linux-kernel - [PATCH v2 0/3] Fix -Wmaybe-uninitialized warnings/errors

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Message-ID: <20241022172329.3871958-1-ezulian@redhat.com>
Date: Tue, 22 Oct 2024 19:23:26 +0200
From: Eder Zulian <ezulian@...hat.com>
To: bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: ast@...nel.org,
	daniel@...earbox.net,
	andrii@...nel.org,
	martin.lau@...ux.dev,
	eddyz87@...il.com,
	song@...nel.org,
	yonghong.song@...ux.dev,
	john.fastabend@...il.com,
	kpsingh@...nel.org,
	sdf@...ichev.me,
	haoluo@...gle.com,
	jolsa@...nel.org,
	acme@...hat.com,
	vmalik@...hat.com,
	williams@...hat.com
Subject: [PATCH v2 0/3] Fix -Wmaybe-uninitialized warnings/errors

Hello!

This v2 series initializes the variables 'set' and 'set8' in sets_patch to
NULL, along with the variables 'new_off' and 'pad_bits' and 'pad_type' in
btf_dump_emit_bit_padding to zero or NULL according to their types and the
variable 'o' in options__order to NULL to prevent compiler warnings/errors
which are observed when compiling with non-default compilation options, but
are not emitted by the compiler with the current default compilation
options.

- tools/bpf/resolve_btfids/main.c: Initialize the variables 'set' and
  'set8' in sets_patch to NULL.

- tools/lib/bpf/btf_dump.c: Initialize the variables 'new_off' and
  'pad_bits' and 'pad_type' in btf_dump_emit_bit_padding to zero/NULL

- tools/lib/subcmd/parse-options.c: Initialize the variable 'o' in
  options__order to NULL.
  Sam James mentioned that Michael Weiß had previously sent an alternative
  patch as
  https://lore.kernel.org/all/20240731085217.94928-1-michael.weiss@aisec.fraunhofer.de/

Tested on x86_64 with clang version 17.0.6 and gcc (GCC) 13.3.1.

  $ for c in gcc clang; do for o in fast g s z $(seq 0 3); do make -C \
  tools/bpf/resolve_btfids/ HOST_CC=${c} "HOSTCFLAGS=-O${o} -Wall" \
  clean all 2>&1 | tee ${c}-O${o}.out; done; done && \
  grep 'warning:\|error:' *.out

  [...]
  clang-O1.out:main.c:163:9: warning: ‘set8’ may be used uninitialized [-Wmaybe-uninitialized]
  clang-O1.out:main.c:163:9: warning: ‘set’ may be used uninitialized [-Wmaybe-uninitialized]
  clang-O2.out:main.c:163:9: warning: ‘set8’ may be used uninitialized [-Wmaybe-uninitialized]
  clang-O2.out:main.c:163:9: warning: ‘set’ may be used uninitialized [-Wmaybe-uninitialized]
  clang-O3.out:main.c:163:9: warning: ‘set8’ may be used uninitialized [-Wmaybe-uninitialized]
  clang-O3.out:main.c:163:9: warning: ‘set’ may be used uninitialized [-Wmaybe-uninitialized]
  clang-Ofast.out:main.c:163:9: warning: ‘set8’ may be used uninitialized [-Wmaybe-uninitialized]
  clang-Ofast.out:main.c:163:9: warning: ‘set’ may be used uninitialized [-Wmaybe-uninitialized]
  clang-Og.out:btf_dump.c:903:42: error: ‘new_off’ may be used uninitialized [-Werror=maybe-uninitialized]
  clang-Og.out:btf_dump.c:917:25: error: ‘pad_type’ may be used uninitialized [-Werror=maybe-uninitialized]
  clang-Og.out:btf_dump.c:930:20: error: ‘pad_bits’ may be used uninitialized [-Werror=maybe-uninitialized]
  clang-Os.out:parse-options.c:832:9: error: ‘o’ may be used uninitialized [-Werror=maybe-uninitialized]
  clang-Oz.out:parse-options.c:832:9: error: ‘o’ may be used uninitialized [-Werror=maybe-uninitialized]
  gcc-O1.out:main.c:163:9: warning: ‘set8’ may be used uninitialized [-Wmaybe-uninitialized]
  gcc-O1.out:main.c:163:9: warning: ‘set’ may be used uninitialized [-Wmaybe-uninitialized]
  gcc-O2.out:main.c:163:9: warning: ‘set8’ may be used uninitialized [-Wmaybe-uninitialized]
  gcc-O2.out:main.c:163:9: warning: ‘set’ may be used uninitialized [-Wmaybe-uninitialized]
  gcc-O3.out:main.c:163:9: warning: ‘set8’ may be used uninitialized [-Wmaybe-uninitialized]
  gcc-O3.out:main.c:163:9: warning: ‘set’ may be used uninitialized [-Wmaybe-uninitialized]
  gcc-Ofast.out:main.c:163:9: warning: ‘set8’ may be used uninitialized [-Wmaybe-uninitialized]
  gcc-Ofast.out:main.c:163:9: warning: ‘set’ may be used uninitialized [-Wmaybe-uninitialized]
  gcc-Og.out:btf_dump.c:903:42: error: ‘new_off’ may be used uninitialized [-Werror=maybe-uninitialized]
  gcc-Og.out:btf_dump.c:917:25: error: ‘pad_type’ may be used uninitialized [-Werror=maybe-uninitialized]
  gcc-Og.out:btf_dump.c:930:20: error: ‘pad_bits’ may be used uninitialized [-Werror=maybe-uninitialized]
  gcc-Os.out:parse-options.c:832:9: error: ‘o’ may be used uninitialized [-Werror=maybe-uninitialized]
  gcc-Oz.out:parse-options.c:832:9: error: ‘o’ may be used uninitialized [-Werror=maybe-uninitialized]

The above warnings and/or errors are fixed. However, they are observed with
current default compilation options.

Updates since v1:

- Incorporate feedback from reviewers. Add a comment about an alternative
  patch for parse-options.c sent before (based on comments from Sam James.)
  Split in multiple patches creating this series and a typo was fixed
  "Initiazlide" -> "Initialize" (suggested by Viktor Malik). State more
  clearly that the -Wmaybe-uninitialized issues only happen when compiling
  with non-default compilation options (based on comments from Yonghong
  Song.)

Thanks,

Eder Zulian (3):
  resolve_btfids: Fix compiler warnings
  libbpf: Prevent compiler warnings/errors
  libsubcmd: Silence compiler warning

 tools/bpf/resolve_btfids/main.c  | 4 ++--
 tools/lib/bpf/btf_dump.c         | 4 ++--
 tools/lib/subcmd/parse-options.c | 2 +-
 3 files changed, 5 insertions(+), 5 deletions(-)

-- 
2.46.2