Building with Clang 16 fails with sign-compare #936
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A long known issue between musl libc and clang. One way to workaround this would be to create our own wrapper around CMSG_NXTHDR and do the #pragma thing... Something like the following perhaps... diff --git a/src/nxt_socket_msg.h b/src/nxt_socket_msg.h
index 04de1761..fca82f05 100644
--- a/src/nxt_socket_msg.h
+++ b/src/nxt_socket_msg.h
@@ -69,6 +69,19 @@ NXT_EXPORT ssize_t nxt_recvmsg(nxt_socket_t s,
nxt_iobuf_t *iob, nxt_uint_t niob, nxt_recv_oob_t *oob);
+static inline struct cmsghdr *
+NXT_CMSG_NXTHDR(struct msghdr *msg, struct cmsghdr *cmsg)
+{
+#ifndef __GLIBC__
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wsign-compare"
+#endif
+ return CMSG_NXTHDR(msg, cmsg);
+#ifndef __GLIBC__
+#pragma clang diagnostic pop
+#endif
+}
+
nxt_inline void
nxt_socket_msg_oob_init(nxt_send_oob_t *oob, int *fds)
{
@@ -135,7 +148,7 @@ nxt_socket_msg_oob_get_fds(nxt_recv_oob_t *oob, nxt_fd_t *fd
)
for (cmsg = CMSG_FIRSTHDR(&msg);
cmsg != NULL;
- cmsg = CMSG_NXTHDR(&msg, cmsg))
+ cmsg = NXT_CMSG_NXTHDR(&msg, cmsg))
{
size = cmsg->cmsg_len - CMSG_LEN(0);
@@ -174,7 +187,7 @@ nxt_socket_msg_oob_get(nxt_recv_oob_t *oob, nxt_fd_t *fd, nx
t_pid_t *pid)
for (cmsg = CMSG_FIRSTHDR(&msg);
cmsg != NULL;
- cmsg = CMSG_NXTHDR(&msg, cmsg))
+ cmsg = NXT_CMSG_NXTHDR(&msg, cmsg))
{
size = cmsg->cmsg_len - CMSG_LEN(0);
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ac000
added a commit
to ac000/unit
that referenced
this issue
Sep 6, 2023
As reported by @andypost on GitHub, if you try to build Unit on a system that uses musl libc (such as Alpine Linux) with clang then you get the following clang -c -pipe -fPIC -fvisibility=hidden -O -W -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -fstrict-aliasing -Wstrict-overflow=5 -Wmissing-prototypes -Werror -g -I src -I build/include \ \ \ -o build/src/nxt_socketpair.o \ -MMD -MF build/src/nxt_socketpair.dep -MT build/src/nxt_socketpair.o \ src/nxt_socketpair.c In file included from src/nxt_socketpair.c:8: src/nxt_socket_msg.h:138:17: error: comparison of integers of different signs: 'unsigned long' and 'long' [-Werror,-Wsign-compare] cmsg = CMSG_NXTHDR(&msg, cmsg)) ^~~~~~~~~~~~~~~~~~~~~~~ /usr/include/sys/socket.h:358:44: note: expanded from macro 'CMSG_NXTHDR' __CMSG_LEN(cmsg) + sizeof(struct cmsghdr) >= __MHDR_END(mhdr) - (unsigned char *)(cmsg) \ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In file included from src/nxt_socketpair.c:8: src/nxt_socket_msg.h:177:17: error: comparison of integers of different signs: 'unsigned long' and 'long' [-Werror,-Wsign-compare] cmsg = CMSG_NXTHDR(&msg, cmsg)) ^~~~~~~~~~~~~~~~~~~~~~~ /usr/include/sys/socket.h:358:44: note: expanded from macro 'CMSG_NXTHDR' __CMSG_LEN(cmsg) + sizeof(struct cmsghdr) >= __MHDR_END(mhdr) - (unsigned char *)(cmsg) \ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 2 errors generated. make: *** [build/Makefile:261: build/src/nxt_socketpair.o] Error 1 GCC works fine, it seems to have some smarts so that it doesn't give warnings on system header files. This seems to be a long standing issue with musl libc (bad casting in the CMSG_NXTHDR macro) and the workaround employed by several projects is to disable the -Wsign-compare clang warning for the code in question. So, that's what we do. We wrap the CMSG_NXTHDR macro in a function, so we can use the pre-processor in it to selectively disable the warning. Link: <dotnet/runtime#16438> Link: <https://git.openembedded.org/meta-openembedded/tree/meta-oe/recipes-devtools/breakpad/breakpad/0001-Turn-off-sign-compare-for-musl-libc.patch> Link: <https://github.com/dotnet/corefx/blob/57ff88bb75a0/src/Native/Unix/System.Native/pal_networking.c#L811-L829> Link: <https://patchwork.yoctoproject.org/project/oe/patch/20220407191438.3696227-1-stefan@datenfreihafen.org/> Closes: <nginx#936> Signed-off-by: Andrew Clayton <a.clayton@nginx.com>
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Hi, @ac000 @andypost @andrey-zelenkov Do we need to add it to BB? |
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nginx has the same issue |
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Good catch, thanks. |
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See https://trac.nginx.org/nginx/ticket/2534 for the related issue in nginx. They decided not to fix that. |
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That's their perogative. I don't see a compelling reason why we shouldn't. |
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@ac000 thank you for patch! it allows to build meantime exposed issues on armv7 and armv8 and riscv64 maybe it's related to clang for this arches but at least "GCC" prefix for atomics is confusing when building with clang |
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Using clang 15.0.7 I'm getting the same error |
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Thanks for testing.
Hmm, we just have the three above checks here, one for GCC 4.1+ (heh, I'm just quoting the auto/atomic script), Solaris 10 & AIX xlC. The mind boggles, I suspect these just came straight from nginx... It's also weird that it failed to find all the builtins and attributes... I assume GCC builds Unit fine on such systems? Some more investigation is probably required... |
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Yes, using GCC it builds/works fine, I just attempted to use clang to see effect |
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Thanks for confirming. No, sure, while GCC is my compiler of choice I see value in also testing with clang, they both find different issues in code. |
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Lets move this to a separate issue... |
ac000
added a commit
to ac000/unit
that referenced
this issue
Sep 11, 2023
As reported by @andypost on GitHub, if you try to build Unit on a system that uses musl libc (such as Alpine Linux) with clang then you get the following clang -c -pipe -fPIC -fvisibility=hidden -O -W -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -fstrict-aliasing -Wstrict-overflow=5 -Wmissing-prototypes -Werror -g -I src -I build/include \ \ \ -o build/src/nxt_socketpair.o \ -MMD -MF build/src/nxt_socketpair.dep -MT build/src/nxt_socketpair.o \ src/nxt_socketpair.c In file included from src/nxt_socketpair.c:8: src/nxt_socket_msg.h:138:17: error: comparison of integers of different signs: 'unsigned long' and 'long' [-Werror,-Wsign-compare] cmsg = CMSG_NXTHDR(&msg, cmsg)) ^~~~~~~~~~~~~~~~~~~~~~~ /usr/include/sys/socket.h:358:44: note: expanded from macro 'CMSG_NXTHDR' __CMSG_LEN(cmsg) + sizeof(struct cmsghdr) >= __MHDR_END(mhdr) - (unsigned char *)(cmsg) \ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In file included from src/nxt_socketpair.c:8: src/nxt_socket_msg.h:177:17: error: comparison of integers of different signs: 'unsigned long' and 'long' [-Werror,-Wsign-compare] cmsg = CMSG_NXTHDR(&msg, cmsg)) ^~~~~~~~~~~~~~~~~~~~~~~ /usr/include/sys/socket.h:358:44: note: expanded from macro 'CMSG_NXTHDR' __CMSG_LEN(cmsg) + sizeof(struct cmsghdr) >= __MHDR_END(mhdr) - (unsigned char *)(cmsg) \ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 2 errors generated. make: *** [build/Makefile:261: build/src/nxt_socketpair.o] Error 1 GCC works fine, it seems to have some smarts so that it doesn't give warnings on system header files. This seems to be a long standing issue with musl libc (bad casting in the CMSG_NXTHDR macro) and the workaround employed by several projects is to disable the -Wsign-compare clang warning for the code in question. So, that's what we do. We wrap the CMSG_NXTHDR macro in a function, so we can use the pre-processor in it to selectively disable the warning. Link: <dotnet/runtime#16438> Link: <https://git.openembedded.org/meta-openembedded/tree/meta-oe/recipes-devtools/breakpad/breakpad/0001-Turn-off-sign-compare-for-musl-libc.patch> Link: <https://github.com/dotnet/corefx/blob/57ff88bb75a0/src/Native/Unix/System.Native/pal_networking.c#L811-L829> Link: <https://patchwork.yoctoproject.org/project/oe/patch/20220407191438.3696227-1-stefan@datenfreihafen.org/> Closes: <nginx#936> Signed-off-by: Andrew Clayton <a.clayton@nginx.com>
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Fix was committed. |
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Trying to build for Alpinelinux using Clang
--cc=clangbut getting error and the only workaround is to use--cc-opt="$CFLAGS -Eno-sign-compare"The text was updated successfully, but these errors were encountered: