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

[H.J. Lu]

On Sun, Feb 2, 2020 at 5:10 PM Fangrui Song <i@maskray.me> wrote:
>
>
> 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

Oops.  Fixed with this.

Thanks.

-- 
H.J.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 0001-section.c-Fix-typo-in-comments-withe-with.patch
Type: text/x-patch
Size: 1753 bytes
Desc: not available
URL: <https://sourceware.org/pipermail/binutils/attachments/20200203/62461b8e/attachment.bin>