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Re: [RFC PATCH 05/10] objtool, x86: add facility for asm code to provide CFI hints

From Andy Lutomirski <luto@kernel.org>
Newsgroups linux.kernel
Subject Re: [RFC PATCH 05/10] objtool, x86: add facility for asm code to provide CFI hints
Date 2017-06-01 16:00 +0200
Message-ID <tNyNP-3fE-7@gated-at.bofh.it> (permalink)
References <tNr9D-6Ua-3@gated-at.bofh.it> <tNr9E-6Ua-9@gated-at.bofh.it>
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On Wed, May 31, 2017 at 10:44 PM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> Some asm (and inline asm) code does special things to the stack which
> objtool can't understand.  (Nor can GCC or GNU assembler, for that
> matter.)  In such cases we need a facility for the code to provide
> annotations, so the unwinder can unwind through it.
>
> This provides such a facility, in the form of CFI hints.  They're
> similar to the GNU assembler .cfi* directives, but they give more
> information, and are needed in far fewer places, because objtool can
> fill in the blanks by following branches and adjusting the stack pointer
> for pushes and pops.

Two minor suggestions:

Could you prefix these with something other than "CFI_"?  For those of
use who have read the binutils manual, using "CFI_" sounds awfully
like .cfi_, and people might expect the semantics to be the same.

> +#define CFI_HINT(cfa_reg, cfa_offset, type)                    \
> +       "999: \n\t"                                             \

Have you checked if 999 is used elsewhere?  My personal preference is to use:

.Ldescriptive_text_\@:

instead of a hopefully-unique number.  I never researched the history,
but I suspect that the convention of using large numbers came from
early binutils versions that didn't have \@, but we use \@ fairly
extensively in the kernel these days, so it would seem that we no
longer support binutils versions that old.

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[RFC PATCH 00/10] x86: undwarf unwinder Josh Poimboeuf <jpoimboe@redhat.com> - 2017-06-01 07:50 +0200
  [RFC PATCH 06/10] x86/entry: add CFI hint undwarf annotations Josh Poimboeuf <jpoimboe@redhat.com> - 2017-06-01 07:50 +0200
    Re: [RFC PATCH 06/10] x86/entry: add CFI hint undwarf annotations Andy Lutomirski <luto@kernel.org> - 2017-06-01 16:10 +0200
      Re: [RFC PATCH 06/10] x86/entry: add CFI hint undwarf annotations Josh Poimboeuf <jpoimboe@redhat.com> - 2017-06-01 16:30 +0200
        Re: [RFC PATCH 06/10] x86/entry: add CFI hint undwarf annotations Josh Poimboeuf <jpoimboe@redhat.com> - 2017-06-01 16:30 +0200
          Re: [RFC PATCH 06/10] x86/entry: add CFI hint undwarf annotations Andy Lutomirski <luto@kernel.org> - 2017-06-01 16:50 +0200
            Re: [RFC PATCH 06/10] x86/entry: add CFI hint undwarf annotations Josh Poimboeuf <jpoimboe@redhat.com> - 2017-06-01 17:10 +0200
  [RFC PATCH 09/10] extable: add undwarf table sorting ability to sorttable script Josh Poimboeuf <jpoimboe@redhat.com> - 2017-06-01 07:50 +0200
  [RFC PATCH 08/10] extable: rename 'sortextable' script to 'sorttable' Josh Poimboeuf <jpoimboe@redhat.com> - 2017-06-01 07:50 +0200
  [RFC PATCH 05/10] objtool, x86: add facility for asm code to provide CFI hints Josh Poimboeuf <jpoimboe@redhat.com> - 2017-06-01 07:50 +0200
    Re: [RFC PATCH 05/10] objtool, x86: add facility for asm code to  provide CFI hints Andy Lutomirski <luto@kernel.org> - 2017-06-01 16:00 +0200
      Re: [RFC PATCH 05/10] objtool, x86: add facility for asm code to  provide CFI hints Josh Poimboeuf <jpoimboe@redhat.com> - 2017-06-01 16:20 +0200
        Re: [RFC PATCH 05/10] objtool, x86: add facility for asm code to  provide CFI hints Andy Lutomirski <luto@kernel.org> - 2017-06-01 16:50 +0200
          Re: [RFC PATCH 05/10] objtool, x86: add facility for asm code to  provide CFI hints Josh Poimboeuf <jpoimboe@redhat.com> - 2017-06-01 17:10 +0200
  [RFC PATCH 01/10] objtool: move checking code to check.c Josh Poimboeuf <jpoimboe@redhat.com> - 2017-06-01 07:50 +0200
  [RFC PATCH 07/10] x86/asm: add CFI hint annotations to sync_core() Josh Poimboeuf <jpoimboe@redhat.com> - 2017-06-01 07:50 +0200
  [RFC PATCH 04/10] objtool: add undwarf debuginfo generation Josh Poimboeuf <jpoimboe@redhat.com> - 2017-06-01 07:50 +0200
  [RFC PATCH 10/10] x86/unwind: add undwarf unwinder Josh Poimboeuf <jpoimboe@redhat.com> - 2017-06-01 07:50 +0200
    Re: [RFC PATCH 10/10] x86/unwind: add undwarf unwinder Peter Zijlstra <peterz@infradead.org> - 2017-06-01 13:10 +0200
      Re: [RFC PATCH 10/10] x86/unwind: add undwarf unwinder Josh Poimboeuf <jpoimboe@redhat.com> - 2017-06-01 14:30 +0200
        Re: [RFC PATCH 10/10] x86/unwind: add undwarf unwinder Jiri Slaby <jslaby@suse.cz> - 2017-06-01 14:50 +0200
          Re: [RFC PATCH 10/10] x86/unwind: add undwarf unwinder Josh Poimboeuf <jpoimboe@redhat.com> - 2017-06-01 15:10 +0200
          Re: [RFC PATCH 10/10] x86/unwind: add undwarf unwinder Peter Zijlstra <peterz@infradead.org> - 2017-06-01 15:50 +0200
        Re: [RFC PATCH 10/10] x86/unwind: add undwarf unwinder Peter Zijlstra <peterz@infradead.org> - 2017-06-01 15:20 +0200
    Re: [RFC PATCH 10/10] x86/unwind: add undwarf unwinder Peter Zijlstra <peterz@infradead.org> - 2017-06-01 14:20 +0200
      Re: [RFC PATCH 10/10] x86/unwind: add undwarf unwinder Josh Poimboeuf <jpoimboe@redhat.com> - 2017-06-01 14:40 +0200
        Re: [RFC PATCH 10/10] x86/unwind: add undwarf unwinder Peter Zijlstra <peterz@infradead.org> - 2017-06-01 15:20 +0200
          Re: [RFC PATCH 10/10] x86/unwind: add undwarf unwinder Josh Poimboeuf <jpoimboe@redhat.com> - 2017-06-01 17:10 +0200
  [RFC PATCH 02/10] objtool, x86: add several functions and files to the objtool whitelist Josh Poimboeuf <jpoimboe@redhat.com> - 2017-06-01 07:50 +0200
  Re: [RFC PATCH 00/10] x86: undwarf unwinder Ingo Molnar <mingo@kernel.org> - 2017-06-01 08:10 +0200
    Re: [RFC PATCH 00/10] x86: undwarf unwinder Josh Poimboeuf <jpoimboe@redhat.com> - 2017-06-01 14:00 +0200
      Re: [RFC PATCH 00/10] x86: undwarf unwinder Peter Zijlstra <peterz@infradead.org> - 2017-06-01 14:20 +0200
        Re: [RFC PATCH 00/10] x86: undwarf unwinder Jiri Slaby <jslaby@suse.cz> - 2017-06-01 14:40 +0200
          Re: [RFC PATCH 00/10] x86: undwarf unwinder Jiri Slaby <jslaby@suse.cz> - 2017-06-01 15:00 +0200
          Re: [RFC PATCH 00/10] x86: undwarf unwinder Josh Poimboeuf <jpoimboe@redhat.com> - 2017-06-01 15:00 +0200
        Re: [RFC PATCH 00/10] x86: undwarf unwinder Josh Poimboeuf <jpoimboe@redhat.com> - 2017-06-01 14:50 +0200
          Re: [RFC PATCH 00/10] x86: undwarf unwinder Peter Zijlstra <peterz@infradead.org> - 2017-06-01 15:30 +0200
            Re: [RFC PATCH 00/10] x86: undwarf unwinder Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-06-06 16:20 +0200
          Re: [RFC PATCH 00/10] x86: undwarf unwinder Andy Lutomirski <luto@kernel.org> - 2017-06-01 16:00 +0200
      Re: [RFC PATCH 00/10] x86: undwarf unwinder Ingo Molnar <mingo@kernel.org> - 2017-06-01 16:00 +0200
        Re: [RFC PATCH 00/10] x86: undwarf unwinder Jiri Slaby <jslaby@suse.cz> - 2017-06-01 16:00 +0200
          Re: [RFC PATCH 00/10] x86: undwarf unwinder Jiri Slaby <jslaby@suse.cz> - 2017-06-02 10:40 +0200
        Re: [RFC PATCH 00/10] x86: undwarf unwinder Josh Poimboeuf <jpoimboe@redhat.com> - 2017-06-01 16:10 +0200
        Re: [RFC PATCH 00/10] x86: undwarf unwinder Jiri Slaby <jslaby@suse.cz> - 2017-06-01 16:10 +0200
          Re: [RFC PATCH 00/10] x86: undwarf unwinder Mel Gorman <mgorman@suse.de> - 2017-06-02 12:50 +0200

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