Re: [PATCH net] tcp: Fix -Wc23-extensions in tcp_options_write()
From: Palmer Dabbelt
Date: Thu Nov 02 2023 - 16:24:01 EST
On Wed, 01 Nov 2023 18:42:10 PDT (-0700), Palmer Dabbelt wrote:
On Wed, 01 Nov 2023 18:07:23 PDT (-0700), nathan@xxxxxxxxxx wrote:
On Wed, Nov 01, 2023 at 05:41:10PM -0700, Palmer Dabbelt wrote:
On Tue, 31 Oct 2023 13:23:35 PDT (-0700), nathan@xxxxxxxxxx wrote:
> 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@xxxxxxxxxx>
> ---
> 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?
12.1, though I can't get a smaller reproducer so I'm going to roll back
to your change and double-check. Might take a bit...
Looks like there was just some bug in my test scripts and the original
patch wasn't actually picked up for all the configs. It's working now,
so
Reviewed-by: Palmer Dabbelt <palmer@xxxxxxxxxxxx>
Sorry for the confusion!
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.
So I think something like
diff --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