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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 '<cerrno>'; did you forget to '#include <cerrno>'? 23 | #include <unistd.h> +++ |+#include <cerrno> 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 <bees@furryterror.org>
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@@ -4,9 +4,7 @@
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// Compatibility for building on old libc for new kernel
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#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 6, 0)
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// Every arch that defines this uses 437, except Alpha, where 437 is
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// Every arch that defines this (so far) uses 437, except Alpha, where 437 is
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// mq_getsetattr.
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#ifndef SYS_openat2
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@@ -17,8 +15,6 @@
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#endif
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#endif
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#endif // Linux version >= v5.6
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#include <fcntl.h>
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#include <unistd.h>
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@@ -29,12 +25,7 @@ __attribute__((weak))
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openat2(int const dirfd, const char *const pathname, struct open_how *const how, size_t const size)
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throw()
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{
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#ifdef SYS_openat2
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return syscall(SYS_openat2, dirfd, pathname, how, size);
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#else
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errno = ENOSYS;
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return -1;
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#endif
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}
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};
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