linux-kernel - Re: [GIT PULL] x86/urgent for v5.11-rc7

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Message-ID: <20210208111546.5e01c3fb@gandalf.local.home>
Date:   Mon, 8 Feb 2021 11:15:46 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Borislav Petkov <bp@...e.de>,
        Dave Hansen <dave.hansen@...el.com>, x86-ml <x86@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        live-patching@...r.kernel.org
Subject: Re: [GIT PULL] x86/urgent for v5.11-rc7

On Mon, 8 Feb 2021 16:47:05 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> > /*
> >  * Convert a function address into the appropriate ftrace location.
> >  *
> >  * Usually this is just the address of the function, but on some architectures
> >  * it's more complicated so allow them to provide a custom behaviour.
> >  */
> > #ifndef klp_get_ftrace_location
> > static unsigned long klp_get_ftrace_location(unsigned long faddr)
> > {
> > 	return faddr;
> > }
> > #endif  
> 
> I suppose the trivial fix is to see if it points to endbr64 and if so,
> increment the addr by the length of that.

I thought of that too. But one thing that may be possible, is to use
kallsym. I believe you can get the range of a function (start and end of
the function) from kallsyms. Then ask ftrace for the addr in that range
(there should only be one).

-- Steve