Ok,
On X86, MIPS
#./tc1
mmap: addr 0x20000000
#
#

On ARM (2.6.35.11 ~ 3.0.2)
#tc1
map: addr 0x20000000
tc1: unhandled page fault (7) at 0x20001000, code 0x817
Bus error (core dumped)
#
#
Debug Information
Pid: 179, comm:                  tc1
CPU: 0    Not tainted  (2.6.35.11 #1)
PC is at 0x400da410
LR is at 0x8858
pc : [<400da410>]    lr : [<00008858>]    psr: 20000010
sp : bed84814  ip : 20001080  fp : 00000000
r10: 40025000  r9 : 00000000  r8 : 00000000
r7 : 20000000  r6 : 20001000  r5 : 00000000  r4 : 0000ef80
r3 : 00000000  r2 : 20010000  r1 : 00000000  r0 : 20000000
Flags: nzCv  IRQs on  FIQs on  Mode USER_32  ISA ARM  Segment user

Process Memory map
00008000-00009000 r-xp 00000000 08:01 153 /usb/sda1/tc1
00010000-00011000 rw-p 00000000 08:01 153 /usb/sda1/tc1
00011000-00032000 rw-p 00011000 08:01 153
20000000-20010000 rw-s 00000000 00:0d 249 /dev/shm/shmem_1234
40000000-4001d000 r-xp 00000000 8b:06 163 /lib/ld-2.11.1.so
4001d000-40021000 rw-p 4001d000 8b:06 163
40024000-40025000 r--p 0001c000 8b:06 163 /lib/ld-2.11.1.so
40025000-40026000 rw-p 0001d000 8b:06 163 /lib/ld-2.11.1.so
40026000-4003b000 r-xp 00000000 8b:06 171 /lib/libpthread-2.11.1.so
4003b000-40042000 ---p 00015000 8b:06 171 /lib/libpthread-2.11.1.so
40042000-40043000 r--p 00014000 8b:06 171 /lib/libpthread-2.11.1.so
40043000-40044000 rw-p 00015000 8b:06 171 /lib/libpthread-2.11.1.so
40044000-40046000 rw-p 40044000 8b:06 171
40046000-4004c000 r-xp 00000000 8b:06 161 /lib/librt-2.11.1.so
4004c000-40053000 ---p 00006000 8b:06 161 /lib/librt-2.11.1.so
40053000-40054000 r--p 00005000 8b:06 161 /lib/librt-2.11.1.so
40054000-40055000 rw-p 00006000 8b:06 161 /lib/librt-2.11.1.so
40055000-4005f000 r-xp 00000000 8b:06 165 /lib/libgcc_s.so.1
4005f000-40067000 ---p 0000a000 8b:06 165 /lib/libgcc_s.so.1
40067000-40068000 rw-p 0000a000 8b:06 165 /lib/libgcc_s.so.1
40068000-40185000 r-xp 00000000 8b:06 174 /lib/libc-2.11.1.so
40185000-4018d000 ---p 0011d000 8b:06 174 /lib/libc-2.11.1.so
4018d000-4018f000 r--p 0011d000 8b:06 174 /lib/libc-2.11.1.so
4018f000-40190000 rw-p 0011f000 8b:06 174 /lib/libc-2.11.1.so
40190000-40193000 rw-p 40190000 8b:06 174
bed63000-bed85000 rw-p befde000 8b:06 174

We wish to know why the same application crashes on ARM ?
On Wed, Nov 16, 2011 at 1:57 PM, Russell King - ARM Linux
[off-list ref] wrote:

On Wed, Nov 16, 2011 at 11:05:49AM +0530, naveen yadav wrote:

quoted

Hi All,

I am running below Test program on ARM cortex a9/a8 on kernel version
2.6.35.14 as well as on 3.0.

Please find the test case where:

1. Create shared memory object using shm_open(If we use normal open
then no problem only problem with shm_open)

2. ftruncate to given size

3. memory map the shared object to given memory address ( I haved
tested without MAP_SHARED, MAP_FIXED as well, problem exist)

4. Memset the shared memory (got page fault when accessing the second page)




Observation: Only observed in ARM ( i.e not present in MIPS and X86)

Yes, so, what happens?

quoted

#undef NDEBUG
#define _GNU_SOURCE
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <errno.h>
#include <pthread.h>
#include <string.h>
#include <signal.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/mman.h>

enum {
?SHM_INIT,
?SHM_GET
?};

enum {
?PARENT,
?CHILD
?};

#define FIXED_MMAP_ADDR 0x20000000
#define MMAP_SIZE ? ? 0x10000

static int shmid;
static char shm_name[100];
static int sleep_period = 100000;
void * shmem_init(int flag)
{
? ? ? int start = FIXED_MMAP_ADDR;
? ? ? int memory_size = MMAP_SIZE;
? ? ? int mode = 0666;
? ? ? void *addr;
? ? ? int ret;
? ? ? sprintf(shm_name, "/shmem_1234");
? ? ? shmid = shm_open (shm_name, O_RDWR | O_EXCL | O_CREAT | O_TRUNC, mode);
? ? ? if (shmid < 0) {
? ? ? ? ? ? ? if (errno == EEXIST) {
? ? ? ? ? ? ? ? ? ? ? printf ("shm_open: %s\n", strerror(errno));
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? shmid = shm_open (shm_name, O_RDWR, mode);

? ? ? ? ? ? ? } else {
? ? ? ? ? ? ? ? ? ? ? printf("failed to shm_open, err=%s\n", strerror(errno));
? ? ? ? ? ? ? ? ? ? ? return NULL;
? ? ? ? ? ? ? }
? ? ? }
? ? ? ret = fcntl (shmid, F_SETFD, FD_CLOEXEC);
? ? ? if (ret < 0) {
? ? ? ? ? ? ? printf("fcntl: %s\n", strerror(errno));
? ? ? ? ? ? ? return NULL;
? ? ? }
? ? ? ret = ftruncate (shmid, memory_size);
? ? ? if (ret < 0) {
? ? ? ? ? ? ? printf("ftruncate: %s\n", strerror(errno));
? ? ? ? ? ? ? return NULL;
? ? ? }
? ? ? addr = mmap ((void *)start, memory_size, PROT_READ | PROT_WRITE,
? ? ? ? ? ? ? ? ? ? ? ? ? ?MAP_SHARED | MAP_FIXED, shmid, 0);
? ? ? if (addr == MAP_FAILED) {
? ? ? ? ? ? ? printf ("mmap: %s\n", strerror(errno));
? ? ? ? ? ? ? close (shmid);
? ? ? ? ? ? ? shm_unlink (shm_name);
? ? ? ? ? ? ? return NULL;
? ? ? }

? ? ? if (flag == SHM_INIT){
? ? ? ? ? ? ? printf ("mmap: addr %p\n", addr);
? ? ? ? ? ? ? /* memset on arm creates a unhandled page fault, works fine on mips */
? ? ? ? ? ? ? memset(addr, 0, memory_size);
? ? ? }
? ? ? return (void *)addr;
}

pthread_mutex_t * shmem_mutex_init(int flag)
{
? ? ? pthread_mutex_t * pmutex = (pthread_mutex_t *)shmem_init(flag);
#if 0
? ? ? pthread_mutexattr_t attr;
? ? ? if (flag == SHM_INIT) {
? ? ? ? ? ? ? pthread_mutexattr_init (&attr);
? ? ? ? ? ? ? pthread_mutexattr_setpshared (&attr, PTHREAD_PROCESS_SHARED);
? ? ? ? ? ? ? pthread_mutexattr_setprotocol (&attr, PTHREAD_PRIO_INHERIT);
? ? ? ? ? ? ? pthread_mutexattr_setrobust_np (&attr,
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? PTHREAD_MUTEX_STALLED_NP);
? ? ? ? ? ? ? pthread_mutexattr_settype (&attr, PTHREAD_MUTEX_ERRORCHECK);
? ? ? ? ? ? ? if (pthread_mutex_init (pmutex, &attr) != 0) {
? ? ? ? ? ? ? ? ? ? ? printf("Init mutex failed, err=%s\n", strerror(errno));
? ? ? ? ? ? ? ? ? ? ? pthread_mutexattr_destroy (&attr);
? ? ? ? ? ? ? ? ? ? ? return NULL;
? ? ? ? ? ? ? }
? ? ? }
#endif
? ? ? return pmutex;
}

void long_running_task(int flag)
{
? ? ? static int counter = 0;
? ? ? if (flag == PARENT)
? ? ? ? ? ? ? usleep(5*sleep_period);
? ? ? else
? ? ? ? ? ? ? usleep(3*sleep_period);
? ? ? counter = (counter + 1) % 100;
? ? ? printf("%d: completed %d computing\n", getpid(), counter);
}

void sig_handler(int signum)
{
? ? ? close(shmid);
? ? ? shm_unlink(shm_name);
? ? ? exit(0);
}

int main(int argc, char *argv[])
{
? ? ? pthread_mutex_t *mutex_parent, *mutex_child;
// ? ?signal(SIGUSR1, sig_handler);
// ? ?if (fork()) {
? ? ? ? ? ? ? /* parent process */
? ? ? ? ? ? ? if ((mutex_parent = shmem_mutex_init(SHM_INIT)) == NULL) {
? ? ? ? ? ? ? ? ? ? ? printf("failed to get the shmem_mutex\n");
? ? ? ? ? ? ? ? ? ? ? exit(-1);
? ? ? ? ? ? ? }
#if 0
? ? ? ? ? ? ? while (1) {
? ? ? ? ? ? ? ? ? ? ? printf("%d: try to hold the lock\n", getpid());
? ? ? ? ? ? ? ? ? ? ? pthread_mutex_lock(mutex_parent);
? ? ? ? ? ? ? ? ? ? ? printf("%d: got the lock\n", getpid());
? ? ? ? ? ? ? ? ? ? ? long_running_task(PARENT);
? ? ? ? ? ? ? ? ? ? ? pthread_mutex_unlock(mutex_parent);
? ? ? ? ? ? ? ? ? ? ? printf("%d: released the lock\n", getpid());
? ? ? ? ? ? ? }
#endif
// ? ?} else {
#if 0
? ? ? ? ? ? ? /* child process */
? ? ? ? ? ? ? usleep(sleep_period);
? ? ? ? ? ? ? if ((mutex_child = shmem_mutex_init(SHM_GET)) == NULL) {
? ? ? ? ? ? ? ? ? ? ? printf("failed to get the shmem_mutex\n");
? ? ? ? ? ? ? ? ? ? ? exit(-1);
? ? ? ? ? ? ? }
? ? ? ? ? ? ? while (1) {
? ? ? ? ? ? ? ? ? ? ? printf("%d: try to hold the lock\n", getpid());
? ? ? ? ? ? ? ? ? ? ? pthread_mutex_lock(mutex_child);
? ? ? ? ? ? ? ? ? ? ? printf("%d: got the lock\n", getpid());
? ? ? ? ? ? ? ? ? ? ? long_running_task(CHILD);
? ? ? ? ? ? ? ? ? ? ? pthread_mutex_unlock(mutex_child);
? ? ? ? ? ? ? ? ? ? ? printf("%d: released the lock\n", getpid());
? ? ? ? ? ? ? }
#endif
// ? ?}
? ? ? return 0;
}