Can any one solve this Problem...!!! Post: 83484

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Top Forums Programming Can any one solve this Problem...!!! Post 83484 by Perderabo on Thursday 15th of September 2005 09:51:04 AM

09-15-2005

Administrator Emeritus

A solution involving portable C eludes me! I naturally rejected the idea of having change() locate its return address on the stack and alter it to step over the i=10 statement. The precise location of the return address and even whether to increment it or decrement it and certainly by how much can vary from system to system. There is really no guarantee that the return address will be stored on the stack or even that there is a stack. I admit that I don't know of any currently marketed unix systems without a stack or that move the PC backwards. But I also don't know of any standard prohibiting them. These days we are in transistion from 32 bit to 64 bit architectures. Most versions of unix currently support executables in either architecture. So the change() function would need to detect the length of the return address as well.

But the other problem that I see with this involves agressive optimization. There is no indication that i is accessible to change() or is otherwise aliased or volatile. So there is no reason that the compiler writer could not legally choose to emit code that operates like...
i=10;
change();
printf("%d",i);
Whether or not that would happen would probably depend on the optimization level selected and the compiler used, and whether or not the resulting executable is intended to interact with a symbolic debugger.

So if you have a portable solution, I would love to see it!

Perderabo

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LEARN ABOUT LINUX

pthread_attr_setstackaddr

PTHREAD_ATTR_SETSTACKADDR(3)				     Linux Programmer's Manual				      PTHREAD_ATTR_SETSTACKADDR(3)

NAME

       pthread_attr_setstackaddr, pthread_attr_getstackaddr - set/get stack address attribute in thread attributes object

SYNOPSIS

       #include <pthread.h>

       int pthread_attr_setstackaddr(pthread_attr_t *attr, void *stackaddr);
       int pthread_attr_getstackaddr(pthread_attr_t *attr, void **stackaddr);

       Compile and link with -pthread.

DESCRIPTION

       These functions are obsolete: do not use them.  Use pthread_attr_setstack(3) and pthread_attr_getstack(3) instead.

       The  pthread_attr_setstackaddr() function sets the stack address attribute of the thread attributes object referred to by attr to the value
       specified in stackaddr.	This attribute specifies the location of the stack that should be used by a  thread  that  is  created	using  the
       thread attributes object attr.

       stackaddr should point to a buffer of at least PTHREAD_STACK_MIN bytes that was allocated by the caller.  The pages of the allocated buffer
       should be both readable and writable.

       The pthread_attr_getstackaddr() function returns the stack address attribute of the thread attributes object referred to  by  attr  in  the
       buffer pointed to by stackaddr.

RETURN VALUE

       On success, these functions return 0; on error, they return a nonzero error number.

ERRORS

       No errors are defined (but applications should nevertheless handle a possible error return).

VERSIONS

       These functions are provided by glibc since version 2.1.

CONFORMING TO

       POSIX.1-2001 specifies these functions but marks them as obsolete.  POSIX.1-2008 removes the specification of these functions.

NOTES

       Do  not use these functions!  They cannot be portably used, since they provide no way of specifying the direction of growth or the range of
       the stack.  For example, on architectures with a stack that grows downwards, stackaddr specifies the next address past the highest  address
       of  the	allocated  stack  area.   However, on architectures with a stack that grows upwards, stackaddr specifies the lowest address in the
       allocated stack area.  By contrast, the stackaddr used by pthread_attr_setstack(3) and pthread_attr_getstack(3), is always a pointer to the
       lowest address in the allocated stack area (and the stacksize argument specifies the range of the stack).

SEE ALSO

       pthread_attr_init(3), pthread_attr_setstack(3), pthread_attr_setstacksize(3), pthread_create(3), pthreads(7)

COLOPHON

       This  page is part of release 3.27 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2008-10-24					      PTHREAD_ATTR_SETSTACKADDR(3)