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problem with thread stack using pthread_attr_setstackaddr()

When I set the stack base address of the child thread using the POSIX library function "pthread_attr_setstackaddr()", I am unable to access the memory contents of its parent. The data-structures that are created on the HEAP of its parent using malloc() are either getting destroyed or unaccessible when moving to the context of the child thread. These data-structures are being passed as an argument to the child thread.
Even if I make these variables global then also it is not working.
pthread_attr_setstacksize(tattr, ...);
stackbase = (void *) malloc(...);
pthread_attr_setstackaddr(tattr, stackbase);

But when I create the child thread without setting its stack base address using that pthread_attr_setstackaddr(), then it is able to access the parent's memory contents.

Why is that so ? Can anybody explain this ?

Quote:

Originally Posted by subham (Post 4105464)

You should be using pthread_attr_setstack, since pthread_attr_setstacksize and pthread_attr_setstackaddr are now deprecated.

The most likely reason for your error is because the pthread_attr_setstackaddr does not set the base of the stack, but the initial stack pointer. On an x86 architecture and many others, this is the end of the allocated stack space (which is why it is non-portable and is now deprecated).

If you set it to the start of the allocated space, the stack will grow down into other memory and cause heap corruptions. Depending on your architecture, you could have used pthread_attr_setstackaddr(tattr, stackbase+stacksize) to fix your memory corruption.

The example below illustrates a child accessing the heap of the parent, with no issues.

Code:

#include <stdlib.h>

#include <stdio.h>

#include <pthread.h>

void *threadFn(void *arg)

{

// print string

        puts((char *) arg);

}

int main()

{

// create a string on the heap

        char *arg = malloc(3);

        arg[0] = '4'; arg[1] = '2'; arg[2] = 0;

// create a stack

        pthread_attr_t attr;

        pthread_attr_init(&attr);

        pthread_attr_setstack(&attr, malloc(4096), 4096);

// start child thread

        pthread_t thread;

        pthread_create(&thread, &attr, threadFn, arg);

        pthread_attr_destroy(&attr);

        pthread_join(thread, 0);

}