Re: Q: put_user_try & co (Was: [PATCH 1/5] Split wait_noreap_copyout())

[H. Peter Anvin]

Roland McGrath wrote:
> 
> You mean &&__efault_label here (it's a funny syntax, but that's how it is).
> &&label is a GCC extension that I'm not sure the kernel has used before.
> 
> I think it can be touchy to have an asm jump into compiled code that way.
> e.g., perhaps the compiler produced:
> 
> 	mov reg, 40(sp)
> 	mov $123, reg
> 	#APP
> 	... inside of your asm ...
> 	#NO_APP
> 	mov 40(sp), reg
> 
> or some such thing.  If you jump away from inside the asm, you won't ever
> do "mov 40(sp), reg".  But the compiler might think that reg has its
> original value at the __efault_label: code location.
> 
> Perhaps more important than any particular compiler-confusion scenario we
> can come up with is simply that this would be an obscure corner of code
> generation in the compiler that the kernel has not evoked before.  There
> might be bugs or oddities in various compilers of various vintages, that
> we don't know about because they never came up before.
> 

Yes, it seems like a bad idea to me.

	-hpa
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