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Message-ID: <20231102010723.GA406542@dev-arch.thelio-3990X> Date: Wed, 1 Nov 2023 18:07:23 -0700 From: Nathan Chancellor <nathan@...nel.org> To: Palmer Dabbelt <palmer@...belt.com> 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, 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? 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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