Messages in this thread | | | Date | Fri, 8 Mar 2019 13:53:02 -0600 | From | Josh Poimboeuf <> | Subject | Re: [PATCH 03/20] x86/uaccess: Move copy_user_handle_tail into asm |
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On Fri, Mar 08, 2019 at 08:48:35PM +0100, Peter Zijlstra wrote: > On Fri, Mar 08, 2019 at 12:53:21PM -0600, Josh Poimboeuf wrote: > > On Thu, Mar 07, 2019 at 12:45:14PM +0100, Peter Zijlstra wrote: > > > /* > > > + * Try to copy last bytes and clear the rest if needed. > > > + * Since protection fault in copy_from/to_user is not a normal situation, > > > + * it is not necessary to optimize tail handling. > > > + * > > > + * Input: > > > + * rdi destination > > > + * rsi source > > > + * rdx count > > > + * > > > + * Output: > > > + * eax uncopied bytes or 0 if successful. > > > + */ > > > +ALIGN; > > > +copy_user_handle_tail: > > > + movl %edx,%ecx > > > +1: rep movsb > > > +2: mov %ecx,%eax > > > + ASM_CLAC > > > + ret > > > + > > > + _ASM_EXTABLE_UA(1b, 2b) > > > +ENDPROC(copy_user_handle_tail) > > > > This is an unstructured piece of code rather than a callable function, > > END would probably be more appropriate. Or maybe it should just be a > > local label (.Lcopy_user_handle_tail) because I don't think the > > alignment and ELF symbol size are even needed. > > ENDPROC makes it STT_FUNC and gets us stricter AC tests.
How so? I would have thought the opposite. Doesn't objtool only follow a jump if its destination is to a non-function? Otherwise it's considered a sibling call.
-- Josh
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