Re: [uml-devel] Re: [patch 1/1] uml: fix lvalue for gcc4

[Blaisorblade]

On Saturday 09 July 2005 13:07, Russell King wrote:
> On Sat, Jul 09, 2005 at 01:01:33PM +0200, blaisorblade@xxxxxxxx wrote:
> > diff -puN arch/um/sys-x86_64/signal.c~uml-fix-for-gcc4-lvalue
> > arch/um/sys-x86_64/signal.c ---
> > linux-2.6.git/arch/um/sys-x86_64/signal.c~uml-fix-for-gcc4-lvalue	2005-07
> >-09 13:01:03.000000000 +0200 +++
> > linux-2.6.git-paolo/arch/um/sys-x86_64/signal.c	2005-07-09
> > 13:01:03.000000000 +0200 @@ -168,7 +168,7 @@ int
> > setup_signal_stack_si(unsigned long
> >
> >  	frame = (struct rt_sigframe __user *)
> >  		round_down(stack_top - sizeof(struct rt_sigframe), 16) - 8;
> > -	((unsigned char *) frame) -= 128;
> > +	frame -= 128 / sizeof(frame);
>
> Are you sure these two are identical?
SOOOOOOOOORRY, I've become crazy, I meant sizeof(*frame)... thanks for 
noticing.

> The above code fragment looks suspicious anyway, particularly:
>
>  	frame = (struct rt_sigframe __user *)
>  		round_down(stack_top - sizeof(struct rt_sigframe), 16) - 8;
>
> which will put the frame at 8 * sizeof(struct rt_sigframe) below
> the point which round_down() would return (which would be 1 struct
> rt_sigframe below stack_top, rounded down).

You're completely right.

The code is copied from arch/x86_64/kernel/signal.c:setup_rt_frame(), so it 
should make some sense; but in the source, the cast is to (void*).

Surely Jeff, seeing that the result is assigned to a struct rt_sigframe 
__user, "fixed" it. The line I'm patching is new from Jeff, and I don't know 
what's about (I just remember that 

Also, the below access_ok() called on fp (which is still NULL) is surely 
completely wrong, though it won't fail (after all, NULL is under TASK_SIZE. 
right?).

On x86_64 the code is always used from arch/um/kernel/signal_kern.c, since 
CONFIG_whatever is not enabled.
-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade


	

	
		
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