linux-kernel - Re: [RFC PATCH 7/8] perf probe powerpc: Use DWARF info only if necessary

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Message-ID: <1418206640.9279.10.camel@ellerman.id.au>
Date:	Wed, 10 Dec 2014 21:17:20 +1100
From:	Michael Ellerman <mpe@...erman.id.au>
To:	"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
Cc:	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	acme@...nel.org, ananth@...ibm.com
Subject: Re: [RFC PATCH 7/8] perf probe powerpc: Use DWARF info only if
 necessary

On Tue, 2014-12-09 at 23:04 +0530, Naveen N. Rao wrote:
> Use symbol table lookups by default if DWARF is not necessary, since
> powerpc ABIv2 encodes local entry points in the symbol table and the
> function entry address in DWARF may not be appropriate for kprobes,
> as described here:
> https://sourceware.org/bugzilla/show_bug.cgi?id=17638

Needs a better changelog.

> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index 174c22e..adcdbd2 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -2382,6 +2382,14 @@ static int convert_to_probe_trace_events(struct perf_probe_event *pev,
>  		}
>  	}
>  
> +#if defined(__powerpc64__) && defined(_CALL_ELF) && _CALL_ELF == 2
> +	if (!perf_probe_event_need_dwarf(pev)) {
> +		ret = find_probe_trace_events_from_map(pev, tevs, max_tevs, target);
> +		if (ret > 0)
> +			return ret;	/* Found in symbol table */
> +	}
> +#endif

And should be in an arch helper, not a big powerpc wart dropped in the middle
of the generic code.

cheers


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