linux-kernel - Re: [PATCH v3 02/35] compiler-capability-analysis: Add infrastructure for Clang's capability analysis

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Message-ID: <20250918121416.19a8041e@gandalf.local.home>
Date: Thu, 18 Sep 2025 12:14:16 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Bart Van Assche <bvanassche@....org>
Cc: Ian Rogers <irogers@...gle.com>, Marco Elver <elver@...gle.com>, Peter
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Subject: Re: [PATCH v3 02/35] compiler-capability-analysis: Add
 infrastructure for Clang's capability analysis

On Thu, 18 Sep 2025 09:03:17 -0700
Bart Van Assche <bvanassche@....org> wrote:

> On 9/18/25 8:58 AM, Ian Rogers wrote:
> > On Thu, Sep 18, 2025 at 7:05 AM Marco Elver <elver@...gle.com> wrote:  
> >> +config WARN_CAPABILITY_ANALYSIS
> >> +       bool "Compiler capability-analysis warnings"
> >> +       depends on CC_IS_CLANG && CLANG_VERSION >= 220000
> >> +       # Branch profiling re-defines "if", which messes with the compiler's
> >> +       # ability to analyze __cond_acquires(..), resulting in false positives.
> >> +       depends on !TRACE_BRANCH_PROFILING  
> > 
> > Err, wow! What and huh, and why? Crikes. I'm amazed you found such an
> > option exists. I must be very naive to have never heard of it and now
> > I wonder if it is needed and load bearing?  
> 
> (+Steven)
> 
> This is an old option. I think this commit introduced it:
> 
> commit 52f232cb720a7babb752849cbc2cab2d24021209
> Author: Steven Rostedt <rostedt@...dmis.org>
> Date:   Wed Nov 12 00:14:40 2008 -0500
> 
>      tracing: likely/unlikely branch annotation tracer
> 

I still use it every year (enable it during December for a few weeks on my
workstation and server) and post the results publicly. When I get time, I
try to fix (add / remove) likely/unlikely statements. Unfortunately, I
haven't had time to look deeper at them.

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

This year I missed December and ended up running it in January instead.

-- Steve