From e852e3998aa7be699ce5231cea16632aafca78ca Mon Sep 17 00:00:00 2001 From: Zygo Blaxell Date: Mon, 7 Jul 2025 14:27:57 -0400 Subject: [PATCH] openat2: LINUX_VERSION_CODE is defined by linux-libc-dev, not libc With new kernel headers and old libc, `SYS_openat2` can still end up undefined, which triggers the fallback build-time code, that doesn't build: ``` openat2.cc: In function 'int openat2(int, const char*, open_how*, size_t)': openat2.cc:35:2: error: 'errno' was not declared in this scope 35 | errno = ENOSYS; | ^~~~~ openat2.cc:24:1: note: 'errno' is defined in header ''; did you forget to '#include '? 23 | #include +++ |+#include 24 | openat2.cc:35:10: error: 'ENOSYS' was not declared in this scope 35 | errno = ENOSYS; | ^~~~~~ openat2.cc:29:19: error: unused parameter 'dirfd' [-Werror=unused-parameter] 29 | openat2(int const dirfd, const char *const pathname, struct open_how *const how, size_t const size) | ~~~~~~~~~~^~~~~ openat2.cc:29:44: error: unused parameter 'pathname' [-Werror=unused-parameter] 29 | openat2(int const dirfd, const char *const pathname, struct open_how *const how, size_t const size) | ~~~~~~~~~~~~~~~~~~^~~~~~~~ openat2.cc:29:77: error: unused parameter 'how' [-Werror=unused-parameter] 29 | t dirfd, const char *const pathname, struct open_how *const how, size_t const size) | ~~~~~~~~~~~~~~~~~~~~~~~^~~ openat2.cc:29:95: error: unused parameter 'size' [-Werror=unused-parameter] 29 | st char *const pathname, struct open_how *const how, size_t const size) | ~~~~~~~~~~~~~^~~~ ``` Skip the kernel version check and test for the definition of `SYS_openat2` directly. If it's not there, plug in the constant so we can send the call directly to the kernel, bypassing libc completely. Fixes: https://github.com/Zygo/bees/issues/318 Signed-off-by: Zygo Blaxell --- lib/openat2.cc | 11 +---------- 1 file changed, 1 insertion(+), 10 deletions(-) diff --git a/lib/openat2.cc b/lib/openat2.cc index d868234..5b76bb0 100644 --- a/lib/openat2.cc +++ b/lib/openat2.cc @@ -4,9 +4,7 @@ // Compatibility for building on old libc for new kernel -#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 6, 0) - -// Every arch that defines this uses 437, except Alpha, where 437 is +// Every arch that defines this (so far) uses 437, except Alpha, where 437 is // mq_getsetattr. #ifndef SYS_openat2 @@ -17,8 +15,6 @@ #endif #endif -#endif // Linux version >= v5.6 - #include #include @@ -29,12 +25,7 @@ __attribute__((weak)) openat2(int const dirfd, const char *const pathname, struct open_how *const how, size_t const size) throw() { -#ifdef SYS_openat2 return syscall(SYS_openat2, dirfd, pathname, how, size); -#else - errno = ENOSYS; - return -1; -#endif } };