linux-kernel - Re: [tip: objtool/core] objtool: Add CONFIG_OBJTOOL

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Message-ID: <20250320131028.2fea4c73@batman.local.home>
Date: Thu, 20 Mar 2025 13:10:28 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
 linux-tip-commits@...r.kernel.org, "Peter Zijlstra (Intel)"
 <peterz@...radead.org>, x86@...nel.org
Subject: Re: [tip: objtool/core] objtool: Add CONFIG_OBJTOOL_WERROR

On Mon, 17 Mar 2025 17:05:22 -0700
Josh Poimboeuf <jpoimboe@...hat.com> wrote:


> Hm, I'm actually surprised randconfig doesn't set COMPILE_TEST.
> 
> Anyway, the warnings are valid:
> 
>   vmlinux.o: error: objtool: do_syscall_64+0x40: call to ftrace_likely_update() leaves .noinstr.text section
>   vmlinux.o: error: objtool: do_int80_emulation+0x30: call to ftrace_likely_update() leaves .noinstr.text section
>   vmlinux.o: error: objtool: do_fast_syscall_32+0x7b: call to ftrace_likely_update() leaves .noinstr.text section
>   ...
> 
> Those are triggered by CONFIG_TRACE_BRANCH_PROFILING which adds a
> function call to ftrace_likely_update() for every likely() / unlikely().
> Which obliterates the noinstr rules.
> 
> Steven, do you still want to keep that config option?

Yes, in fact I just ran it a couple of months ago:

  https://rostedt.org/branches/current/

That's the output of both the likely and unlikely output as well as the
full branch tracer. I do look at this to fix places that are incorrect.

> 
> If so, I suppose we could make OBJTOOL_WERROR depend on
> !TRACE_BRANCH_PROFILING.
> 

That, or you can disable it for files with:

  CFLAGS_<file>.o += -DDISABLE_BRANCH_PROFILING

In the Makefile.

-- Steve