Re: [PATCH 7/7] DWARF: add the config option

From	"H.J. Lu" <hjl.tools@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 7/7] DWARF: add the config option
Date	2017-05-10 18:30 +0200
Message-ID	<tFCEX-2YC-35@gated-at.bofh.it> (permalink)
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On Wed, May 10, 2017 at 6:09 AM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> On Wed, May 10, 2017 at 10:15:09AM +0200, Jiri Slaby wrote:
>> > I'm, ahem, highly skeptical to creating our own unwinding data
>> > format unless there is *documented, supported, and tested* way to
>> > force the compiler to *automatically* fall back to frame pointers
>> > any time there may be complexity involved,
>>
>> I second this. Inventing a new format like this mostly ends up with
>> using the standard one after several iterations. One cannot think of all
>> the consequences and needs while proposing a new one.
>>
>> The memory footprint is ~2M for average vmlinux. And people who need to
>> access:
>> * either need it frequently -- those do not need performance (LOCKDEP,
>> KASAN, or other debug builds)
>> * or are in the middle of WARNING, BUG, crash, panic or such and this is
>> not that often...
>>
>> And we would need *both*. The limited proprietary one in some sort of
>> .kernel_eh_frame, and DWARF cfis in .debug_frame for tools like crash,
>> gdb and so on.
>
> I don't think so.  DWARF CFI is optimized for size.  My proposal is to
> take the same data (or some subset of it) and reformat it to optimize
> for simplicity.
>
> If, for some reason, we ended up needing *all* the original DWARF data,
> we could still have it in the simpler format.  In that case it might end
> up being 8M instead of 2M :-) But I don't see that being possible.

There is a compact EH for MIPS:

https://github.com/itanium-cxx-abi/cxx-abi/blob/master/MIPSCompactEH.pdf

It can be extended to other targets.

-- 
H.J.

Thread

[PATCH 7/7] DWARF: add the config option Jiri Slaby <jslaby@suse.cz> - 2017-05-05 14:30 +0200
  Re: [PATCH 7/7] DWARF: add the config option Linus Torvalds <torvalds@linux-foundation.org> - 2017-05-05 22:00 +0200
    Re: [PATCH 7/7] DWARF: add the config option Ingo Molnar <mingo@kernel.org> - 2017-05-06 09:30 +0200
      Re: [PATCH 7/7] DWARF: add the config option Jiri Slaby <jslaby@suse.cz> - 2017-05-10 09:50 +0200
    Re: [PATCH 7/7] DWARF: add the config option Jiri Kosina <jikos@kernel.org> - 2017-05-06 16:30 +0200
    Re: [PATCH 7/7] DWARF: add the config option Ingo Molnar <mingo@kernel.org> - 2017-05-07 23:50 +0200
      Re: [PATCH 7/7] DWARF: add the config option Josh Poimboeuf <jpoimboe@redhat.com> - 2017-05-07 23:50 +0200
        Re: [PATCH 7/7] DWARF: add the config option Vojtech Pavlik <vojtech@suse.com> - 2017-05-08 10:20 +0200
          Re: [PATCH 7/7] DWARF: add the config option Josh Poimboeuf <jpoimboe@redhat.com> - 2017-05-08 15:20 +0200
      Re: [PATCH 7/7] DWARF: add the config option hpa@zytor.com - 2017-05-08 00:10 +0200
    Re: [PATCH 7/7] DWARF: add the config option Josh Poimboeuf <jpoimboe@redhat.com> - 2017-05-07 23:50 +0200
      Re: [PATCH 7/7] DWARF: add the config option Andy Lutomirski <luto@amacapital.net> - 2017-05-08 07:40 +0200
        Re: [PATCH 7/7] DWARF: add the config option Ingo Molnar <mingo@kernel.org> - 2017-05-08 08:20 +0200
        Re: [PATCH 7/7] DWARF: add the config option Josh Poimboeuf <jpoimboe@redhat.com> - 2017-05-08 16:50 +0200
          Re: [PATCH 7/7] DWARF: add the config option hpa@zytor.com - 2017-05-08 21:10 +0200
      Re: [PATCH 7/7] DWARF: add the config option Andy Lutomirski <luto@kernel.org> - 2017-05-09 02:30 +0200
        Re: [PATCH 7/7] DWARF: add the config option Josh Poimboeuf <jpoimboe@redhat.com> - 2017-05-09 03:40 +0200
          Re: [PATCH 7/7] DWARF: add the config option Andy Lutomirski <luto@kernel.org> - 2017-05-09 04:40 +0200
            Re: [PATCH 7/7] DWARF: add the config option Josh Poimboeuf <jpoimboe@redhat.com> - 2017-05-09 05:40 +0200
              Re: [PATCH 7/7] DWARF: add the config option hpa@zytor.com - 2017-05-09 12:10 +0200
                Re: [PATCH 7/7] DWARF: add the config option Josh Poimboeuf <jpoimboe@redhat.com> - 2017-05-09 17:00 +0200
                Re: [PATCH 7/7] DWARF: add the config option "H.J. Lu" <hjl.tools@gmail.com> - 2017-05-09 18:50 +0200
                Re: [PATCH 7/7] DWARF: add the config option Jiri Slaby <jslaby@suse.cz> - 2017-05-10 10:20 +0200
                Re: [PATCH 7/7] DWARF: add the config option Josh Poimboeuf <jpoimboe@redhat.com> - 2017-05-10 15:10 +0200
                Re: [PATCH 7/7] DWARF: add the config option "H.J. Lu" <hjl.tools@gmail.com> - 2017-05-10 18:30 +0200
      Re: [PATCH 7/7] DWARF: add the config option Jiri Kosina <jikos@kernel.org> - 2017-05-09 20:50 +0200
        Re: [PATCH 7/7] DWARF: add the config option Josh Poimboeuf <jpoimboe@redhat.com> - 2017-05-09 21:30 +0200
          Re: [PATCH 7/7] DWARF: add the config option Jiri Slaby <jslaby@suse.cz> - 2017-05-10 10:40 +0200
            Re: [PATCH 7/7] DWARF: add the config option Josh Poimboeuf <jpoimboe@redhat.com> - 2017-05-10 15:20 +0200
    Re: [PATCH 7/7] DWARF: add the config option Jiri Slaby <jslaby@suse.cz> - 2017-05-10 09:50 +0200
      Re: [PATCH 7/7] DWARF: add the config option Josh Poimboeuf <jpoimboe@redhat.com> - 2017-05-10 14:50 +0200
        Re: [PATCH 7/7] DWARF: add the config option Jiri Slaby <jslaby@suse.cz> - 2017-05-10 14:50 +0200
      Re: [PATCH 7/7] DWARF: add the config option Linus Torvalds <torvalds@linux-foundation.org> - 2017-05-10 20:20 +0200

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