linux-kernel - Re: [RFD] perf syscall error handling

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Date:	Mon, 10 Nov 2014 07:14:19 -0700
From:	David Ahern <dsahern@...il.com>
To:	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Vince Weaver <vince@...ter.net>,
	Stephane Eranian <eranian@...gle.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFD] perf syscall error handling

On 11/10/14, 5:24 AM, Ingo Molnar wrote:
> Programmatic use in user-spaec is very simple - go with my
> initial example, tooling can either just display the error string
> and bail out, or do:
>
>    if (unlikely(error)) {
> 	if (!strcmp(attr->error_str, "x86/bts: BTS not supported by this CPU architecture")) {
> 		fprintf(stderr, "x86/BTS: No hardware support falling back to branch sampling\n");
> 		activate_x86_bts_fallback_code();
> 		goto out;
> 	}

That makes the exact string content part of the ABI. As I recall ftrace 
had a problem with format strings changing and tooling then limiting the 
ability to change it.

David
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