[Bug debug/112849] btf: wrong BTF_KIND_DATSEC entries for extern variables without known section

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112849

--- Comment #3 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by David Faust <dfaust@gcc.gnu.org>:

https://gcc.gnu.org/g:b8cf266f4ca4ff89704b190c827abf9ea7e7b5bf

commit r14-6195-gb8cf266f4ca4ff89704b190c827abf9ea7e7b5bf
Author: David Faust <david.faust@oracle.com>
Date:   Mon Dec 4 14:08:03 2023 -0800

    btf: avoid wrong DATASEC entries for extern vars [PR112849]

    The process of creating BTF_KIND_DATASEC records involves iterating
    through variable declarations, determining which section they will be
    placed in, and creating an entry in the appropriate DATASEC record
    accordingly.

    For variables without e.g. an explicit __attribute__((section)), we use
    categorize_decl_for_section () to identify the appropriate named section
    and corresponding BTF_KIND_DATASEC record.

    This was incorrectly being done for 'extern' variable declarations as
    well as non-extern ones, which meant that extern variable declarations
    could result in BTF_KIND_DATASEC entries claiming the variable is
    allocated in some section such as '.bss' without any knowledge whether
    that is actually true. That resulted in errors building the Linux kernel
    BPF selftests.

    This patch corrects btf_collect_datasec () to avoid assuming a section
    for extern variables, and only emit BTF_KIND_DATASEC entries for them if
    they have a known section.

    gcc/
            PR debug/112849
            * btfout.cc (btf_collect_datasec): Avoid incorrectly creating an
            entry in a BTF_KIND_DATASEC record for extern variable decls
without
            a known section.

    gcc/testsuite/
            PR debug/112849
            * gcc.dg/debug/btf/btf-datasec-3.c: New test.