Re: [PATCHv2 1/2] Add is_executable to Dwfl_Module.

Re: [PATCHv2 1/2] Add is_executable to Dwfl_Module.

[Mark Wielaard]

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On Wed, 2014-09-10 at 21:22 +0200, Jan Kratochvil wrote:
> On Wed, 10 Sep 2014 20:56:48 +0200, Mark Wielaard wrote:
> > I don't think it is very helpful or productive to refuse to have a
> > technical opinion on a fair question about a code change you are
> > proposing.
> 
> By ": 1" I give a promise to compiler I will use only its single bit.
> Smart compiler with -fwhole-program, -flto etc. could make it 'unsigned char'
> when the struct is not externally visible and therefore ABI-constrained.

Yeah, I understood why you proposed it for the new field. It was just
pointed out that it was an inconsistent choice with respect to the
existing code/struct.

> libdwfl/
> 2014-09-10  Jan Kratochvil  <jan.kratochvil@redhat.com>
> 
>     * dwfl_build_id_find_elf.c (dwfl_build_id_find_elf): Use IS_EXECUTABLE.
>     * dwfl_segment_report_module.c (dwfl_segment_report_module): Set
>     IS_EXECUTABLE.
>     * libdwflP.h (struct Dwfl_Module): New field is_executable.

I like this cleanup (modulo the already existing e32/e64 confusion in the code).

Thanks,

Mark

[PATCHv2 1/2] Add is_executable to Dwfl_Module.

[Jan Kratochvil]

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On Wed, 10 Sep 2014 20:56:48 +0200, Mark Wielaard wrote:
> I don't think it is very helpful or productive to refuse to have a
> technical opinion on a fair question about a code change you are
> proposing.

By ": 1" I give a promise to compiler I will use only its single bit.
Smart compiler with -fwhole-program, -flto etc. could make it 'unsigned char'
when the struct is not externally visible and therefore ABI-constrained.

But I see in real world the -O2 x86_64 'bool:1' code is much more horrible
compared to plain 'bool' than I expected, so when we already discuss it I have
changed it to 'bool'.
  400406:       88 44 24 e9             mov    %dl,-0x17(%rsp)
vs.
  400400:       0f b6 44 24 e8          movzbl -0x18(%rsp),%eax
  40040b:       c1 e2 03                shl    $0x3,%edx
  40040e:       83 e0 f7                and    $0xfffffff7,%eax
  400411:       09 d0                   or     %edx,%eax
  400413:       88 44 24 e8             mov    %al,-0x18(%rsp)


Thanks,
Jan

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