From: "Jose E. Marchesi" <jose.marchesi@oracle.com>
To: bpf@vger.kernel.org
Cc: "Jose E . Marchesi" <jose.marchesi@oracle.com>,
david.faust@oracle.com, cupertino.miranda@oracle.com,
Yonghong Song <yonghong.song@linux.dev>,
Eduard Zingerman <eddyz87@gmail.com>
Subject: [PATCH bpf-next] bpf: disable some `attribute ignored' warnings in GCC
Date: Fri, 3 May 2024 14:32:13 +0200 [thread overview]
Message-ID: <20240503123213.5380-1-jose.marchesi@oracle.com> (raw)
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 bening.
- visibility
In progs/cpumask_common.h:13 there is:
#define private(name) SEC(".bss." #name) __hidden __attribute__((aligned(8)))
private(MASK) static struct bpf_cpumask __kptr * global_mask;
The __hidden macro defines to:
tools/lib/bpf/bpf_helpers.h:#define __hidden __attribute__((visibility("hidden")))
GCC emits an "attribute ignored" warning because static implies
hidden visibility.
Ignoring this warning is benign. An alternative would be to make
global_mask as non-static.
- 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 bening, 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 pehaps 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@oracle.com>
Cc: david.faust@oracle.com
Cc: cupertino.miranda@oracle.com
Cc: Yonghong Song <yonghong.song@linux.dev>
Cc: Eduard Zingerman <eddyz87@gmail.com>
---
tools/testing/selftests/bpf/Makefile | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index ba28d42b74db..5d9c906bc3cb 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -431,7 +431,7 @@ 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
--
2.30.2
next reply other threads:[~2024-05-03 12:32 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-03 12:32 Jose E. Marchesi [this message]
2024-05-06 18:32 ` [PATCH bpf-next] bpf: disable some `attribute ignored' warnings in GCC Yonghong Song
2024-05-06 19:09 ` David Faust
2024-05-06 21:42 ` Yonghong Song
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