support linux kernel apis (new archs) with old syscalls removed

such archs are expected to omit definitions of the SYS_* macros for
syscalls their kernels lack from arch/$ARCH/bits/syscall.h. the
preprocessor is then able to select the an appropriate implementation
for affected functions. two basic strategies are used on a
case-by-case basis:

where the old syscalls correspond to deprecated library-level
functions, the deprecated functions have been converted to wrappers
for the modern function, and the modern function has fallback code
(omitted at the preprocessor level on new archs) to make use of the
old syscalls if the new syscall fails with ENOSYS. this also improves
functionality on older kernels and eliminates the incentive to program
with deprecated library-level functions for the sake of compatibility
with older kernels.

in other situations where the old syscalls correspond to library-level
functions which are not deprecated but merely lack some new features,
such as the *at functions, the old syscalls are still used on archs
which support them. this may change at some point in the future if or
when fallback code is added to the new functions to make them usable
(possibly with reduced functionality) on old kernels.

src/linux/epoll.c

@@ -4,12 +4,16 @@
 
 int epoll_create(int size)
 {
-	return syscall(SYS_epoll_create, size);
+	return epoll_create1(0);
 }
 
 int epoll_create1(int flags)
 {
-	return syscall(SYS_epoll_create1, flags);
+	int r = __syscall(SYS_epoll_create1, flags);
+#ifdef SYS_epoll_create
+	if (r==-ENOSYS && !flags) r = __syscall(SYS_epoll_create, 1);
+#endif
+	return __syscall_ret(r);
 }
 
 int epoll_ctl(int fd, int op, int fd2, struct epoll_event *ev)
@@ -19,10 +23,14 @@ int epoll_ctl(int fd, int op, int fd2, struct epoll_event *ev)
 
 int epoll_pwait(int fd, struct epoll_event *ev, int cnt, int to, const sigset_t *sigs)
 {
-	return syscall(SYS_epoll_pwait, fd, ev, cnt, to, sigs, _NSIG/8);
+	int r = __syscall(SYS_epoll_pwait, fd, ev, cnt, to, sigs, _NSIG/8);
+#ifdef SYS_epoll_wait
+	if (r==-ENOSYS && !sigs) r = __syscall(SYS_epoll_wait, fd, ev, cnt, to);
+#endif
+	return __syscall_ret(r);
 }
 
 int epoll_wait(int fd, struct epoll_event *ev, int cnt, int to)
 {
-	return syscall(SYS_epoll_wait, fd, ev, cnt, to);
+	return epoll_pwait(fd, ev, cnt, to, 0);
 }

src/linux/eventfd.c

@@ -4,7 +4,11 @@
 
 int eventfd(unsigned int count, int flags)
 {
-	return syscall(flags ? SYS_eventfd2 : SYS_eventfd, count, flags);
+	int r = __syscall(SYS_eventfd2, count, flags);
+#ifdef SYS_eventfd
+	if (r==-ENOSYS && !flags) r = __syscall(SYS_eventfd, count);
+#endif
+	return __syscall_ret(r);
 }
 
 int eventfd_read(int fd, eventfd_t *value)

src/linux/inotify.c

@@ -3,11 +3,15 @@
 
 int inotify_init()
 {
-	return syscall(SYS_inotify_init);
+	return inotify_init1(0);
 }
 int inotify_init1(int flags)
 {
-	return syscall(SYS_inotify_init1, flags);
+	int r = __syscall(SYS_inotify_init1, flags);
+#ifdef SYS_inotify_init
+	if (r==-ENOSYS && !flags) r = __syscall(SYS_inotify_init);
+#endif
+	return __syscall_ret(r);
 }
 
 int inotify_add_watch(int fd, const char *pathname, uint32_t mask)

src/linux/signalfd.c

@@ -7,6 +7,7 @@
 int signalfd(int fd, const sigset_t *sigs, int flags)
 {
 	int ret = __syscall(SYS_signalfd4, fd, sigs, _NSIG/8, flags);
+#ifdef SYS_signalfd
 	if (ret != -ENOSYS) return __syscall_ret(ret);
 	ret = __syscall(SYS_signalfd, fd, sigs, _NSIG/8);
 	if (ret >= 0) {
@@ -15,5 +16,6 @@ int signalfd(int fd, const sigset_t *sigs, int flags)
 		if (flags & SFD_NONBLOCK)
 			__syscall(SYS_fcntl, ret, F_SETFL, O_NONBLOCK);
 	}
+#endif
 	return __syscall_ret(ret);
 }

src/linux/utimes.c

@@ -1,7 +1,10 @@
 #include <sys/time.h>
+#include "fcntl.h"
 #include "syscall.h"
 
+int __futimesat(int, const char *, const struct timeval [2]);
+
 int utimes(const char *path, const struct timeval times[2])
 {
-	return syscall(SYS_utimes, path, times);
+	return __futimesat(AT_FDCWD, path, times);
 }