Re: [PATCH net] tcp: Fix -Wc23-extensions in tcp_options_write()
From: Nathan Chancellor <nathan@kernel.org>
Date: 2023-11-02 01:07:31
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linux-patches, lkml, llvm
On Wed, Nov 01, 2023 at 05:41:10PM -0700, Palmer Dabbelt wrote:
On Tue, 31 Oct 2023 13:23:35 PDT (-0700), nathan@kernel.org wrote:quoted
Clang warns (or errors with CONFIG_WERROR=y) when CONFIG_TCP_AO is set: net/ipv4/tcp_output.c:663:2: error: label at end of compound statement is a C23 extension [-Werror,-Wc23-extensions] 663 | } | ^ 1 error generated. On earlier releases (such as clang-11, the current minimum supported version for building the kernel) that do not support C23, this was a hard error unconditionally: net/ipv4/tcp_output.c:663:2: error: expected statement } ^ 1 error generated. Add a semicolon after the label to create an empty statement, which resolves the warning or error for all compilers. Closes: https://github.com/ClangBuiltLinux/linux/issues/1953 Fixes: 1e03d32bea8e ("net/tcp: Add TCP-AO sign to outgoing packets") Signed-off-by: Nathan Chancellor <nathan@kernel.org> --- net/ipv4/tcp_output.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index f558c054cf6e..6064895daece 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c@@ -658,7 +658,7 @@ static void tcp_options_write(struct tcphdr *th, struct tcp_sock *tp, memset(ptr, TCPOPT_NOP, sizeof(*ptr)); ptr++; } -out_ao: +out_ao:; #endif } if (unlikely(opts->mss)) {--- base-commit: 55c900477f5b3897d9038446f72a281cae0efd86 change-id: 20231031-tcp-ao-fix-label-in-compound-statement-warning-ebd6c9978498 Best regards,This gives me a linux/net/ipv4/tcp_output.c:663:2: error: expected statement } on GCC for me.
What GCC version?
I cannot reproduce that error with my patch applied. I tested mainline
at commit deefd5024f07 ("Merge tag 'vfio-v6.7-rc1' of
https://github.com/awilliam/linux-vfio") using GCC 6 from kernel.org and
I can reproduce a similar failure with ARCH=x86_64 allyesconfig:
net/ipv4/tcp_output.c: In function 'tcp_options_write':
net/ipv4/tcp_output.c:661:1: error: label at end of compound statement
out_ao:
^~~~~~
With this change applied, the error disappears for GCC 6 and GCC 13
continues to build without error. I can try the other supported versions
later, I just did an older and newer one for a quick test.
quoted hunk ↗ jump to hunk
So I think something likediff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index f558c054cf6e..ca09763acaa8 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c@@ -659,6 +659,11 @@ static void tcp_options_write(struct tcphdr *th, struct tcp_sock *tp,ptr++; } out_ao: + /* + * Labels at the end of compound statements are a C23 feature, so + * introduce a block to avoid a warning/error on strict toolchains. + */ + {} #endif } if (unlikely(opts->mss)) { should do it (though it's still build testing...)
I am not opposed to this once we understand what versions are affected by this so that we have some timeline of removing this workaround. Cheers, Nathan