This is a note to let you know that I've just added the patch titled
bpf: Disable some `attribute ignored' warnings in GCC
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
bpf-disable-some-attribute-ignored-warnings-in-gcc.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 769f04a675da33fdcebff9296b35e1b98ddd4861
Author: Jose E. Marchesi <jose.marchesi@xxxxxxxxxx>
Date: Tue May 7 09:42:27 2024 +0200
bpf: Disable some `attribute ignored' warnings in GCC
[ Upstream commit b0fbdf759da05a35b67fd27b8859738b79af25d6 ]
This patch modifies selftests/bpf/Makefile to pass -Wno-attributes to
GCC. This is because of the following attributes which are ignored:
- btf_decl_tag
- btf_type_tag
There are many of these. At the moment none of these are
recognized/handled by gcc-bpf.
We are aware that btf_decl_tag is necessary for some of the
selftest harness to communicate test failure/success. Support for
it is in progress in GCC upstream:
https://gcc.gnu.org/pipermail/gcc-patches/2024-May/650482.html
However, the GCC master branch is not yet open, so the series
above (currently under review upstream) wont be able to make it
there until 14.1 gets released, probably mid next week.
As for btf_type_tag, more extensive work will be needed in GCC
upstream to support it in both BTF and DWARF. We have a WIP big
patch for that, but that is not needed to compile/build the
selftests.
- used
There are SEC macros defined in the selftests as:
#define SEC(N) __attribute__((section(N),used))
The SEC macro is used for both functions and global variables.
According to the GCC documentation `used' attribute is really only
meaningful for functions, and it warns when the attribute is used
for other global objects, like for example ctl_array in
test_xdp_noinline.c.
Ignoring this is benign.
- align_value
In progs/test_cls_redirect.c:127 there is:
typedef uint8_t *net_ptr __attribute__((align_value(8)));
GCC warns that it is ignoring this attribute, because it is not
implemented by GCC.
I think ignoring this attribute in GCC is benign, because according
to the clang documentation [1] its purpose seems to be merely
declarative and doesn't seem to translate into extra checks at
run-time, only to perhaps better optimized code ("runtime behavior
is undefined if the pointed memory object is not aligned to the
specified alignment").
[1] https://clang.llvm.org/docs/AttributeReference.html#align-value
Tested in bpf-next master.
Signed-off-by: Jose E. Marchesi <jose.marchesi@xxxxxxxxxx>
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Acked-by: Yonghong Song <yonghong.song@xxxxxxxxx>
Link: https://lore.kernel.org/bpf/20240507074227.4523-3-jose.marchesi@xxxxxxxxxx
Stable-dep-of: 3ece93a4087b ("selftests/bpf: Fix wrong binary in Makefile log output")
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 397306f5cf911..e0f499794f162 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -412,7 +412,7 @@ endef
# Build BPF object using GCC
define GCC_BPF_BUILD_RULE
$(call msg,GCC-BPF,$(TRUNNER_BINARY),$2)
- $(Q)$(BPF_GCC) $3 -O2 -c $1 -o $2
+ $(Q)$(BPF_GCC) $3 -Wno-attributes -O2 -c $1 -o $2
endef
SKEL_BLACKLIST := btf__% test_pinning_invalid.c test_sk_assign.c
