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Message-ID: <mhng-7500e386-1e83-4303-a1ee-cd2d5688e73e@palmer-ri-x1c9> Date: Thu, 02 Nov 2023 13:23:54 -0700 (PDT) From: Palmer Dabbelt <palmer@...belt.com> To: nathan@...nel.org CC: edumazet@...gle.com, davem@...emloft.net, dsahern@...nel.org, kuba@...nel.org, pabeni@...hat.com, ndesaulniers@...gle.com, trix@...hat.com, 0x7f454c46@...il.com, fruggeri@...sta.com, noureddine@...sta.com, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, llvm@...ts.linux.dev, patches@...ts.linux.dev Subject: Re: [PATCH net] tcp: Fix -Wc23-extensions in tcp_options_write() On Wed, 01 Nov 2023 18:42:10 PDT (-0700), Palmer Dabbelt wrote: > On Wed, 01 Nov 2023 18:07:23 PDT (-0700), nathan@...nel.org 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@...nel.org 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@...nel.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? > > 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@...osinc.com> 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
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