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Message-ID: <mhng-41e9fb36-f703-461e-b585-9e8dd5984714@palmer-ri-x1c9a> Date: Wed, 01 Nov 2023 18:42:10 -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 18:07:23 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... > 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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