linux-kernel - Re: [PATCH -tip ] [BUGFIX] perf probe: Add a workaround for GCC -mfentry

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Message-ID: <1349272435.22822.165.camel@gandalf.local.home>
Date:	Wed, 03 Oct 2012 09:53:55 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Ingo Molnar <mingo@...e.hu>, Michal Marek <mmarek@...e.cz>,
	Andi Kleen <andi@...stfloor.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Paul Mackerras <paulus@...ba.org>, systemtap@...rceware.org,
	yrl.pp-manager.tt@...achi.com
Subject: Re: [PATCH -tip ] [BUGFIX] perf probe: Add a workaround for GCC
 -mfentry

On Wed, 2012-10-03 at 21:17 +0900, Masami Hiramatsu wrote:

> Here are examples:
> -----
>  <1><9a58>: Abbrev Number: 86 (DW_TAG_subprogram)
>     <9a59>   DW_AT_external    : 1
>     <9a59>   DW_AT_name        : (indirect string, offset: 0xd82): unregister_di
> e_notifier
>     <9a5d>   DW_AT_decl_file   : 1
>     <9a5e>   DW_AT_decl_line   : 551
>     <9a60>   DW_AT_prototyped  : 1
>     <9a60>   DW_AT_type        : <0x7c>
>     <9a64>   DW_AT_low_pc      : 0x740
>     <9a6c>   DW_AT_high_pc     : 0x75a
>     <9a74>   DW_AT_frame_base  : 1 byte block: 9c       (DW_OP_call_frame_cfa)
>     <9a76>   DW_AT_GNU_all_call_sites: 1
>     <9a76>   DW_AT_sibling     : <0x9aac>
>  <2><9a7a>: Abbrev Number: 87 (DW_TAG_formal_parameter)
>     <9a7b>   DW_AT_name        : nb
>     <9a7e>   DW_AT_decl_file   : 1
>     <9a7f>   DW_AT_decl_line   : 551
>     <9a81>   DW_AT_type        : <0x2a96>
>     <9a85>   DW_AT_location    : 0x172f (location list)
> ...
>     0000172f 0000000000000745 0000000000000750 (DW_OP_reg5 (rdi))
>     0000172f 0000000000000750 0000000000000757 (DW_OP_reg4 (rsi))
>     0000172f 0000000000000757 000000000000075a (DW_OP_GNU_entry_value: (DW_OP_reg5 (rdi)); DW_OP_stack_value)
>     0000172f <End of list>
> -----
> 
> As you can see, the location of the parameter "nb", starts from 0x745
> but unregister_die_notifier() function itself starts from 0x740.

Um, no I can't see. I guess I need to go and read up on DWARF formats.
Any good recommended links?

A quick google gives me:

http://en.wikipedia.org/wiki/DWARF
http://wiki.dwarfstd.org/index.php?title=Dwarf_FAQ
http://www.eagercon.com/dwarf/dwarf-2.0.0.pdf

Is this what you recommend reading? Or is there better documentation?

-- Steve


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