linux-kernel - Re: [PATCH 1/2] perf-probe: Ensure debuginfo's build-id is correct

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Message-Id: <20180112012119.224a695b87e106e7bd205da1@kernel.org>
Date:   Fri, 12 Jan 2018 01:21:19 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     mhiramat@...nel.org,
        Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH 1/2] perf-probe: Ensure debuginfo's build-id is correct

On Thu, 11 Jan 2018 12:06:31 -0300
Arnaldo Carvalho de Melo <acme@...nel.org> wrote:

> Em Thu, Jan 11, 2018 at 11:59:32AM -0300, Arnaldo Carvalho de Melo escreveu:
> > Em Thu, Jan 11, 2018 at 09:31:19PM +0900, Masami Hiramatsu escreveu:
> > > On Thu, 4 Jan 2018 13:17:28 -0300
> > > Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
> > > > Em Mon, Dec 18, 2017 at 04:29:03PM +0900, Masami Hiramatsu escreveu:
> > > > > Ensure that the build-id of debuginfo is correctly matched to
> > > > > target build-id, if not, it warns user to check the system
> > > > > debuginfo package is correctly installed.
> 
> > > > So we look at a variety of files looking for one that has a matching
> > > > build-id, I think the warning message should state that the file with
> > > > the unmatched build-id is simply being skipped, no?
> 
> > > Actually, this patch series came from your request that you faced
> > > buildid mismatch between running binary and debuginfo binary, and
> > > you asked me to show the message to tell user what he needs to
> > > check.
> 
> > > > And why do this at 'perf probe -l' time? I.e. at that point whatever
> > > > probes that are in place already have all the needed debug info?
> 
> > > As I pointed, this is not only for perf-probe -l but also perf-probe -a
> > 
> > yeah, I recently noticed this while doind a gdb session, where it warned
> > about buildid mismatches.
>  
> > I'll apply your patch, thanks for working on it!
> 
> Trying to test it, got no warning for the vmlinux case, need to
> investigate, but have not time right now, so, just for documenting it
> here and letting you know:

Thank you for reporting! hmm, I just tested glibc. So I need to
recheck with vmlinux case. Tomorrow I'll investigate it.

Thanks!

> 
> [root@...et ~]# perf probe $verbose "vfs_getname=getname_flags:72 pathname=result->name:string"
> Added new event:
>   probe:vfs_getname    (on getname_flags:72 with pathname=result->name:string)
> 
> You can now use it in all perf tools, such as:
> 
> 	perf record -e probe:vfs_getname -aR sleep 1
> 
> [root@...et ~]# perf probe -l
>   probe:vfs_getname    (on getname_flags:72@...e/git/linux/fs/namei.c with pathname)
> [root@...et ~]# 
> [root@...et ~]# uname -a
> Linux jouet 4.15.0-rc7+ #6 SMP Thu Jan 11 11:39:11 -03 2018 x86_64 x86_64 x86_64 GNU/Linux
> [root@...et ~]# mv /lib/modules/4.15.0-rc7+/build/vmlinux /lib/modules/4.15.0-rc7+/build/vmlinux.OFF
> [root@...et ~]# cp /lib/modules/4.14.0+/build/vmlinux /lib/modules/4.15.0-rc7+/build/vmlinux
> [root@...et ~]# perf probe -l
>   probe:vfs_getname    (on getname_flags+147 with pathname)
> [root@...et ~]# perf probe -v -l
> Opening /sys/kernel/debug/tracing//kprobe_events write=0
> Opening /sys/kernel/debug/tracing//uprobe_events write=0
> Parsing probe_events: p:probe/vfs_getname _text+2601267 pathname=+0(+0(%bx)):string
> Group:probe Event:vfs_getname probe:p
> Looking at the vmlinux_path (8 entries long)
> symsrc__init: build id mismatch for /lib/modules/4.15.0-rc7+/build/vmlinux.
> symsrc__init: cannot get elf header.
> Using /proc/kcore for kernel object code
> Using /proc/kallsyms for symbols
> try to find information at 27b133 in kernel
> Looking at the vmlinux_path (8 entries long)
> symsrc__init: build id mismatch for /lib/modules/4.15.0-rc7+/build/vmlinux.
> Failed to find the path for kernel: No such file or directory
> Failed to find corresponding probes from debuginfo.
>   probe:vfs_getname    (on getname_flags+147 with pathname)
> [root@...et ~]#
> 
> - Arnaldo


-- 
Masami Hiramatsu <mhiramat@...nel.org>