Re: [gold] enable sorting of text sections with the same prefix

[Ian Lance Taylor <iant at google dot com>]

On Tue, Feb 12, 2013 at 7:01 AM, Alexander Ivchenko <aivchenk@gmail.com> wrote:
> 2013/2/9 Ian Lance Taylor <iant@google.com>:
>> On Fri, Feb 8, 2013 at 5:11 PM, Ian Lance Taylor <iant@google.com> wrote:
>>> On Thu, Feb 7, 2013 at 3:56 AM, Alexander Ivchenko <aivchenk@gmail.com> wrote:
>>>> thank you for your help, Sri. I fixed help string and deleted warning.
>>>>
>>>> Ian, could you please take a look at the attached patch?
>>>
>>> As far as I can see, with this patch, when you use
>>> --sort-section=name, gold will only sort sections that start with
>>> .data. and .bss. by name.  Other sections remain unsorted.  This does
>>> not appear to be what the GNU linker does.  The GNU linker appears to
>>> sort all input sections by name when using --sort-section=name.
>>
>> Sorry, I guess that's not quite right.  You call the sorting code one
>> every section.  But you only set must_sort_attached_input_sections on
>> the .data and .bss sections.  How can you get away with that?
>>
>> Ian
>
> You mean from hardcoding those names (.bss and .data) there? I'm not
> sure so far,
> but I know that BFD sorts them by name when we have -sort-section=name
> and at the
> same time, BFD doesn't sort, say,.sdata and .sbss.
> Do we need to fully mimic the behavior of BFD for this option?

We do not need to fully mimic GNU ld.  However, we need to understand
how and why GNU ld behaves the way it does.  When I look at the GNU ld
code, I don't see anything that restricts the effect of
--sort-section=name to the .data and .bss sections.  Nor is it
documented to behave that way.

The documentation of --sort-section=name for GNU ld is unfortunately
tied to the notion of a default linker script, which gold does not
share.  Still, we ought to be able to come up with some plausible
meaning for gold.  And restricting the behaviour to .data and .bss
does not make sense to me.

Also, in order for this to work correctly, you must call
set_may_sort_attached_input_sections when you create the output
section.  You aren't doing that, and I'm surprised that your code is
working reliably.

Ian