linux-kernel - Re: [PATCH v6 14/17] static

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Message-ID: <20200711050618.GW597537@hirez.programming.kicks-ass.net>
Date:   Sat, 11 Jul 2020 07:06:18 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, mhiramat@...nel.org,
        bristot@...hat.com, jbaron@...mai.com,
        torvalds@...ux-foundation.org, tglx@...utronix.de,
        mingo@...nel.org, namit@...are.com, hpa@...or.com, luto@...nel.org,
        ard.biesheuvel@...aro.org, jpoimboe@...hat.com,
        pbonzini@...hat.com, mathieu.desnoyers@...icios.com,
        linux@...musvillemoes.dk
Subject: Re: [PATCH v6 14/17] static_call: Handle tail-calls

On Fri, Jul 10, 2020 at 08:23:19PM -0400, Steven Rostedt wrote:
> On Fri, 10 Jul 2020 15:38:45 +0200
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > GCC can turn our static_call(name)(args...) into a tail call, in which
> > case we get a JMP.d32 into the trampoline (which then does a further
> > tail-call).
> > 
> > Teach objtool to recognise and mark these in .static_call_sites and
> > adjust the code patching to deal with this.
> > 
> 
> Hmm, were you able to trigger crashes before this patch?

No, just a bunch of tail-calls that didn't get patched and would still
point to the trampoline.