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[bpf-next] bpf: build type-punning BPF selftests with -fno-strict-aliasing

Message ID 20240130110343.11217-1-jose.marchesi@oracle.com (mailing list archive)
State Accepted
Commit 27a90b14b93d3b2e1efd10764e456af7e2a42991
Delegated to: BPF
Headers show
Series [bpf-next] bpf: build type-punning BPF selftests with -fno-strict-aliasing | expand

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netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 8 this patch: 8
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netdev/check_selftest success No net selftest shell script
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Commit Message

Jose E. Marchesi Jan. 30, 2024, 11:03 a.m. UTC 
A few BPF selftests perform type punning and they may break strict
aliasing rules, which are exploited by both GCC and clang by default
while optimizing.  This can lead to broken compiled programs.

This patch disables strict aliasing for these particular tests, by
mean of the -fno-strict-aliasing command line option.  This will make
sure these tests are optimized properly even if some strict aliasing
rule gets violated.

After this patch, GCC is able to build all the selftests without
warning about potential strict aliasing issue.

bpf@vger discussion on strict aliasing and BPF selftests:
https://lore.kernel.org/bpf/bae1205a-b6e5-4e46-8e20-520d7c327f7a@linux.dev/T/#t

Tested in bpf-next master.
No regressions.

Signed-off-by: Jose E. Marchesi <jose.marchesi@oracle.com>
Cc: Yonghong Song <yhs@meta.com>
Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: david.faust@oracle.com
Cc: cupertino.miranda@oracle.com
---
 tools/testing/selftests/bpf/Makefile | 13 +++++++++++++
 1 file changed, 13 insertions(+)

Comments

patchwork-bot+netdevbpf@kernel.org Jan. 30, 2024, 3:20 p.m. UTC | #1 
Hello:

This patch was applied to bpf/bpf-next.git (master)
by Daniel Borkmann <daniel@iogearbox.net>:

On Tue, 30 Jan 2024 12:03:43 +0100 you wrote:
> A few BPF selftests perform type punning and they may break strict
> aliasing rules, which are exploited by both GCC and clang by default
> while optimizing.  This can lead to broken compiled programs.
> 
> This patch disables strict aliasing for these particular tests, by
> mean of the -fno-strict-aliasing command line option.  This will make
> sure these tests are optimized properly even if some strict aliasing
> rule gets violated.
> 
> [...]

Here is the summary with links:
  - [bpf-next] bpf: build type-punning BPF selftests with -fno-strict-aliasing
    https://git.kernel.org/bpf/bpf-next/c/27a90b14b93d

You are awesome, thank you!
diff mbox series

Patch

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 1a3654bcb5dd..79253a376fc8 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -41,6 +41,19 @@  CFLAGS += -g $(OPT_FLAGS) -rdynamic					\
 LDFLAGS += $(SAN_LDFLAGS)
 LDLIBS += $(LIBELF_LIBS) -lz -lrt -lpthread
 
+# The following tests perform type punning and they may break strict
+# aliasing rules, which are exploited by both GCC and clang by default
+# while optimizing.  This can lead to broken programs.
+progs/bind4_prog.c-CFLAGS := -fno-strict-aliasing
+progs/bind6_prog.c-CFLAGS := -fno-strict-aliasing
+progs/dynptr_fail.c-CFLAGS := -fno-strict-aliasing
+progs/linked_list_fail.c-CFLAGS := -fno-strict-aliasing
+progs/map_kptr_fail.c-CFLAGS := -fno-strict-aliasing
+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
+
 ifneq ($(LLVM),)
 # Silence some warnings when compiled with clang
 CFLAGS += -Wno-unused-command-line-argument