[PATCH] bpf: fix constraint in test_tcpbpf_kern.c

[PATCH] bpf: fix constraint in test_tcpbpf_kern.c

[Jose E. Marchesi]

GCC emits a warning:

  progs/test_tcpbpf_kern.c:60:9: error: ‘op’ is used uninitialized [-Werror=uninitialized]

when an uninialized op is used iwth a "+r" constraint.  The + modifier
means a read-write operand, but that operand in the selftest is just
written to.

This patch changes the selftest to use a "=r" constraint.  This
pacifies GCC.

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/progs/test_tcpbpf_kern.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/progs/test_tcpbpf_kern.c b/tools/testing/selftests/bpf/progs/test_tcpbpf_kern.c
index cf7ed8cbb1fe..a3f3f43fc195 100644
--- a/tools/testing/selftests/bpf/progs/test_tcpbpf_kern.c
+++ b/tools/testing/selftests/bpf/progs/test_tcpbpf_kern.c
@@ -59,7 +59,7 @@ int bpf_testcb(struct bpf_sock_ops *skops)
 
 	asm volatile (
 		"%[op] = *(u32 *)(%[skops] +96)"
-		: [op] "+r"(op)
+		: [op] "=r"(op)
 		: [skops] "r"(skops)
 		:);
 
-- 
2.30.2

Re: [PATCH] bpf: fix constraint in test_tcpbpf_kern.c

[Yonghong Song]

On 1/23/24 12:56 PM, Jose E. Marchesi wrote:
> GCC emits a warning:
>
>    progs/test_tcpbpf_kern.c:60:9: error: ‘op’ is used uninitialized [-Werror=uninitialized]
>
> when an uninialized op is used iwth a "+r" constraint.  The + modifier
iwth -> with
> means a read-write operand, but that operand in the selftest is just
> written to.
>
> This patch changes the selftest to use a "=r" constraint.  This
> pacifies GCC.
>
> 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

Acked-by: Yonghong Song <yonghong.song@linux.dev>

Re: [PATCH] bpf: fix constraint in test_tcpbpf_kern.c

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <ast@kernel.org>:

On Tue, 23 Jan 2024 21:56:24 +0100 you wrote:
> GCC emits a warning:
> 
>   progs/test_tcpbpf_kern.c:60:9: error: ‘op’ is used uninitialized [-Werror=uninitialized]
> 
> when an uninialized op is used iwth a "+r" constraint.  The + modifier
> means a read-write operand, but that operand in the selftest is just
> written to.
> 
> [...]

Here is the summary with links:
  - bpf: fix constraint in test_tcpbpf_kern.c
    https://git.kernel.org/bpf/bpf-next/c/756e34da5380

You are awesome, thank you!
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