Gold patch to create separate output sections for certain text section prefixes

[Sriraman Tallam via binutils]

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On Tue, Mar 6, 2018 at 6:24 PM, Cary Coutant <ccoutant@gmail.com> wrote:
>> However, we found out that creating multiple executable ELF segments
>> has other issues as some other tools like symbolizers make assumptions
>> about ELF binaries having just one executable segment and this breaks
>> them.  We are looking at fixing these but an alternate approach gives
>> us flexibility in deploying this.
>
> Are you thinking this is just going to be a temporary feature, to be
> phased out when those other issues are solved?

Thanks for reviewing.  I was hoping this would be permanent as like
you noted these markers are really useful.

>
> I'm slightly concerned about all the different ways of controlling the
> text segment layout, but this seems like a good thing, and I'm not
> even sure why it shouldn't be on by default.

Agreed.

>
>> * layout.cc (Layout::default_section_order): Check for text section
>> prefixes.
>> (Layout::text_section_name_mapping): New static member.
>> (Layout::text_section_name_mapping_count): New static member.
>> (Layout::match_section_name): New static function.
>> (Layout::output_section_name): Check for text section prefixes.
>> * layout.h (Output_section_order::ORDER_TEXT_HOT): New enum value.
>> (Output_section_order::ORDER_TEXT_STARTUP): New enum value.
>> (Output_section_order::ORDER_TEXT_EXIT): New enum value.
>> (Output_section_order::ORDER_TEXT_UNLIKELY): New enum value.
>> (Layout::text_section_name_mapping): New static member.
>> (Layout::text_section_name_mapping_count): New static member.
>> (Layout::match_section_name): New static function.
>> * options.h (keep_text_section_prefix): New -z option.
>> * testsuite/Makefile.am (keep_text_section_prefix): New test.
>> * testsuite/Makefile.in: Regenerate.
>> * testsuite/keep_text_section_prefix.cc: New test source.
>> * testsuite/keep_text_section_prefix.sh: New test script.
>
> +  DEFINE_bool(keep_text_section_prefix, options::DASH_Z, '\0', false,
> +       N_("Keep .text.hot, .text.startup, .text.exit and .text.unlikely "
> + "as separate sections in the final binary."),
> +       N_("Merge all .text.* prefix sections (default)."));
>
> Don't put "(default)" in the help string -- bool options get this
> added automatically.
>
> This is OK with that fix. Thanks! (And sorry for the delay.)
>
> -cary