On Thu, 2018-01-11 at 15:32 +0100, Peter Zijlstra wrote: > On Thu, Jan 11, 2018 at 02:28:32PM +0000, David Woodhouse wrote: > > > > On Thu, 2018-01-11 at 08:20 -0600, Josh Poimboeuf wrote: > > > > > > > > > This seems weird. I liked v1 a lot better. What's the problem with > > > patching in the whole thing? > > > > > > Also, if you go back to v1, it should be an easy objtool fix, just add > > > ANNOTATE_NOSPEC_ALTERNATIVE in front of it. > > The objection was that I was patching in a fairly long set of > > instructions. I confess I don't actually know why that's a problem, > > You get a giant string of NOPs, a single jmp should be faster.
How about this one then (with ANNOTATE_NOSPEC_ALTERNATIVE):
- asm volatile (ALTERNATIVE("",
+ asm volatile (ALTERNATIVE("jmp " alt_end_marker "f",
__stringify(__FILL_RETURN_BUFFER(%0, %1,
_%=)),
X86_FEATURE_RETPOLINE)
: "=r" (dummy), ASM_CALL_CONSTRAINT : : "memory" );
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