Commit 8737d9e0 authored by Peter Lieven's avatar Peter Lieven Committed by Kevin Wolf
Browse files

oslib-posix: add helpers for stack alloc and free 



the allocated stack will be adjusted to the minimum supported stack size
by the OS and rounded up to be a multiple of the system pagesize.
Additionally an architecture dependent guard page is added to the stack
to catch stack overflows.

Signed-off-by: default avatarPeter Lieven <pl@kamp.de>
Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
parent 74e1ae7c

include/sysemu/os-posix.h

+27 −0
Original line number Diff line number Diff line
@@ -60,4 +60,31 @@ int qemu_utimens(const char *path, const qemu_timespec *times); 


bool is_daemonized(void);



/**

 * qemu_alloc_stack:

 * @sz: pointer to a size_t holding the requested usable stack size

 *

 * Allocate memory that can be used as a stack, for instance for

 * coroutines. If the memory cannot be allocated, this function

 * will abort (like g_malloc()). This function also inserts an

 * additional guard page to catch a potential stack overflow.

 * Note that the memory required for the guard page and alignment

 * and minimal stack size restrictions will increase the value of sz.

 *

 * The allocated stack must be freed with qemu_free_stack().

 *

 * Returns: pointer to (the lowest address of) the stack memory.

 */

void *qemu_alloc_stack(size_t *sz);



/**

 * qemu_free_stack:

 * @stack: stack to free

 * @sz: size of stack in bytes

 *

 * Free a stack allocated via qemu_alloc_stack(). Note that sz must

 * be exactly the adjusted stack size returned by qemu_alloc_stack.

 */

void qemu_free_stack(void *stack, size_t sz);



#endif

util/oslib-posix.c

+42 −0
Original line number Diff line number Diff line
@@ -499,3 +499,45 @@ pid_t qemu_fork(Error **errp) 
    }

    return pid;

}



void *qemu_alloc_stack(size_t *sz)

{

    void *ptr, *guardpage;

    size_t pagesz = getpagesize();

#ifdef _SC_THREAD_STACK_MIN

    /* avoid stacks smaller than _SC_THREAD_STACK_MIN */

    long min_stack_sz = sysconf(_SC_THREAD_STACK_MIN);

    *sz = MAX(MAX(min_stack_sz, 0), *sz);

#endif

    /* adjust stack size to a multiple of the page size */

    *sz = ROUND_UP(*sz, pagesz);

    /* allocate one extra page for the guard page */

    *sz += pagesz;



    ptr = mmap(NULL, *sz, PROT_READ | PROT_WRITE,

               MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);

    if (ptr == MAP_FAILED) {

        abort();

    }



#if defined(HOST_IA64)

    /* separate register stack */

    guardpage = ptr + (((*sz - pagesz) / 2) & ~pagesz);

#elif defined(HOST_HPPA)

    /* stack grows up */

    guardpage = ptr + *sz - pagesz;

#else

    /* stack grows down */

    guardpage = ptr;

#endif

    if (mprotect(guardpage, pagesz, PROT_NONE) != 0) {

        abort();

    }



    return ptr;

}



void qemu_free_stack(void *stack, size_t sz)

{

    munmap(stack, sz);

}