Re: PATCH: Fix 20000724-1.c

[Richard Henderson <rth at redhat dot com>]

On Mon, Apr 30, 2001 at 07:59:41AM -0700, Mark Mitchell wrote:
> In looking at it carefully, I think the extended asm is bogus.  In
> particular, we have:
> 
>   !   asm volatile("call ___checkme" : : "c" (x) : "memory");
> 
> where `__checkme' is a function which fiddles around with the stack.
> The asm doesn't clobber the stack pointer, which is wrong; GCC has no
> way to know that this instruction messes with that register.

This analysis is incorrect, as far as I can tell.  The asm 
does not need to describe the change in the stack pointer
because it should have the same value before and after.

Yes, the call pushes a return address, but the ret in checkme
removes it.

The actual flaw is that we've lost track of the fact that 
there is an outstanding reference to a stack address in a 
register, and we decide that we can deallocate the stack
frame before that reference is used.


r~