diff options
| author | Jose E. Marchesi <jose.marchesi@oracle.com> | 2024-05-12 00:22:13 +0300 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2024-05-13 03:30:15 +0300 |
| commit | 73868988c90d2701587ab2a48b5858ab935afb17 (patch) | |
| tree | 651bdcfb5aa1713c2a6acc32ff271dab95d8bc85 /tools | |
| parent | a3c1c95538e22283ef6fa529e3ffa0e6d47ee190 (diff) | |
| download | linux-73868988c90d2701587ab2a48b5858ab935afb17.tar.xz | |
bpf: disable strict aliasing in test_global_func9.c
The BPF selftest test_global_func9.c performs type punning and breaks
srict-aliasing rules.
In particular, given:
int global_func9(struct __sk_buff *skb)
{
int result = 0;
[...]
{
const struct C c = {.x = skb->len, .y = skb->family };
result |= foo((const struct S *)&c);
}
}
When building with strict-aliasing enabled (the default) the
initialization of `c' gets optimized away in its entirely:
[... no initialization of `c' ...]
r1 = r10
r1 += -40
call foo
w0 |= w6
Since GCC knows that `foo' accesses s->x, we get a "maybe
uninitialized" warning.
On the other hand, when strict-aliasing is disabled GCC only optimizes
away the store to `.y':
r1 = *(u32 *) (r6+0)
*(u32 *) (r10+-40) = r1 ; This is .x = skb->len in `c'
r1 = r10
r1 += -40
call foo
w0 |= w6
In this case the warning is not emitted, because s-> is initialized.
This patch disables strict aliasing in this test when building with
GCC. clang seems to not optimize this particular code even when
strict aliasing is enabled.
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>
Link: https://lore.kernel.org/r/20240511212213.23418-1-jose.marchesi@oracle.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'tools')
| -rw-r--r-- | tools/testing/selftests/bpf/Makefile | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile index ed381b0197fe..e0b3887b3d2d 100644 --- a/tools/testing/selftests/bpf/Makefile +++ b/tools/testing/selftests/bpf/Makefile @@ -53,6 +53,7 @@ progs/syscall.c-CFLAGS := -fno-strict-aliasing progs/test_pkt_md_access.c-CFLAGS := -fno-strict-aliasing progs/test_sk_lookup.c-CFLAGS := -fno-strict-aliasing progs/timer_crash.c-CFLAGS := -fno-strict-aliasing +progs/test_global_func9.c-CFLAGS := -fno-strict-aliasing ifneq ($(LLVM),) # Silence some warnings when compiled with clang |