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Date: Mon, 2 May 2022 09:46:33 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Sami Tolvanen <samitolvanen@...gle.com> Cc: LKML <linux-kernel@...r.kernel.org>, Kees Cook <keescook@...omium.org>, Josh Poimboeuf <jpoimboe@...hat.com>, X86 ML <x86@...nel.org>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>, Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, Joao Moreira <joao@...rdrivepizza.com>, Sedat Dilek <sedat.dilek@...il.com>, Steven Rostedt <rostedt@...dmis.org>, linux-hardening@...r.kernel.org, linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>, llvm@...ts.linux.dev Subject: Re: [RFC PATCH 14/21] treewide: static_call: Pass call arguments to the macro On Fri, Apr 29, 2022 at 05:49:21PM -0700, Sami Tolvanen wrote: > On Fri, Apr 29, 2022 at 4:21 PM Peter Zijlstra <peterz@...radead.org> wrote: > > Can you explain why this is needed? I don't think there are any indirect > > calls to get confused about. That is, if you have STATIC_CALL_INLINE > > then the compiler should be emitting direct calls to the trampoline. > > Clang emits an indirect call for ({ &f; })(), which is optimized into > a direct call when possible. Come to think of it, the recent > InstCombine change to the compiler patch should solve this issue. Let > me double check, I'd be more than happy to drop these two patches. Oooh, but this must not require any magic. That is, we have a *ton* of code that relies on constant propagation of function pointers to not emit indirect calls. Please make sure that 'just-works'. Look at all the __always_inline functions in rbtree*.h for instance, some like latch and augment rely on quite complicated const propagation for the actual function pointer is in a const struct. I've verified all that actually generates direct calls when we did that code (on GCC, clang wasn't really a thing back then).
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