* perf probe issues
@ 2016-06-14 17:05 Arnaldo Carvalho de Melo
2016-06-15 2:02 ` Masami Hiramatsu
0 siblings, 1 reply; 4+ messages in thread
From: Arnaldo Carvalho de Melo @ 2016-06-14 17:05 UTC (permalink / raw)
To: Masami Hiramatsu; +Cc: Linux Kernel Mailing List
Hi Masami,
While investigating a problem in the annotation code reported by
Linus, with "kaslr" on the kernel command line and this in .config:
[root@jouet ~]# egrep 'CONFIG_(RANDOMIZE_BASE|DEBUG_INFO)' ~acme/git/build/v4.7.0-rc3/.config
CONFIG_RANDOMIZE_BASE=y
# CONFIG_DEBUG_INFO is not set
[root@jouet ~]#
[root@jouet ~]# grep -w vfs_write /proc/kallsyms
ffffffffac2404c0 T vfs_write
[root@jouet ~]# perf probe vfs_write
vfs_write is out of .text, skip it.
Error: Failed to add events.
[root@jouet ~]# perf probe -v vfs_write
probe-definition(0): vfs_write
symbol:vfs_write file:(null) line:0 offset:0 return:0 lazy:(null)
0 arguments
Looking at the vmlinux_path (8 entries long)
Using /lib/modules/4.7.0-rc3/build/vmlinux for symbols
Could not open debuginfo. Try to use symbols.
vfs_write is out of .text, skip it.
Error: Failed to add events. Reason: No such file or directory (Code: -2)
[root@jouet ~]#
Can you try to test with this config to investigate this problem?
We need to improve the error messages, for instance:
"Could not open debuginfo. Try to use symbols."
I think should be rewritten as: "Trying to use kallsyms", no? I.e. if it
doesn't manage to find a vmlinux file, it will try to use kallsyms as a
fallback, is that what is happening here?
- Arnaldo
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: perf probe issues
2016-06-14 17:05 perf probe issues Arnaldo Carvalho de Melo
@ 2016-06-15 2:02 ` Masami Hiramatsu
2016-06-15 17:43 ` Arnaldo Carvalho de Melo
0 siblings, 1 reply; 4+ messages in thread
From: Masami Hiramatsu @ 2016-06-15 2:02 UTC (permalink / raw)
To: Arnaldo Carvalho de Melo; +Cc: Linux Kernel Mailing List
On Tue, 14 Jun 2016 14:05:04 -0300
Arnaldo Carvalho de Melo <acme@kernel.org> wrote:
> Hi Masami,
>
> While investigating a problem in the annotation code reported by
> Linus, with "kaslr" on the kernel command line and this in .config:
>
> [root@jouet ~]# egrep 'CONFIG_(RANDOMIZE_BASE|DEBUG_INFO)' ~acme/git/build/v4.7.0-rc3/.config
> CONFIG_RANDOMIZE_BASE=y
> # CONFIG_DEBUG_INFO is not set
> [root@jouet ~]#
>
> [root@jouet ~]# grep -w vfs_write /proc/kallsyms
> ffffffffac2404c0 T vfs_write
> [root@jouet ~]# perf probe vfs_write
> vfs_write is out of .text, skip it.
> Error: Failed to add events.
> [root@jouet ~]# perf probe -v vfs_write
> probe-definition(0): vfs_write
> symbol:vfs_write file:(null) line:0 offset:0 return:0 lazy:(null)
> 0 arguments
> Looking at the vmlinux_path (8 entries long)
> Using /lib/modules/4.7.0-rc3/build/vmlinux for symbols
> Could not open debuginfo. Try to use symbols.
> vfs_write is out of .text, skip it.
> Error: Failed to add events. Reason: No such file or directory (Code: -2)
> [root@jouet ~]#
>
> Can you try to test with this config to investigate this problem?
Yes, I guess it missed to get start_text because of KASLR...
>
> We need to improve the error messages, for instance:
>
> "Could not open debuginfo. Try to use symbols."
>
> I think should be rewritten as: "Trying to use kallsyms", no? I.e. if it
> doesn't manage to find a vmlinux file, it will try to use kallsyms as a
> fallback, is that what is happening here?
Let me check that the perf symbol/map object uses kallsyms for kernel.
Anyway, if the target is not the kernel, do we change the message
as "trying to use symbols"?
>
> - Arnaldo
--
Masami Hiramatsu <mhiramat@kernel.org>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: perf probe issues
2016-06-15 2:02 ` Masami Hiramatsu
@ 2016-06-15 17:43 ` Arnaldo Carvalho de Melo
2016-06-15 21:33 ` Masami Hiramatsu
0 siblings, 1 reply; 4+ messages in thread
From: Arnaldo Carvalho de Melo @ 2016-06-15 17:43 UTC (permalink / raw)
To: Masami Hiramatsu; +Cc: Linux Kernel Mailing List
Em Wed, Jun 15, 2016 at 11:02:01AM +0900, Masami Hiramatsu escreveu:
> On Tue, 14 Jun 2016 14:05:04 -0300
> Arnaldo Carvalho de Melo <acme@kernel.org> wrote:
> > While investigating a problem in the annotation code reported by
> > Linus, with "kaslr" on the kernel command line and this in .config:
> > [root@jouet ~]# egrep 'CONFIG_(RANDOMIZE_BASE|DEBUG_INFO)' ~acme/git/build/v4.7.0-rc3/.config
> > CONFIG_RANDOMIZE_BASE=y
> > # CONFIG_DEBUG_INFO is not set
> > [root@jouet ~]#
> > [root@jouet ~]# grep -w vfs_write /proc/kallsyms
> > ffffffffac2404c0 T vfs_write
> > [root@jouet ~]# perf probe vfs_write
> > vfs_write is out of .text, skip it.
> > Error: Failed to add events.
> > [root@jouet ~]# perf probe -v vfs_write
> > probe-definition(0): vfs_write
> > symbol:vfs_write file:(null) line:0 offset:0 return:0 lazy:(null)
> > 0 arguments
> > Looking at the vmlinux_path (8 entries long)
> > Using /lib/modules/4.7.0-rc3/build/vmlinux for symbols
> > Could not open debuginfo. Try to use symbols.
> > vfs_write is out of .text, skip it.
> > Error: Failed to add events. Reason: No such file or directory (Code: -2)
> > [root@jouet ~]#
> > Can you try to test with this config to investigate this problem?
> Yes, I guess it missed to get start_text because of KASLR...
> > We need to improve the error messages, for instance:
> > "Could not open debuginfo. Try to use symbols."
> > I think should be rewritten as: "Trying to use kallsyms", no? I.e. if it
> > doesn't manage to find a vmlinux file, it will try to use kallsyms as a
> > fallback, is that what is happening here?
> Let me check that the perf symbol/map object uses kallsyms for kernel.
> Anyway, if the target is not the kernel, do we change the message
> as "trying to use symbols"?
Well, it is _always_ trying to use "symbols" as in "information to map
an address to a symbol", but this information can come from DWARF,
kallsyms, ELF symbol tables, JIT /tmp/ maps, etc :-)
So, if it is going to use kallsyms:
"Trying to use kallsyms"
ELF symtol tables:
"Trying to use the ELF symbol table"
etc.
- Arnaldo
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: perf probe issues
2016-06-15 17:43 ` Arnaldo Carvalho de Melo
@ 2016-06-15 21:33 ` Masami Hiramatsu
0 siblings, 0 replies; 4+ messages in thread
From: Masami Hiramatsu @ 2016-06-15 21:33 UTC (permalink / raw)
To: Arnaldo Carvalho de Melo; +Cc: Linux Kernel Mailing List
On Wed, 15 Jun 2016 14:43:38 -0300
Arnaldo Carvalho de Melo <acme@kernel.org> wrote:
> Em Wed, Jun 15, 2016 at 11:02:01AM +0900, Masami Hiramatsu escreveu:
> > On Tue, 14 Jun 2016 14:05:04 -0300
> > Arnaldo Carvalho de Melo <acme@kernel.org> wrote:
> > > While investigating a problem in the annotation code reported by
> > > Linus, with "kaslr" on the kernel command line and this in .config:
>
> > > [root@jouet ~]# egrep 'CONFIG_(RANDOMIZE_BASE|DEBUG_INFO)' ~acme/git/build/v4.7.0-rc3/.config
> > > CONFIG_RANDOMIZE_BASE=y
> > > # CONFIG_DEBUG_INFO is not set
> > > [root@jouet ~]#
Hmm, could you give me more info? I tried same thing (on Ubuntu 16.04
kernel(4.4 based) which support kaslr by default), but perf probe
succeeded to put an event on vfs_write (I ensured by <debugfs>/kprobes/list).
What would you get if you grep _etext in /proc/kallsyms?
(Ah, perf probe must change error message if it failed to find _etext
from kallsyms...)
>
> > > [root@jouet ~]# grep -w vfs_write /proc/kallsyms
> > > ffffffffac2404c0 T vfs_write
> > > [root@jouet ~]# perf probe vfs_write
> > > vfs_write is out of .text, skip it.
> > > Error: Failed to add events.
> > > [root@jouet ~]# perf probe -v vfs_write
> > > probe-definition(0): vfs_write
> > > symbol:vfs_write file:(null) line:0 offset:0 return:0 lazy:(null)
> > > 0 arguments
> > > Looking at the vmlinux_path (8 entries long)
> > > Using /lib/modules/4.7.0-rc3/build/vmlinux for symbols
> > > Could not open debuginfo. Try to use symbols.
> > > vfs_write is out of .text, skip it.
> > > Error: Failed to add events. Reason: No such file or directory (Code: -2)
> > > [root@jouet ~]#
>
> > > Can you try to test with this config to investigate this problem?
>
> > Yes, I guess it missed to get start_text because of KASLR...
>
> > > We need to improve the error messages, for instance:
>
> > > "Could not open debuginfo. Try to use symbols."
>
> > > I think should be rewritten as: "Trying to use kallsyms", no? I.e. if it
> > > doesn't manage to find a vmlinux file, it will try to use kallsyms as a
> > > fallback, is that what is happening here?
>
> > Let me check that the perf symbol/map object uses kallsyms for kernel.
> > Anyway, if the target is not the kernel, do we change the message
> > as "trying to use symbols"?
>
> Well, it is _always_ trying to use "symbols" as in "information to map
> an address to a symbol", but this information can come from DWARF,
> kallsyms, ELF symbol tables, JIT /tmp/ maps, etc :-)
>
> So, if it is going to use kallsyms:
>
> "Trying to use kallsyms"
>
> ELF symtol tables:
>
> "Trying to use the ELF symbol table"
OK, I'll do that.
>
> etc.
>
> - Arnaldo
--
Masami Hiramatsu <mhiramat@kernel.org>
^ permalink raw reply [flat|nested] 4+ messages in thread
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2016-06-14 17:05 perf probe issues Arnaldo Carvalho de Melo
2016-06-15 2:02 ` Masami Hiramatsu
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2016-06-15 21:33 ` Masami Hiramatsu
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