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[PATCH v3] elf: Keep unused section symbols for Solaris binary

Fangrui Song maskray@sourceware.org
Wed Dec 10 08:31:46 GMT 2025 
On Mon, Dec 8, 2025 at 11:33 PM Jan Beulich <jbeulich@suse.com> wrote:
>
> On 09.12.2025 08:18, H.J. Lu wrote:
> > On Mon, Dec 8, 2025 at 3:52 PM Jan Beulich <jbeulich@suse.com> wrote:
> >>
> >> On 06.12.2025 04:04, H.J. Lu wrote:
> >>> After
> >>>
> >>> commit d1bcae833b32f1408485ce69f844dcd7ded093a8
> >>> Author: H.J. Lu <hjl.tools@gmail.com>
> >>> Date:   Thu Jan 7 06:42:00 2021 -0800
> >>>
> >>>     ELF: Don't generate unused section symbols
> >>>
> >>> x86 ELF binutils tools no longer generate unused section symbols.  But
> >>> Solaris binary generated by Solaris linker may include symbol sort
> >>> sections which hold indexes of data and function symbols, sorted by name
> >>> or by address.  When objcopy removes section symbols, it corrupts Solaris
> >>> symbol sort sections since symbol indexes are changed.  Keep section
> >>> symbols for Solaris binary.
> >>>
> >>> PR binutils/33684
> >>> * objcopy.c (copy_object): Keep section symbols if input is a
> >>> Solaris binary and output target is the same as input target.
> >>
> >> Hmm, an open-coded OSABI check in objcopy. I was expecting change in libbfd
> >> to e.g. make bfd_keep_unused_section_symbols() on ibfd true for Solaris, to
> >> then copy that property to obfd. Is there a reason to not try to somewhat
> >> abstract what is wanted / needed?
> >
> > Here is the v3 patch with the updated bfd_keep_unused_section_symbols.
> >
> > After
> >
> > commit d1bcae833b32f1408485ce69f844dcd7ded093a8
> > Author: H.J. Lu <hjl.tools@gmail.com>
> > Date:   Thu Jan 7 06:42:00 2021 -0800
> >
> >     ELF: Don't generate unused section symbols
> >
> > x86 ELF binutils tools no longer generate unused section symbols.  But
> > Solaris binary generated by Solaris linker may include symbol sort
> > sections which hold indexes of data and function symbols, sorted by name
> > or by address.  When objcopy removes section symbols, it corrupts Solaris
> > symbol sort sections since symbol indexes are changed.
> >
> > 1. Update bfd_keep_unused_section_symbols to return true for Solaris
> > binary.
> > 2. Keep section symbols if input section symbols should be kept and
> > output target is the same as input target.
>
> This is okay afaic, but please give Rainer and/or Ali a chance to comment.
>
> Irrespective I have a question here, though (perhaps also to Alan and Nick):
> Isn't it wrong for objcopy to remove _any_ symbols (including section ones)
> without an explicit request to do so? IOW shouldn't objcopy without any
> specific options largely generate an output identical to the input?
>
> Jan

Ideally, objcopy would only rewrite the symbol table when absolutely necessary.
Achieving this appears challenging per comments around
https://sourceware.org/bugzilla/show_bug.cgi?id=33684#c16

In related efforts, LLVM's integrated assembler has been removing
unneeded section symbols since 2015.
I reported "gas: Omit unused STT_SECTION symbols"
(https://sourceware.org/bugzilla/show_bug.cgi?id=27109) in 2020. I
appreciate that HJ has implemented this for x86 and hope other ports
will follow suit.
(Elf64_Sym is expensive )
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