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

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Date:   Mon, 8 Feb 2021 09:33:00 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     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, Feb 08, 2021 at 10:02:06AM -0500, Steven Rostedt wrote:
> On Sun, 7 Feb 2021 16:45:40 -0600
> Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> 
> > > I do suspect involved people should start thinking about how they want
> > > to deal with functions starting with
> > > 
> > >         endbr64
> > >         call __fentry__
> > > 
> > > instead of the call being at the very top of the function.  
> > 
> > FWIW, objtool's already fine with it (otherwise we would have discovered
> > the need to disable fcf-protection much sooner).
> 
> And this doesn't really affect tracing (note, another user that might be
> affected is live kernel patching).

Good point, livepatch is indeed affected.  Is there a better way to get
the "call __fentry__" address for a given function?


/*
 * 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

-- 
Josh