Messages in this thread | | | Date | Wed, 20 May 2009 13:56:24 -0700 | From | "H. Peter Anvin" <> | Subject | Re: Q: put_user_try & co (Was: [PATCH 1/5] Split wait_noreap_copyout()) |
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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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