mremap(ptr, oldsize,
                                    size,
                                    MREMAP_MAYMOVE);

        if (ptr == MAP_FAILED)
                ereport(ERROR,
                        (errcode(ERRCODE_OUT_OF_MEMORY),
                         errmsg("out of memory"),
                         errdetail("Failed on request of size %lu.",
                                           (unsigned long) size)));

        *((Size*) ptr) = size;
        result = (char *) ptr + MAXALIGN(sizeof(Size));

        /* check allocated memory */
        x = ptr;

        fprintf(stderr, "allocated memory %ld\n", size);
        for (i = 0; i < size; i++)
        {
                if (i > oldsize)
                {
                        *x = 0;
                }
                x++;
        }
        fprintf(stderr, "memory checked\n");

        return result;
}

log:
>>>> 1 <<<>>> 1048584
>>>> 3 <<<>>> 2097216
>>>> 3 <<<>>> 9024
allocated memory 10304
memory checked
allocated memory 11584
memory checked
allocated memory 12864

gdb

Program terminated with signal 7, Bus error.
#0  mmap_realloc (size=12864, ptr=<value optimized out>) at mmap_alloc.c:357
357                             *x = 0;
Missing separate debuginfos, use: debuginfo-install glibc-2.10.2-1.x86_64

(gdb) print x
$1 = 0x7f92055df000 ""
(gdb) print i
$2 = 12289

Can somebody help me?

Regards
Pavel Stehule

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