Re: Fedora 33 and perf probe failures

[Masami Hiramatsu <mhiramat@kernel.org>]

On Thu, 26 Nov 2020 14:28:49 -0300
Arnaldo Carvalho de Melo <acme@kernel.org> wrote:

> 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

Thanks, so there is a compiler bug.

> 
> And here is the pahole cset dealing with that:
> 
> https://git.kernel.org/pub/scm/devel/pahole/pahole.git/commit/?h=5a22c2de79fb9edf2d36ff4e8d440a862fc99c2a

Oh, that's nice!

Anyway, I found how I can handle it for --lines option.
Let me fix it first.

Thank you,


-- 
Masami Hiramatsu <mhiramat@kernel.org>