[Bug ld/28827] [2.38 Regression] ld hits assertion building LLVM 9 on powerpc64le-linux-gnu

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=28827

--- Comment #11 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot 
gnu.org> ---
The binutils-2_38-branch branch has been updated by Alan Modra
<amodra@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=d3ec1c514429b8c695974e785e47af8f71c388a2

commit d3ec1c514429b8c695974e785e47af8f71c388a2
Author: Alan Modra <amodra@gmail.com>
Date:   Fri Jan 28 09:46:13 2022 +1030

    PR28827, assertion building LLVM 9 on powerpc64le-linux-gnu

    The assertion is this one in ppc_build_one_stub
      BFD_ASSERT (stub_entry->stub_offset >=
stub_entry->group->stub_sec->size);
    It is checking that a stub doesn't overwrite the tail of a previous
    stub, so not something trivial.

    Normally, stub sizing iterates until no stubs are added, detected by
    no change in stub section size.  Iteration also continues if no stubs
    are added but one or more stubs increases in size, which also can be
    detected by a change in stub section size.  But there is a
    pathological case where stub section sizing decreases one iteration
    then increases the next.  To handle that situation, stub sizing also
    stops at more than STUB_SHRINK_ITER (20) iterations when calculated
    stub section size is smaller.  The previous larger size is kept for
    the actual layout (so that building the stubs, which behaves like
    another iteration of stub sizing, will see the stub section sizes
    shrink).  The problem with that stopping condition is that it assumes
    that stub sizing is only affected by addresses external to the stub
    sections, which isn't always true.

    This patch fixes that by also keeping larger individual stub_offset
    addresses past STUB_SHRINK_ITER.  It also catches a further
    pathological case where one stub shrinks and another expands in such a
    way that no stub section size change is seen.

            PR 28827
            * elf64-ppc.c (struct ppc_link_hash_table): Add stub_changed.
            (STUB_SHRINK_ITER): Move earlier in file.
            (ppc_size_one_stub): Detect any change in stub_offset.  Keep
            larger one if past STUB_SHRINK_ITER.
            (ppc64_elf_size_stubs): Iterate on stub_changed too.

    (cherry picked from commit 0441f94fba61998b4bd18487aacf70a672df099c)

    Re: PR28827, assertion building LLVM 9 on powerpc64le-linux-gnu

    The previous patch wasn't quite correct.  The size and padding depends
    on offset used in the current iteration, and if we're fudging the
    offset past STUB_SHRINK_ITER then we'd better use that offset.  We
    can't have plt_stub_pad using stub_sec->size as the offset.

            PR 28827
            * elf64-ppc.c (plt_stub_pad): Add stub_off param.
            (ppc_size_one_stub): Set up stub_offset to value used in this
            iteration before sizing the stub.  Adjust plt_stub_pad calls.

    (cherry picked from commit 2405fc4016feadea33cb747d5654514f62b74ff4)

    Re: PR28827, assertion building LLVM 9 on powerpc64le-linux-gnu

    In trying to find a testcase for PR28827, I managed to hit a linker
    error in bfd_set_section_contents with a .branch_lt input section
    being too large for the output .branch_lt.

    bfd/
            PR 28827
            * elf64-ppc.c (ppc64_elf_size_stubs): Set section size to
            maxsize past STUB_SHRINK_ITER before laying out.  Remove now
            unnecessary conditional setting of maxsize at start of loop.
    ld/
            * testsuite/ld-powerpc/pr28827-2.d,
            * testsuite/ld-powerpc/pr28827-2.lnk,
            * testsuite/ld-powerpc/pr28827-2.s: New test.
            * testsuite/ld-powerpc/powerpc.exp: Run it.

    (cherry picked from commit 9ff8aa7d418bc508dbd429576b93e30ed9dc5891)

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