linux-kernel - Re: [RFC PATCH 14/21] treewide: static_call: Pass call arguments to the macro

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Date:   Sat, 30 Apr 2022 01:21:32 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>, 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@...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 01:36:37PM -0700, Sami Tolvanen wrote:
> Include the function arguments in the static call macro to make it
> possible to add a wrapper for the call. This is needed with
> CONFIG_CFI_CLANG to disable indirect call checking for static calls
> that are patched into direct calls at runtime.
> 
> Users of static_call were updated using the following Coccinelle
> script and manually adjusted to preserve coding style:
> 
>   @@
>   expression name;
>   expression list args;
>   identifier static_call =~ "^static_call(_mod|_cond)?$";
>   @@
> 
>   - static_call(name)(args)
>   + static_call(name, args)

Urgh, sadness.. I worked so hard to get away from that terrible syntax.

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.

At no point will there be an indirect call.