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Re: [PATCH v2 02/10] x86: assembly, FUNC_START for fn, DATA_START for data

From Josh Poimboeuf <jpoimboe@redhat.com>
Newsgroups linux.kernel
Subject Re: [PATCH v2 02/10] x86: assembly, FUNC_START for fn, DATA_START for data
Date 2017-03-22 16:40 +0100
Message-ID <tnQwG-4GP-1@gated-at.bofh.it> (permalink)
References (4 earlier) <tnISt-7c5-11@gated-at.bofh.it> <tnJbP-7m2-1@gated-at.bofh.it> <tnJbQ-7m2-9@gated-at.bofh.it> <tnPhh-3Fu-51@gated-at.bofh.it> <tnQ3D-4lf-7@gated-at.bofh.it>
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On Wed, Mar 22, 2017 at 04:01:08PM +0100, Jiri Slaby wrote:
> On 03/22/2017, 03:11 PM, Josh Poimboeuf wrote:
> > Or, here's a much easier way to do it, without involving objtool:
> > 
> > --- a/include/linux/linkage.h
> > +++ b/include/linux/linkage.h
> > @@ -138,9 +138,17 @@
> >  	name:
> >  #endif
> >  
> > +#ifndef CHECK_DUP_SYM_END
> > +#define CHECK_DUP_SYM_END(name)				\
> > +	.pushsection .discard.sym_func_end ASM_NL	\
> > +	SYM_END_##name: .byte 0 ASM_NL			\
> > +	.popsection
> > +#endif
> > +
> >  /* SYM_END -- use only if you have to */
> >  #ifndef SYM_END
> >  #define SYM_END(name, sym_type)				\
> > +	CHECK_DUP_SYM_END(name) ASM_NL			\
> >  	.type name sym_type ASM_NL			\
> >  	.size name, .-name
> >  #endif
> 
> I tried this approach and it didn't work for me inside .macros. Oh,
> well, the name cannot be first, so now, we can have a check for both
> correct pairing _and_ duplicate ends in one:
> 
> #define SYM_CHECK_START(name)                           \
>         .pushsection .rodata.bubak ASM_NL               \
>         .long has_no_SYM_END_##name - . ASM_NL          \
>         .popsection
> 
> #define SYM_CHECK_END(name)                             \
>         has_no_SYM_END_##name:
> 
> /* SYM_START -- use only if you have to */
> #ifndef SYM_START
> #define SYM_START(name, align, visibility, entry)       \
>         SYM_CHECK_START(name) ASM_NL                    \
>         visibility(name) ASM_NL                         \
>         align ASM_NL                                    \
>         name: ASM_NL                                    \
>         entry
> #endif
> 
> /* SYM_END -- use only if you have to */
> #ifndef SYM_END
> #define SYM_END(name, sym_type, exit)                   \
>         exit ASM_NL                                     \
>         SYM_CHECK_END(name) ASM_NL                      \
>         .type name sym_type ASM_NL                      \
>         .size name, .-name
> #endif
> 
> 
> So for the ftrace mistake I did:
> 
>   AS      arch/x86/kernel/mcount_64.o
> /home/latest/linux/arch/x86/kernel/mcount_64.S: Assembler messages:
> /home/latest/linux/arch/x86/kernel/mcount_64.S:192: Error: symbol
> `has_no_SYM_END_ftrace_caller' is already defined
> 
> 
> or if I remove SYM_END_FUNC completely:
>   LD      vmlinux.o
>   MODPOST vmlinux.o
> arch/x86/built-in.o:(.rodata.bubak+0x130): undefined reference to
> `has_no_SYM_END_ftrace_stub'
> 
> 
> Sad is that this occurs only during linking, so I cannot put it in the
> .discard section -- ideas?

Ah, interesting idea but I can't think of a way to do the missing end
check before link time.

But it would be easy for objtool to check for a missing end because the
symbol would have a zero size.

-- 
Josh

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Thread

Re: [RFC] linkage: new macros for functions and data Ingo Molnar <mingo@kernel.org> - 2017-03-16 09:10 +0100
  Re: [RFC] linkage: new macros for functions and data Jiri Slaby <jslaby@suse.cz> - 2017-03-16 09:20 +0100
    [PATCH v2 07/10] x86: assembly, annotate aliases Jiri Slaby <jslaby@suse.cz> - 2017-03-20 13:40 +0100
    [PATCH v2 04/10] x86: boot, annotate functions properly Jiri Slaby <jslaby@suse.cz> - 2017-03-20 13:40 +0100
    [PATCH v2 09/10] x86: entry, annotate interrupt symbols properly Jiri Slaby <jslaby@suse.cz> - 2017-03-20 13:40 +0100
    [PATCH v2 03/10] x86: assembly, use SYM_FUNC_END for functions Jiri Slaby <jslaby@suse.cz> - 2017-03-20 13:40 +0100
      Re: [PATCH v2 03/10] x86: assembly, use SYM_FUNC_END for functions Josh Poimboeuf <jpoimboe@redhat.com> - 2017-03-21 15:50 +0100
        Re: [PATCH v2 03/10] x86: assembly, use SYM_FUNC_END for functions Ingo Molnar <mingo@kernel.org> - 2017-03-22 08:40 +0100
      Re: [PATCH v2 03/10] x86: assembly, use SYM_FUNC_END for functions Josh Poimboeuf <jpoimboe@redhat.com> - 2017-03-22 15:30 +0100
        Re: [PATCH v2 03/10] x86: assembly, use SYM_FUNC_END for functions Jiri Slaby <jslaby@suse.cz> - 2017-03-22 17:00 +0100
    [PATCH v2 05/10] x86: kernel+lib, annotate local functions Jiri Slaby <jslaby@suse.cz> - 2017-03-20 13:40 +0100
    [PATCH v2 08/10] x86: entry, annotate THUNKs Jiri Slaby <jslaby@suse.cz> - 2017-03-20 13:40 +0100
    [PATCH v2 06/10] x86: crypto, annotate local functions Jiri Slaby <jslaby@suse.cz> - 2017-03-20 13:40 +0100
    [PATCH v2 02/10] x86: assembly, FUNC_START for fn, DATA_START for data Jiri Slaby <jslaby@suse.cz> - 2017-03-20 13:40 +0100
      Re: [PATCH v2 02/10] x86: assembly, FUNC_START for fn, DATA_START  for data Josh Poimboeuf <jpoimboe@redhat.com> - 2017-03-20 14:40 +0100
        Re: [PATCH v2 02/10] x86: assembly, FUNC_START for fn, DATA_START for  data Jiri Slaby <jslaby@suse.cz> - 2017-03-20 16:50 +0100
          Re: [PATCH v2 02/10] x86: assembly, FUNC_START for fn, DATA_START  for data Josh Poimboeuf <jpoimboe@redhat.com> - 2017-03-20 17:10 +0100
      Re: [PATCH v2 02/10] x86: assembly, FUNC_START for fn, DATA_START  for data Pavel Machek <pavel@ucw.cz> - 2017-03-21 15:20 +0100
        Re: [PATCH v2 02/10] x86: assembly, FUNC_START for fn, DATA_START  for data Ingo Molnar <mingo@kernel.org> - 2017-03-22 08:30 +0100
          Re: [PATCH v2 02/10] x86: assembly, FUNC_START for fn, DATA_START for  data Jiri Slaby <jslaby@suse.cz> - 2017-03-22 08:50 +0100
            Re: [PATCH v2 02/10] x86: assembly, FUNC_START for fn, DATA_START  for data Ingo Molnar <mingo@kernel.org> - 2017-03-22 08:50 +0100
              Re: [PATCH v2 02/10] x86: assembly, FUNC_START for fn, DATA_START  for data Josh Poimboeuf <jpoimboe@redhat.com> - 2017-03-22 15:20 +0100
                Re: [PATCH v2 02/10] x86: assembly, FUNC_START for fn, DATA_START for  data Jiri Slaby <jslaby@suse.cz> - 2017-03-22 16:10 +0100
                Re: [PATCH v2 02/10] x86: assembly, FUNC_START for fn, DATA_START  for data Josh Poimboeuf <jpoimboe@redhat.com> - 2017-03-22 16:40 +0100
                Re: [PATCH v2 02/10] x86: assembly, FUNC_START for fn, DATA_START  for data Ingo Molnar <mingo@kernel.org> - 2017-03-23 08:40 +0100
                Re: [PATCH v2 02/10] x86: assembly, FUNC_START for fn, DATA_START  for data Josh Poimboeuf <jpoimboe@redhat.com> - 2017-03-23 14:30 +0100
        Re: [PATCH v2 02/10] x86: assembly, FUNC_START for fn, DATA_START for  data Jiri Slaby <jslaby@suse.cz> - 2017-03-22 13:10 +0100
          Re: [PATCH v2 02/10] x86: assembly, FUNC_START for fn, DATA_START  for data Pavel Machek <pavel@ucw.cz> - 2017-03-22 17:00 +0100
    [RFC v2 10/10] x86: boot, extract efi_pe_entry from startup_64 Jiri Slaby <jslaby@suse.cz> - 2017-03-20 13:40 +0100
    [PATCH v2 01/10] linkage: new macros for assembler symbols Jiri Slaby <jslaby@suse.cz> - 2017-03-20 13:40 +0100

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