[Bug target/109253] libbpf: failed to find BTF info for global/extern symbol '__divdi3'

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109253

--- Comment #3 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jose E. Marchesi <jemarch@gcc.gnu.org>:

https://gcc.gnu.org/g:f31a019d1161ec78846473da743aedf49cca8c27

commit r14-5930-gf31a019d1161ec78846473da743aedf49cca8c27
Author: Jose E. Marchesi <jose.marchesi@oracle.com>
Date:   Fri Nov 24 06:30:28 2023 +0100

    Emit funcall external declarations only if actually used.

    There are many places in GCC where alternative local sequences are
    tried in order to determine what is the cheapest or best alternative
    to use in the current target.  When any of these sequences involve a
    libcall, the current implementation of emit_library_call_value_1
    introduce a side-effect consisting on emitting an external declaration
    for the funcall (such as __divdi3) which is thus emitted even if the
    sequence that does the libcall is not retained.

    This is problematic in targets such as BPF, because the kernel loader
    chokes on the spurious symbol __divdi3 and makes the resulting BPF
    object unloadable.  Note that BPF objects are not linked before being
    loaded.

    This patch changes asssemble_external_libcall to defer emitting
    declarations of external libcall symbols, by saving the call tree
    nodes in a temporary list pending_libcall_symbols and letting
    process_pending_assembly_externals to emit them only if they have been
    referenced.  Solution suggested and sketched by Richard Sandiford.

    Regtested in x86_64-linux-gnu.
    Tested with host x86_64-linux-gnu with target bpf-unknown-none.

    gcc/ChangeLog

            PR target/109253
            * varasm.cc (pending_libcall_symbols): New variable.
            (process_pending_assemble_externals): Process
            pending_libcall_symbols.
            (assemble_external_libcall): Defer emitting external libcall
            symbols to process_pending_assemble_externals.

    gcc/testsuite/ChangeLog

            PR target/109253
            * gcc.target/bpf/divmod-libcall-1.c: New test.
            * gcc.target/bpf/divmod-libcall-2.c: Likewise.
            * gcc.c-torture/compile/libcall-2.c: Likewise.