Messages in this thread | | | Date | Sat, 11 Nov 2000 22:18:46 -0500 (EST) | From | Alexander Viro <> | Subject | Re: [PATCH] show_task() and thread_saved_pc() fix for x86 |
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On Sat, 11 Nov 2000, Linus Torvalds wrote:
> On Fri, 10 Nov 2000, Alexander Viro wrote: > > diff -urN rc11-2/include/asm-i386/processor.h rc11-2-show_task/include/asm-i386/processor.h > > --- rc11-2/include/asm-i386/processor.h Fri Nov 10 09:14:04 2000 > > +++ rc11-2-show_task/include/asm-i386/processor.h Fri Nov 10 16:08:15 2000 > > @@ -412,7 +412,7 @@ > > */ > > extern inline unsigned long thread_saved_pc(struct thread_struct *t) > > { > > - return ((unsigned long *)t->esp)[3]; > > + return ((unsigned long **)t->esp)[0][1]; > > } > > The above needs to get verified: it should be something like > > unsigned long *ebp = *((unsigned long **)t->esp); > > if ((void *) ebp < (void *) t) > return 0; > if ((void *) ebp >= (void *) t + 2*PAGE_SIZE) > return 0; > if (3 & (unsigned long)ebp) > return 0; > return *ebp; > > because otherwise I guarantee that we'll eventually have a bug with a > invalid pointer reference in the debugging code and that would be bad.
I would probably turn it into unsigned long *ebp = *((unsigned long **)t->esp);
/* Bits 0,1 and 13..31 must be shared with the stack base */ if (((unsigned long)ebp ^ (unsigned long)t) & ~(2*PAGE_SIZE-4)) return 0;
return *ebp;
Comments? Alternative variant: just let schedule() store its return address in the task_struct. Yeah, it's couple of tacts per schedule(). And much saner code, without second-guessing the compiler. OTOH, the value is used only by Alt-SysRq-T, so... Hell knows. Cheers, Al
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