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SubjectRe: [tip:perf/urgent] perf symbols: Handle /proc/sys/kernel/kptr_restrict
Em Thu, May 26, 2011 at 09:39:46PM +0200, Ingo Molnar escreveu:
>
> * tip-bot for Arnaldo Carvalho de Melo <acme@redhat.com> wrote:
>
> > Commit-ID: ec80fde746e3ccf93895d25ae1a7071c9af52585
> > Gitweb: http://git.kernel.org/tip/ec80fde746e3ccf93895d25ae1a7071c9af52585
> > Author: Arnaldo Carvalho de Melo <acme@redhat.com>
> > AuthorDate: Thu, 26 May 2011 09:53:51 -0300
> > Committer: Arnaldo Carvalho de Melo <acme@redhat.com>
> > CommitDate: Thu, 26 May 2011 11:15:25 -0300
> >
> > perf symbols: Handle /proc/sys/kernel/kptr_restrict
>
> Ok, things are much better now with kptr_restrict turned on - but i
> still see a few rough edges in practice.
>
> For example 'perf top' says:
>
> aldebaran:~/linux> perf top
> [kernel.kallsyms] with build id 122214021a666675f6e5ff97d70a85ce7139c0e7 not found, continuing without symbols
> The (null) file can't be used

please wait a bit more, I completely forgot testing 'perf top' :-\

> Now we've confused the user, havent we? :-)
>
> Also, if i run 'perf top' with the proper vmlinux in the cwd, i do
> not get any warning messages - despite both module symbols not being
> available and potetial relocations not being considered.

Right, it has to provide similar warning.

> Secondly, even though i have the proper 'vmlinux' in cwd, i get half
> a page long warnings on perf record warning me about the vmlinux:
>
> WARNING: Kernel address maps (/proc/{kallsyms,modules}) are restricted, check /proc/sys/kernel/kptr_restrict.
>
> Samples in kernel functions may not be resolved if a suitable
> vmlinux file is not found in the buildid cache or in the vmlinux
> path.
>
> ...
>
> But a vmlinux file *is* in the cwd.
>
> One detail i noticed in the patch:
>
> > symbol__init();
> >
> > + if (symbol_conf.kptr_restrict)
> > + pr_warning("WARNING: Kernel address maps "
> > + "(/proc/{kallsyms,modules}) are restricted, "
> > + "check /proc/sys/kernel/kptr_restrict.\n\n"
> > + "Samples in kernel functions may not be resolved "
> > + "if a suitable vmlinux file is not found in the "
> > + "buildid cache or in the vmlinux path.\n\n"
> > + "Samples in kernel modules won't be resolved "
> > + "at all.\n\n"
> > + "If some relocation was applied (e.g. kexec) "
> > + "symbols may be misresolved even with a suitable "
> > + "vmlinux or kallsyms file.\n\n");
>
>
> messages broken mid-line just to make it look better is really bad
> and can break git grep searches for the string as seen on the screen,
> such as:
>
> git grep="are restricted, check"
>
> The solution i use in such cases is to deviate in a common-sense way
> from the standard coding style:
>
> if (symbol_conf.kptr_restrict) {
> pr_warning(
> "WARNING: Kernel address maps (/proc/{kallsyms,modules}) are restricted, check /proc/sys/kernel/kptr_restrict.\n\n"
> "Samples in kernel functions may not be resolved if a suitable vmlinux file is not found in the buildid cache or in the vmlinux path.\n\n"
> "Samples in kernel modules won't be resolved at all.\n\n"
> "If some relocation was applied (e.g. kexec) symbols may be misresolved even with a suitable vmlinux or kallsyms file.\n\n");
> }
>
> This has the big advantage that you can check how the *user* will see
> this message.
>
> Had you done this you'd have immediately noticed that the individual
> lines are *way* too large to fit on even large terminals. Please
> break such messages in a much shorter fashion - we want the error
> messages we output to be readable even on relatively small (80col)
> terminals.

But it would reflow, no?

> Thanks,
>
> Ingo


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