linux-kernel - Re: [PATCH 01/32] perf tools powerpc: Cache the DWARF debug info

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Date:	Wed, 29 Oct 2014 15:39:46 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
	Anton Blanchard <anton@....ibm.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH 01/32] perf tools powerpc: Cache the DWARF debug info

Hi Arnaldo and Sukadev,

On Tue, 28 Oct 2014 11:31:55 -0200, Arnaldo Carvalho de Melo wrote:
> From: Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
> @@ -156,15 +156,27 @@ static int check_return_addr(const char *exec_file, Dwarf_Addr pc)
>  	Dwarf_Addr	end = pc;
>  	bool		signalp;
>  
> -	dwfl = dwfl_begin(&offline_callbacks);
> -	if (!dwfl) {
> -		pr_debug("dwfl_begin() failed: %s\n", dwarf_errmsg(-1));
> -		return -1;
> -	}
> +	dwfl = dso->dwfl;
>  
> -	if (dwfl_report_offline(dwfl, "",  exec_file, -1) == NULL) {
> -		pr_debug("dwfl_report_offline() failed %s\n", dwarf_errmsg(-1));
> -		goto out;
> +	if (!dwfl) {
> +		dwfl = dwfl_begin(&offline_callbacks);
> +		if (!dwfl) {
> +			pr_debug("dwfl_begin() failed: %s\n", dwarf_errmsg(-1));
> +			return -1;
> +		}
> +
> +		if (dwfl_report_offline(dwfl, "", dso->long_name, -1) == NULL) {
> +			pr_debug("dwfl_report_offline() failed %s\n",
> +						dwarf_errmsg(-1));
> +			/*
> +			 * We normally cache the DWARF debug info and never
> +			 * call dwfl_end(). But to prevent fd leak, free in
> +			 * case of error.
> +			 */

Well, it can be freed when dso__delete() called at least. :)


> +			dwfl_end(dwfl);
> +			goto out;
> +		}
> +		dso->dwfl = dwfl;
>  	}
>  
>  	mod = dwfl_addrmodule(dwfl, pc);

I don't know how dwfl_report_offline() can make it to find out a mod
from pc as it's an (loaded) virtual address.  Maybe I miss something or
is your dso's are prelinked?

Thanks,
Namhyung


> @@ -194,7 +206,6 @@ static int check_return_addr(const char *exec_file, Dwarf_Addr pc)
>  	rc = check_return_reg(ra_regno, frame);
>  
>  out:
> -	dwfl_end(dwfl);
>  	return rc;
>  }
>  
> @@ -246,7 +257,7 @@ int arch_skip_callchain_idx(struct machine *machine, struct thread *thread,
>  		return skip_slot;
>  	}
>  
> -	rc = check_return_addr(dso->long_name, ip);
> +	rc = check_return_addr(dso, ip);
>  
>  	pr_debug("DSO %s, nr %" PRIx64 ", ip 0x%" PRIx64 "rc %d\n",
>  				dso->long_name, chain->nr, ip, rc);
> diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
> index acb651acc7fd..3c9b391493f9 100644
> --- a/tools/perf/util/dso.h
> +++ b/tools/perf/util/dso.h
> @@ -127,6 +127,7 @@ struct dso {
>  	const char	 *long_name;
>  	u16		 long_name_len;
>  	u16		 short_name_len;
> +	void		*dwfl;			/* DWARF debug info */
>  
>  	/* dso data file */
>  	struct {
--
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