linux-kernel - Re: [RFC PATCH v2] perf/x86: make perf callchain work without CONFIG_FRAME

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Message-ID: <20190418075412.GO12232@hirez.programming.kicks-ass.net>
Date:   Thu, 18 Apr 2019 09:54:12 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kairui Song <kasong@...hat.com>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, Dave Young <dyoung@...hat.com>
Subject: Re: [RFC PATCH v2] perf/x86: make perf callchain work without
 CONFIG_FRAME_POINTER

On Wed, Apr 17, 2019 at 10:44:33PM +0800, Kairui Song wrote:
> Despite it's hacky, it seems not necessary to dump every register. And
> is there a straight way to get caller's regs in the trace point? It
> seems more trouble some. Or if we just use the regs inside the
> tracepoint, but it would need even more workaround (eg. unwind one
> frame before do anything).

Sure, and the current code doesn't fill out every reg either, but given
SAMPLE_REGS_INTR I think we should at least clear the entire regs before
passing it on, or otherwise make sure SAMPLE_REGS_INTR isn't allowed on
these events.