Re: [PATCH][2.6-mm] Fix 4G/4G X11/vm86 oops

[Zwane Mwaikambo <zwane@arm.linux.org.uk>]

On Tue, 18 Nov 2003, Linus Torvalds wrote:

> Ok. Much more readable.
> 
> And there is something very suspicious there.
> 
> The code with and without the printk() looks _identical_ apart from some 
> trivial label renumbering, and the added
> 
> 	pushl   $.LC6
> 	call    printk
> 	.. asm ..
> 	popl %esi
> 
> which all looks fine (esi is dead at that point, so the compiler is just
> using a "popl" as a shorter form of "addl $4,%esp").
> 
> Btw, you seem to compile with debugging, which makes the assembly 
> language pretty much unreadable and accounts for most of the 
> differences: the line numbers change. If you compile a kernel where the 
> line numbers don't change (by commenting _out_ the printk rather than 
> removing the whole line), your diff would be more readable.

Aha! Thanks for mentioning that, noted.

> Anyway, there are _zero_ differences.
> 
> Just for fun, try this: move the "printk()" to _below_ the "asm"  
> statement. It will never actually get executed, but if it's an issue of
> some subtle code or data placement things (cache lines etc), maybe that
> also hides the oops, since all the same code and data will be generated, 
> just not run...

Ok i just tried that and it still fails. Matt Mackall suggested i also try 
writing a minimal printk which has the same effect.
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