7bdcedd5c8
BPF kfuncs are often not directly referenced and may be inadvertently
removed by optimization steps during kernel builds, thus the __bpf_kfunc
tag mitigates against this removal by including the __used macro. However,
this macro alone does not prevent removal during linking, and may still
yield build warnings (e.g. on mips64el):
[...]
LD vmlinux
BTFIDS vmlinux
WARN: resolve_btfids: unresolved symbol bpf_verify_pkcs7_signature
WARN: resolve_btfids: unresolved symbol bpf_lookup_user_key
WARN: resolve_btfids: unresolved symbol bpf_lookup_system_key
WARN: resolve_btfids: unresolved symbol bpf_key_put
WARN: resolve_btfids: unresolved symbol bpf_iter_task_next
WARN: resolve_btfids: unresolved symbol bpf_iter_css_task_new
WARN: resolve_btfids: unresolved symbol bpf_get_file_xattr
WARN: resolve_btfids: unresolved symbol bpf_ct_insert_entry
WARN: resolve_btfids: unresolved symbol bpf_cgroup_release
WARN: resolve_btfids: unresolved symbol bpf_cgroup_from_id
WARN: resolve_btfids: unresolved symbol bpf_cgroup_acquire
WARN: resolve_btfids: unresolved symbol bpf_arena_free_pages
NM System.map
SORTTAB vmlinux
OBJCOPY vmlinux.32
[...]
Update the __bpf_kfunc tag to better guard against linker optimization by
including the new __retain compiler macro, which fixes the warnings above.
Verify the __retain macro with readelf by checking object flags for 'R':
$ readelf -Wa kernel/trace/bpf_trace.o
Section Headers:
[Nr] Name Type Address Off Size ES Flg Lk Inf Al
[...]
[178] .text.bpf_key_put PROGBITS 00000000 6420 0050 00 AXR 0 0 8
[...]
Key to Flags:
[...]
R (retain), D (mbind), p (processor specific)
Fixes: 57e7c169cd6a ("bpf: Add __bpf_kfunc tag for marking kernel functions as kfuncs")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Tony Ambardar <tony.ambardar@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Jiri Olsa <jolsa@kernel.org>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Cc: Yonghong Song <yonghong.song@linux.dev>
Closes: https://lore.kernel.org/r/202401211357.OCX9yllM-lkp@intel.com/
Link: https://lore.kernel.org/bpf/ZlmGoT9KiYLZd91S@krava/T/
Link: https://lore.kernel.org/bpf/e9c64e9b5c073dabd457ff45128aabcab7630098.1717477560.git.Tony.Ambardar@gmail.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.