[Bug libc/31492] ARM ldp instruction trigger bus error when kernel open option CONFIG_IO_STRICT_DEVMEM

["luofengwc at qq dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=31492

--- Comment #3 from luofeng14 <luofengwc at qq dot com> ---
(In reply to Florian Weimer from comment #2)
> You use the x0 and x1 registers, but you don't tell the compiler about it.
> Anything may happen as a result.

there may be some misunderstandings about the problem, actually, i encountered
this problem

```
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>

typedef char u8;

void * func(void)
{
        off_t base = 9654697984;
        void *p;
        int fd;
        int len = 724;
        // scanf ("%d",&len);

        struct stat statbuf;
        off_t mmoffset;
        void *mmp;

        if ((fd = open("/dev/mem", O_RDONLY)) == -1)
        {
                printf("%d\n",__LINE__);
                return NULL;
        }

        if ((p = malloc(len)) == NULL)
        {
                printf("%d\n",__LINE__);
                return NULL;
        }

        if (fstat(fd, &statbuf) == -1)
        {
                printf("%d\n",__LINE__);
                return NULL;
        }


    mmoffset = base % sysconf(_SC_PAGESIZE);
        mmp = mmap(NULL, mmoffset + len, PROT_READ, MAP_SHARED, fd, base -
mmoffset);
        if (mmp == MAP_FAILED)
                return 0;
        memcpy(p, (char *)mmp + mmoffset, len);

        if (munmap(mmp, mmoffset + len) == -1)
        {
                return NULL;
        }

  return p;
}
int main() {
  if(!func())
    return -1;
  return 0;
}

```
in above code, the ldp command is also used in memcpy. when use memcpy to copy
/dev/mem data, alos has bus error;

using inline assembly is to simplify the problem

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