From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Thomas Richter <tmricht@linux.ibm.com>,
"linux-perf-use." <linux-perf-users@vger.kernel.org>,
Sumanth Korikkar <sumanthk@linux.ibm.com>,
Heiko Carstens <hca@linux.ibm.com>,
Sven Schnelle <svens@linux.ibm.com>
Subject: Re: Fedora 33 and perf probe failures
Date: Thu, 26 Nov 2020 14:28:49 -0300 [thread overview]
Message-ID: <20201126172849.GE53384@kernel.org> (raw)
In-Reply-To: <20201126220848.e515e3da6921d1512108e3bf@kernel.org>
Em Thu, Nov 26, 2020 at 10:08:48PM +0900, Masami Hiramatsu escreveu:
> Hi Thomas,
>
> I've setup fedora33 and found strange debuginfo.
>
> On Thu, 19 Nov 2020 09:16:57 +0100
> Thomas Richter <tmricht@linux.ibm.com> wrote:
>
> > [root@f33 ~]# perf probe -vvv -L getname_flags
> > Looking at the vmlinux_path (8 entries long)
> > Using /lib/modules/5.9.8-200.fc33.x86_64/build/vmlinux for symbols
> > Open Debuginfo file: /lib/modules/5.9.8-200.fc33.x86_64/build/vmlinux
> > fname: ./include/linux/fs.h, lineno:2527
> > New line range: 2527 to 2147483647
> > path: (null)
> > Specified source line is not found.
> > Error: Failed to show lines. Reason: No such file or directory (Code: -2)
>
> Above error was reproduced, and I found that the perf-probe's routine
> failed to find the real function definition.
>
> I decoded the vmlinux with eu-readelf -w, and I found there were 2
> entries (DIEs) for the getname_flags.
>
> (1)
> [2dbe7c6] subprogram abbrev: 54
> external (flag_present) yes
> name (strp) "getname_flags"
> decl_file (data1) fs.h (8)
> decl_line (data2) 2527
> decl_column (data1) 25
> prototyped (flag_present) yes
> type (ref4) [2dbe7e7]
> sibling (ref4) [2dbe7e7]
> [2dbe7d7] formal_parameter abbrev: 4
> type (ref4) [2da9721]
> [2dbe7dc] formal_parameter abbrev: 4
> type (ref4) [2da97a1]
> [2dbe7e1] formal_parameter abbrev: 4
> type (ref4) [2dabbdd]
>
> (2)
> [2e0fde0] subprogram abbrev: 162
> external (flag_present) yes
> name (strp) "getname_flags"
> decl_file (data1) namei.c (1)
> decl_line (data1) 128
> decl_column (data1) 1
> prototyped (flag_present) yes
> type (ref4) [2dfced6]
> inline (data1) inlined (1)
> sibling (ref4) [2e0fe49]
> [2e0fdf2] formal_parameter abbrev: 31
> name (strp) "filename"
> decl_file (data1) namei.c (1)
> decl_line (data1) 128
> decl_column (data1) 34
> type (ref4) [2de77f3]
> [2e0fdfe] formal_parameter abbrev: 31
> name (strp) "flags"
> decl_file (data1) namei.c (1)
> decl_line (data1) 128
> decl_column (data1) 48
> type (ref4) [2de7873]
> [2e0fe0a] formal_parameter abbrev: 31
> name (strp) "empty"
> decl_file (data1) namei.c (1)
> decl_line (data1) 128
> decl_column (data1) 60
> type (ref4) [2de9ce4]
>
> The first one is not the actual function, but that is a DIE
> for the declaration. However, this DIE doesn't have DW_AT_declaration
> attribute, it should be there if the DIE represents the declaration.
Its a bug in some gdb versions, see:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97060
And here is the pahole cset dealing with that:
https://git.kernel.org/pub/scm/devel/pahole/pahole.git/commit/?h=5a22c2de79fb9edf2d36ff4e8d440a862fc99c2a
> In perf, die_is_func_def() checks that attribute, and if the DIE doen't
> have DW_AT_declaration, line_range_search_cb() think the DIE represents
> the function definition (function prototype). And search the instance
> to find the line range.
>
> However, since the (1) has no DW_AT_declaration, perf probe was mislead
> that the DIE is the function definition, and search the function instance
> which links to the DIE. And it failed to find any instances because
> the DIE it found was just a prototype in the header file. (But it seems
> some call-site DIE refers the declaration DIE.)
>
> Let me try to fix if we skip the first DIE.
>
> Thank you,
>
> --
> Masami Hiramatsu <mhiramat@kernel.org>
--
- Arnaldo
next prev parent reply other threads:[~2020-11-26 17:29 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-18 16:37 Fedora 33 and perf probe failures Thomas Richter
2020-11-19 1:07 ` Masami Hiramatsu
2020-11-19 8:16 ` Thomas Richter
2020-11-19 13:04 ` Masami Hiramatsu
2020-11-26 13:08 ` Masami Hiramatsu
2020-11-26 17:28 ` Arnaldo Carvalho de Melo [this message]
2020-11-27 0:10 ` Masami Hiramatsu
2020-11-27 11:36 ` Arnaldo Carvalho de Melo
2020-11-27 5:48 ` [PATCH 1/2] perf-probe: Fix to die_entrypc() returns error correctly Masami Hiramatsu
2020-11-27 5:48 ` [PATCH 2/2] perf-probe: Change function definition check due to broken dwarf Masami Hiramatsu
2020-11-27 17:36 ` Arnaldo Carvalho de Melo
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