[Bug target/48097] gcc sometimes generates code that uses the buggy libgcc_s unwinder on darwin (originally exposed by Throw_2 failures in libjava testsuite under Xcode 4.0)

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=48097

--- Comment #18 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Iain D Sandoe <iains@gcc.gnu.org>:

https://gcc.gnu.org/g:491d5b3cf8216f9285a67aa213b9a66b0035137b

commit r11-7443-g491d5b3cf8216f9285a67aa213b9a66b0035137b
Author: Iain Sandoe <iain@sandoe.co.uk>
Date:   Mon Jan 18 20:09:10 2021 +0000

    dwarf2unwind : Force the CFA after remember/restore pairs [44107/48097].

    This address one of the more long-standing and serious regressions
    for Darwin.  GCC emits unwind code by default on the assumption that
    the unwinder will be (of have the same capability) as the one in the
    current libgcc_s.  For Darwin platforms, this is not the case - some
    of them are based on the libgcc_s from GCC-4.2.1 and some are using
    the unwinder provided by libunwind (part of the LLVM project). The
    latter implementation has gradually adopted a section that deals with
    GNU unwind.

    The most serious problem for some of the platform versions is in
    handling DW_CFA_remember/restore_state pairs.  The DWARF description
    talks about these in terms of saving/restoring register rows; this is
    what GCC originally did (and is what the unwinders do for the Darwin
    versions based on libgcc_s).

    However, in r118068, this was changed so that not only the registers
    but also the current frame address expression were saved.  The unwind
    code assumes that the unwinder will do this; some of Darwin's unwinders
    do not, leading to lockups etc.  To date, the only solution has been
    to replace the system libgcc_s with a newer one which is not a viable
    solution for many end-users (since that means overwritting the one
    provided with the system installation).

    The fix here provides a target hook that allows the target to specify
    that the CFA should be reinstated after a DW_CFA_restore.  This fixes
    the issue (and also the closed WONTFIX of 44107).

    (As a matter of record, it also fixes reported Java issues if
     backported to GCC-5).

    gcc/ChangeLog:

            PR target/44107
            PR target/48097
            * config/darwin-protos.h (darwin_should_restore_cfa_state): New.
            * config/darwin.c (darwin_should_restore_cfa_state): New.
            * config/darwin.h (TARGET_ASM_SHOULD_RESTORE_CFA_STATE): New.
            * doc/tm.texi: Regenerated.
            * doc/tm.texi.in: Document TARGET_ASM_SHOULD_RESTORE_CFA_STATE.
            * dwarf2cfi.c (connect_traces): If the target requests, restore
            the CFA expression after a DW_CFA_restore.
            * target.def (TARGET_ASM_SHOULD_RESTORE_CFA_STATE): New hook.