Hello!
Since 2.6.10, unbacked private shared memory allocated via shmget is not
included in core dumps.
This is a simple example code demonstrating the bug:
#include <sys/shm.h>
int main(int argc, char ** argv)
{
int size = 1000;
int id = shmget(IPC_PRIVATE, size, (IPC_CREAT | 0660));
if(id < 0) return(1);
int *buffer = (int *)shmat(id, 0, 0);
int i;
for(i = 0; i < 1000; i++)
buffer[i] = i;
// now dump core
*((unsigned long *)1) = 0;
// The private shared memory is not included in the core dump,
// although it's not backed and cannot be accessed any more in any
// way.
return 0;
}
This bug was introduced in 2.6.10 by a patch to binfmt_elf.c that
resulted in:
static int maydump(struct vm_area_struct *vma)
{
/* Do not dump I/O mapped devices, shared memory, or special mappings */
if (vma->vm_flags & (VM_IO | VM_SHARED | VM_RESERVED))
return 0;
...
(See the thread at
http://www.ussg.iu.edu/hypermail/linux/kernel/0410.2/1890.html)
Excluding all pages with VM_SHARED set is also excluding the unbacked
private mapping and should be replaced by a more specific criterion.
Bye
Jochen
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