[Bug ld/30437] aarch64: RELA relocations don't ignore section content as they should

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30437

--- Comment #3 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot 
gnu.org> ---
The master branch has been updated by Michael Matz <matz@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=13a3cad698b3a757b1fcc938cc33e09a364ea47a

commit 13a3cad698b3a757b1fcc938cc33e09a364ea47a
Author: Michael Matz <matz@suse.de>
Date:   Tue May 9 17:48:01 2023 +0200

    PR30437 aarch64: make RELA relocs idempotent

    normally RELA relocs in BFD should not consider the contents of the
    relocated place.  The aarch64 psABI is even stricter, it specifies
    (section 5.7.16) that all RELA relocs _must_ be idempotent.

    Since the inception of the aarch64 BFD backend all the relocs have a
    non-zero src_mask, and hence break this invariant.  It's normally not
    a very visible problem as one can see it only when the relocated place
    already contains a non-zero value, which usually only happens sometimes
    when using 'ld -r' (or as in the testcase when jumping through hoops to
    generate the relocations).  Or with alternative toolchains that do encode
    stuff in the relocated places with the assumption that a relocation
    to that place ignores whatever is there (as they can according to
    the psABI).

    Golang is such a toolchain and https://github.com/golang/go/issues/39927
    is ultimately caused by this problem: the testcase testGCData failing
    is caused by the garbage collection data-structure to describe a type
    containing pointers to be wrong.  It's wrong because a field that's
    supposed to contain a file-relative offset (to some gcbits) has a
    relocation applied and that relocation has an addend which also is
    already part of the go-produced object file (so the addend is
    implicitely applied twice).

    bfd/
            PR ld/30437
            * elfnn-aarch64.c (elfNN_aarch64_howto_table): Clear src_mask
            if all relocation descriptors.

    ld/
            * testsuite/ld-aarch64/rela-idempotent.s: New testcase.
            * testsuite/ld-aarch64/rela-idempotent.d: New.
            * testsuite/ld-aarch64/aarch64-elf.exp: Run it.

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