* 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
end of thread, other threads:[~2016-06-15 21:33 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 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 2016-06-15 21:33 ` Masami Hiramatsu
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