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e852e3998a
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>
32 lines
572 B
C++
32 lines
572 B
C++
#include "crucible/openat2.h"
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#include <sys/syscall.h>
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// Compatibility for building on old libc for new kernel
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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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#ifdef __alpha__
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#define SYS_openat2 547
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#else
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#define SYS_openat2 437
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#endif
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#endif
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#include <fcntl.h>
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#include <unistd.h>
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extern "C" {
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int
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__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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return syscall(SYS_openat2, dirfd, pathname, how, size);
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}
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};
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