Re: [PATCH] ELF: Add support for unique section ID to assembler

[Fangrui Song <i at maskray dot me>]

On 2020-02-02, H.J. Lu wrote:
> On Sun, Feb 2, 2020@4:22 PM Alan Modra <amodra@gmail.com> wrote:
> > On Sun, Feb 02, 2020@09:50:54AM -0800, H.J. Lu wrote:
> > > Clang's integrated assembler supports multiple section with the same
> > > name:
> > >
> > >       .section .text,"ax",@progbits,unique,1
> > >       nop
> > >       .section .text,"ax",@progbits,unique,2
> > >       nop
> > >
> > > "unique,N" assigns the number, N, as the section ID, to a section.  The
> > > valid values of the section ID are between 0 and 4294967295.  It can be
> > > used to distinguish different sections with the same section name.
> > >
> > > This is useful with -fno-unique-section-names -ffunction-sections.
> > > -ffunction-sections by default generates .text.foo, .text.bar, etc.
> > > Using the same string can save lots of space in .strtab.
> > >
> > > This patch adds section_id to bfd_section and reuses the linker
> > > internal bit in BFD section flags, SEC_LINKER_CREATED, for assmebler
> > > internal use to mark valid section_id.  It also updates objdump to
> > > compare section pointers if 2 sections comes from the same file since
> > > 2 different sections can have the same section name.
> >
> > Looks OK to me.
>
> This is the patch I am checking in.  I updated documentation with
>
> iff --git a/gas/doc/as.texi b/gas/doc/as.texi
> index fa155096159..152bbfdd009 100644
> --- a/gas/doc/as.texi
> +++ b/gas/doc/as.texi
> @@ -6709,6 +6709,18 @@ this directive.  If that section used @code{G}, then the
> new section will use
> @code{G} with those same @var{GroupName} and @var{linkage} fields implicitly.
> If not, then the @code{?} symbol has no effect.
>
> +The optional @var{unique,@code{<number>}} argument must come last.  It
> +assigns @var{@code{<number>}} as a unique section ID to distinguish
> +different sections with the same section name like these:
> +
> +@smallexample
> +.section @var{name},"@var{flags}",@@@var{type},@var{unique,@code{<number>}}
> +.section @var{name},"@var{flags}"G,@@@var{type},@var{GroupName},[@var{linkage}]
> ,@var{unique,@code{<number>}}
> +.section @var{name},"@var{flags}"MG,@@@var{type},@var{entsize},@var{GroupName}[
> ,@var{linkage}],@var{unique,@code{<number>}}
> +@end smallexample
> +
> +The valid values of @var{@code{<number>}} are between 0 and 4294967295.
> +
> If no flags are specified, the default flags depend upon the section name.  If
> the section name is not recognized, the default will be for the section to have
> none of the above flags: it will not be allocated in memory, nor writable, nor
>
>
> --
> H.J.

Thanks for the patch! Looks good.

+     sections withe the same section name.  */

Typo. withe -> with