linux-kernel - Re: [PATCH v11 14/14] unwind_user/x86: Enable compat mode frame pointer unwinding on x86

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Message-ID: <20250627100113.7f9ee77b@gandalf.local.home>
Date: Fri, 27 Jun 2025 10:01:13 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Ingo Molnar <mingo@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 bpf@...r.kernel.org, x86@...nel.org, Masami Hiramatsu
 <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Josh Poimboeuf <jpoimboe@...nel.org>, Peter Zijlstra
 <peterz@...radead.org>, Jiri Olsa <jolsa@...nel.org>, Namhyung Kim
 <namhyung@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Andrii
 Nakryiko <andrii@...nel.org>, Indu Bhagat <indu.bhagat@...cle.com>, "Jose
 E. Marchesi" <jemarch@....org>, Beau Belgrave <beaub@...ux.microsoft.com>,
 Jens Remus <jremus@...ux.ibm.com>, Linus Torvalds
 <torvalds@...ux-foundation.org>, Andrew Morton <akpm@...ux-foundation.org>,
 Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH v11 14/14] unwind_user/x86: Enable compat mode frame
 pointer unwinding on x86

On Thu, 26 Jun 2025 08:12:20 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> 
> 
> >   
> > > +/*
> > > + * If an architecture needs to initialize the state for a specific
> > > + * reason, for example, it may need to do something different
> > > + * in compat mode, it can define arch_unwind_user_init to a
> > > + * function that will perform this initialization.    
> > 
> > Please use 'func()' when referring to functions in comments.  
> 
> You mean to use "arch_unwind_user_init()"?
> 
> >   
> > > +/*
> > > + * If an architecture requires some more updates to the state between
> > > + * stack frames, it can define arch_unwind_user_next to a function
> > > + * that will update the state between reading stack frames during
> > > + * the user space stack walk.    
> > 
> > Ditto.  
> 
> And this to have arch_unwind_user_next()?

I went to go update these than realized that the are not functions. As the
comment says, "it can define arch_unwind_user_next", that means it has to be:

  #define arch_unwind_user_next arch_unwind_user_next

That's not a function. It's just setting a macro named arch_unwind_user_next to
be arch_unwind_user_next. I think adding "()" to the end of that will be
confusing. I could update it to say:

  ... it can define a macro named arch_unwind_user_next with the name of the
  function that will update ...

Would that work?

I may even change the x86 code to be:

#define arch_unwind_user_next x86_unwind_user_next

As the function name doesn't have to be the same as the macro.

-- Steve