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[Bug ld/28143] New: start-stop-gc feature addition broke link with ldscr

From: andy at omniosce dot org
Subject: [Bug ld/28143] New: start-stop-gc feature addition broke link with ldscript
Date: Mon, 26 Jul 2021 11:55:26 +0000


            Bug ID: 28143
           Summary: start-stop-gc feature addition broke link with
           Product: binutils
           Version: 2.37
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: ld
          Assignee: unassigned at sourceware dot org
          Reporter: andy at omniosce dot org
  Target Milestone: ---

Updating to binutils 2.37 has broken the build of the boot loader in the
illumos project.

The loader uses linker sets to implement its internal commands, and ld in
binutils 2.37 is stripping the command symbols where it did not before, with no
change in linker options.

The loader is built with an ldscript which contains:

        .data :
                __start_set_Xcommand_set = .;
                __stop_set_Xcommand_set = .;

and the linker is invoked with:

    static -T ldscript -N --gc-sections

an example of a symbol which was present with ld from binutils 2.36.1 but is
now stripped:

      [65]  0x00063de0 0x00000004  OBJT LOCL  D    0 .data         

additionally, the visibility of the __start and __stop symbols has changed from
protected to default.

    - [1943]  0x00063e50 0x00000000  NOTY GLOB  P    0 .data         
    + [2232]  0x0005dd80 0x00000000  NOTY GLOB  D    0 .data         

Adding KEEP(*(set_Xcommand_set)) to the ldscript stops the symbols from being
stripped, but the visibility change for __start/__stop is still happening.

I used git bisect to narrow down this change in behaviour to the commit which
introduced -z start-stop-gc
(https://sourceware.org/bugzilla/show_bug.cgi?id=27451 )

The commit message for that includes:

    (bfd_elf_define_start_stop): Don't modify ldscript_def syms.

and I see a couple of additional tests for ldscript being added here - removing
those restores previous behaviour.

was this change in behaviour around ldscripts intentional or is this a bug?

Note - there's no difference in output with -z start-stop-gc and -z


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