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/env/__libc_start_main.c

 #include <elf.h>
 #include <poll.h>
 #include <fcntl.h>
+#include <signal.h>
 #include "syscall.h"
 #include "atomic.h"
 #include "libc.h"
@@ -48,7 +49,11 @@ void __init_libc(char **envp, char *pn)
 		&& !aux[AT_SECURE]) return;
 
 	struct pollfd pfd[3] = { {.fd=0}, {.fd=1}, {.fd=2} };
+#ifdef SYS_poll
 	__syscall(SYS_poll, pfd, 3, 0);
+#else
+	__syscall(SYS_ppoll, pfd, 3, &(struct timespec){0}, 0, _NSIG/8);
+#endif
 	for (i=0; i<3; i++) if (pfd[i].revents&POLLNVAL)
 		if (__sys_open("/dev/null", O_RDWR)<0)
 			a_crash();

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

 #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);
 }

src/process/fork.c

 #include <unistd.h>
 #include <string.h>
+#include <signal.h>
 #include "syscall.h"
 #include "libc.h"
 #include "pthread_impl.h"
@@ -16,7 +17,11 @@ pid_t fork(void)
 	sigset_t set;
 	__fork_handler(-1);
 	__block_all_sigs(&set);
+#ifdef SYS_fork
 	ret = syscall(SYS_fork);
+#else
+	ret = syscall(SYS_clone, SIGCHLD, 0);
+#endif
 	if (libc.has_thread_pointer && !ret) {
 		pthread_t self = __pthread_self();
 		self->tid = self->pid = __syscall(SYS_getpid);

src/process/posix_spawn.c

@@ -22,6 +22,20 @@ struct args {
 
 void __get_handler_set(sigset_t *);
 
+static int __sys_dup2(int old, int new)
+{
+#ifdef SYS_dup2
+	return __syscall(SYS_dup2, old, new);
+#else
+	if (old==new) {
+		int r = __syscall(SYS_fcntl, old, F_GETFD);
+		return r<0 ? r : old;
+	} else {
+		return __syscall(SYS_dup3, old, new, 0);
+	}
+#endif
+}
+
 static int child(void *args_vp)
 {
 	int i, ret;
@@ -92,14 +106,14 @@ static int child(void *args_vp)
 					goto fail;
 				break;
 			case FDOP_DUP2:
-				if ((ret=__syscall(SYS_dup2, op->srcfd, op->fd))<0)
+				if ((ret=__sys_dup2(op->srcfd, op->fd))<0)
 					goto fail;
 				break;
 			case FDOP_OPEN:
 				fd = __sys_open(op->path, op->oflag, op->mode);
 				if ((ret=fd) < 0) goto fail;
 				if (fd != op->fd) {
-					if ((ret=__syscall(SYS_dup2, fd, op->fd))<0)
+					if ((ret=__sys_dup2(fd, op->fd))<0)
 						goto fail;
 					__syscall(SYS_close, fd);
 				}

src/select/poll.c

 #include <poll.h>
+#include <time.h>
+#include <signal.h>
 #include "syscall.h"
 #include "libc.h"
 
 int poll(struct pollfd *fds, nfds_t n, int timeout)
 {
+#ifdef SYS_poll
 	return syscall_cp(SYS_poll, fds, n, timeout);
+#else
+	return syscall_cp(SYS_ppoll, fds, n, timeout>=0 ?
+		&((struct timespec){ .tv_sec = timeout/1000,
+		.tv_nsec = timeout%1000*1000000 }) : 0, 0, _NSIG/8);
+#endif
 }

src/select/select.c

 #include <sys/select.h>
+#include <signal.h>
+#include <stdint.h>
+#include <errno.h>
 #include "syscall.h"
 #include "libc.h"
 
 int select(int n, fd_set *restrict rfds, fd_set *restrict wfds, fd_set *restrict efds, struct timeval *restrict tv)
 {
+#ifdef SYS_select
 	return syscall_cp(SYS_select, n, rfds, wfds, efds, tv);
+#else
+	syscall_arg_t data[2] = { 0, _NSIG/8 };
+	struct timespec ts;
+	if (tv) {
+		if (tv->tv_sec < 0 || tv->tv_usec < 0)
+			return __syscall_ret(-EINVAL);
+		time_t extra_secs = tv->tv_usec / 1000000;
+		ts.tv_nsec = tv->tv_usec % 1000000 * 1000;
+		const time_t max_time = (1ULL<<8*sizeof(time_t)-1)-1;
+		ts.tv_sec = extra_secs > max_time - tv->tv_sec ?
+			max_time : tv->tv_sec + extra_secs;
+	}
+	return syscall_cp(SYS_pselect6, n, rfds, wfds, efds, tv ? &ts : 0, data);
+#endif
 }

src/stat/chmod.c

 #include <sys/stat.h>
+#include <fcntl.h>
 #include "syscall.h"
 
 int chmod(const char *path, mode_t mode)
 {
+#ifdef SYS_chmod
 	return syscall(SYS_chmod, path, mode);
+#else
+	return syscall(SYS_fchmodat, AT_FDCWD, path, mode);
+#endif
 }

src/stat/fchmod.c

@@ -13,5 +13,9 @@ int fchmod(int fd, mode_t mode)
 
 	char buf[15+3*sizeof(int)];
 	__procfdname(buf, fd);
+#ifdef SYS_chmod
 	return syscall(SYS_chmod, buf, mode);
+#else
+	return syscall(SYS_fchmodat, AT_FDCWD, buf, mode);
+#endif
 }

src/stat/fchmodat.c

@@ -28,8 +28,9 @@ int fchmodat(int fd, const char *path, mode_t mode, int flag)
 	}
 
 	__procfdname(proc, fd2);
-	if (!(ret = __syscall(SYS_stat, proc, &st)) && !S_ISLNK(st.st_mode))
-		ret = __syscall(SYS_chmod, proc, mode);
+	ret = __syscall(SYS_fstatat, AT_FDCWD, proc, &st, 0);
+	if (!ret && !S_ISLNK(st.st_mode))
+		ret = __syscall(SYS_fchmodat, AT_FDCWD, proc, mode);
 
 	__syscall(SYS_close, fd2);
 	return __syscall_ret(ret);

src/stat/futimesat.c

 #define _GNU_SOURCE
 #include <sys/time.h>
+#include <sys/stat.h>
+#include <errno.h>
 #include "syscall.h"
+#include "libc.h"
 
-#ifdef SYS_futimesat
-int futimesat(int dirfd, const char *pathname, const struct timeval times[2])
+int __futimesat(int dirfd, const char *pathname, const struct timeval times[2])
 {
-	return syscall(SYS_futimesat, dirfd, pathname, times);
+	struct timespec ts[2];
+	if (times) {
+		int i;
+		for (i=0; i<2; i++) {
+			if (times[i].tv_usec >= 1000000ULL)
+				return __syscall_ret(-EINVAL);
+			ts[i].tv_sec = times[i].tv_sec;
+			ts[i].tv_nsec = times[i].tv_usec * 1000;
+		}
+	}
+	return utimensat(dirfd, pathname, times ? ts : 0, 0);
 }
-#endif
+
+weak_alias(__futimesat, futimesat);

src/stat/lstat.c

 #include <sys/stat.h>
+#include <fcntl.h>
 #include "syscall.h"
 #include "libc.h"
 
 int lstat(const char *restrict path, struct stat *restrict buf)
 {
+#ifdef SYS_lstat
 	return syscall(SYS_lstat, path, buf);
+#else
+	return syscall(SYS_fstatat, AT_FDCWD, path, buf, AT_SYMLINK_NOFOLLOW);
+#endif
 }
 
 LFS64(lstat);

src/stat/mkdir.c

 #include <sys/stat.h>
+#include <fcntl.h>
 #include "syscall.h"
 
 int mkdir(const char *path, mode_t mode)
 {
+#ifdef SYS_mkdir
 	return syscall(SYS_mkdir, path, mode);
+#else
+	return syscall(SYS_mkdirat, AT_FDCWD, path, mode);
+#endif
 }

src/stat/mknod.c

 #include <sys/stat.h>
+#include <fcntl.h>
 #include "syscall.h"
 
 int mknod(const char *path, mode_t mode, dev_t dev)
 {
+#ifdef SYS_mknod
 	return syscall(SYS_mknod, path, mode, dev);
+#else
+	return syscall(SYS_mknodat, AT_FDCWD, path, mode, dev);
+#endif
 }

src/stat/stat.c

 #include <sys/stat.h>
+#include <fcntl.h>
 #include "syscall.h"
 #include "libc.h"
 
 int stat(const char *restrict path, struct stat *restrict buf)
 {
+#ifdef SYS_stat
 	return syscall(SYS_stat, path, buf);
+#else
+	return syscall(SYS_fstatat, AT_FDCWD, path, buf, 0);
+#endif
 }
 
 LFS64(stat);

src/stat/utimensat.c

 #include <sys/stat.h>
+#include <sys/time.h>
+#include <fcntl.h>
+#include <errno.h>
 #include "syscall.h"
 
 int utimensat(int fd, const char *path, const struct timespec times[2], int flags)
 {
-	return syscall(SYS_utimensat, fd, path, times, flags);
+	int r = __syscall(SYS_utimensat, fd, path, times, flags);
+#ifdef SYS_futimesat
+	if (r != -ENOSYS || flags) return __syscall_ret(r);
+	struct timeval *tv = 0, tmp[2];
+	if (times) {
+		int i;
+		tv = tmp;
+		for (i=0; i<2; i++) {
+			if (times[i].tv_nsec >= 1000000000ULL) {
+				if (times[i].tv_nsec == UTIME_NOW &&
+				    times[1-i].tv_nsec == UTIME_NOW) {
+					tv = 0;
+					break;
+				}
+				if (times[i].tv_nsec == UTIME_OMIT)
+					return __syscall_ret(-ENOSYS);
+				return __syscall_ret(-EINVAL);
+			}
+			tmp[i].tv_sec = times[i].tv_sec;
+			tmp[i].tv_usec = times[i].tv_nsec / 1000;
+		}
+	}
+
+	r = __syscall(SYS_futimesat, fd, path, tv);
+	if (r != -ENOSYS || fd != AT_FDCWD) return __syscall_ret(r);
+	r = __syscall(SYS_utimes, path, tv);
+#endif
+	return __syscall_ret(r);
 }

src/stdio/remove.c

 #include <stdio.h>
 #include <errno.h>
+#include <fcntl.h>
 #include "syscall.h"
 
 int remove(const char *path)
 {
-	int r = syscall(SYS_unlink, path);
-	return (r && errno == EISDIR) ? syscall(SYS_rmdir, path) : r;
+#ifdef SYS_unlink
+	int r = __syscall(SYS_unlink, path);
+#else
+	int r = __syscall(SYS_unlinkat, AT_FDCWD, path, 0);
+#endif
+#ifdef SYS_rmdir
+	if (r==-EISDIR) r = __syscall(SYS_rmdir, path);
+#else
+	if (r==-EISDIR) r = __syscall(SYS_unlinkat, AT_FDCWD, path, AT_REMOVEDIR);
+#endif
+	return __syscall_ret(r);
 }

src/stdio/rename.c

 #include <stdio.h>
+#include <fcntl.h>
 #include "syscall.h"
 
 int rename(const char *old, const char *new)
 {
+#ifdef SYS_rename
 	return syscall(SYS_rename, old, new);
+#else
+	return syscall(SYS_renameat, AT_FDCWD, old, AT_FDCWD, new);
+#endif
 }

src/stdio/tempnam.c

@@ -36,7 +36,12 @@ char *tempnam(const char *dir, const char *pfx)
 
 	for (try=0; try<MAXTRIES; try++) {
 		__randname(s+l-6);
+#ifdef SYS_lstat
 		r = __syscall(SYS_lstat, s, &(struct stat){0});
+#else
+		r = __syscall(SYS_fstatat, AT_FDCWD, s,
+			&(struct stat){0}, AT_SYMLINK_NOFOLLOW);
+#endif
 		if (r == -ENOENT) return strdup(s);
 	}
 	return 0;

src/stdio/tmpfile.c

@@ -17,7 +17,11 @@ FILE *tmpfile(void)
 		fd = sys_open(s, O_RDWR|O_CREAT|O_EXCL, 0600);
 		if (fd >= 0) {
 			f = __fdopen(fd, "w+");
+#ifdef SYS_unlink
 			__syscall(SYS_unlink, s);
+#else
+			__syscall(SYS_unlinkat, AT_FDCWD, s, 0);
+#endif
 			return f;
 		}
 	}

src/stdio/tmpnam.c

@@ -17,7 +17,12 @@ char *tmpnam(char *buf)
 	int r;
 	for (try=0; try<MAXTRIES; try++) {
 		__randname(s+12);
+#ifdef SYS_lstat
 		r = __syscall(SYS_lstat, s, &(struct stat){0});
+#else
+		r = __syscall(SYS_fstatat, AT_FDCWD, s,
+			&(struct stat){0}, AT_SYMLINK_NOFOLLOW);
+#endif
 		if (r == -ENOENT) return strcpy(buf ? buf : internal, s);
 	}
 	return 0;

src/time/utime.c

 #include <utime.h>
-#include <sys/time.h>
-#include "syscall.h"
+#include <sys/stat.h>
+#include <time.h>
+#include <fcntl.h>
 
 int utime(const char *path, const struct utimbuf *times)
 {
-	if (times) {
-		struct timeval tv[2] = {
-			{ .tv_sec = times->actime },
-			{ .tv_sec = times->modtime } };
-		return syscall(SYS_utimes, path, tv);
-	}
-	return syscall(SYS_utimes, path, 0);
+	return utimensat(AT_FDCWD, path, times ? ((struct timespec [2]){
+		{ .tv_sec = times->actime }, { .tv_sec = times->modtime }})
+		: 0, 0);
 }

src/unistd/access.c

 #include <unistd.h>
+#include <fcntl.h>
 #include "syscall.h"
 
 int access(const char *filename, int amode)
 {
+#ifdef SYS_access
 	return syscall(SYS_access, filename, amode);
+#else
+	return syscall(SYS_faccessat, AT_FDCWD, filename, amode, 0);
+#endif
 }

src/unistd/chown.c

 #include <unistd.h>
+#include <fcntl.h>
 #include "syscall.h"
 
 int chown(const char *path, uid_t uid, gid_t gid)
 {
+#ifdef SYS_chown
 	return syscall(SYS_chown, path, uid, gid);
+#else
+	return syscall(SYS_fchownat, AT_FDCWD, path, uid, gid, 0);
+#endif
 }

src/unistd/dup2.c

 #include <unistd.h>
 #include <errno.h>
+#include <fcntl.h>
 #include "syscall.h"
 
 int dup2(int old, int new)
 {
 	int r;
+#ifdef SYS_dup2
 	while ((r=__syscall(SYS_dup2, old, new))==-EBUSY);
+#else
+	if (old==new) {
+		r = __syscall(SYS_fcntl, old, F_GETFD);
+		if (r >= 0) return old;
+	} else {
+		while ((r=__syscall(SYS_dup3, old, new, 0))==-EBUSY);
+	}
+#endif
 	return __syscall_ret(r);
 }

src/unistd/dup3.c

@@ -8,6 +8,7 @@
 int __dup3(int old, int new, int flags)
 {
 	int r;
+#ifdef SYS_dup2
 	if (old==new) return __syscall_ret(-EINVAL);
 	if (flags & O_CLOEXEC) {
 		while ((r=__syscall(SYS_dup3, old, new, flags))==-EBUSY);
@@ -15,6 +16,9 @@ int __dup3(int old, int new, int flags)
 	}
 	while ((r=__syscall(SYS_dup2, old, new))==-EBUSY);
 	if (flags & O_CLOEXEC) __syscall(SYS_fcntl, new, F_SETFD, FD_CLOEXEC);
+#else
+	while ((r=__syscall(SYS_dup3, old, new, flags))==-EBUSY);
+#endif
 	return __syscall_ret(r);
 }
 

src/unistd/fchown.c

@@ -13,5 +13,10 @@ int fchown(int fd, uid_t uid, gid_t gid)
 
 	char buf[15+3*sizeof(int)];
 	__procfdname(buf, fd);
+#ifdef SYS_chown
 	return syscall(SYS_chown, buf, uid, gid);
+#else
+	return syscall(SYS_fchownat, AT_FDCWD, buf, uid, gid);
+#endif
+
 }

src/unistd/getpgrp.c

@@ -3,5 +3,5 @@
 
 pid_t getpgrp(void)
 {
-	return __syscall(SYS_getpgrp);
+	return __syscall(SYS_getpgid, 0);
 }

src/unistd/lchown.c

 #include <unistd.h>
+#include <fcntl.h>
 #include "syscall.h"
 
 int lchown(const char *path, uid_t uid, gid_t gid)
 {
+#ifdef SYS_lchown
 	return syscall(SYS_lchown, path, uid, gid);
+#else
+	return syscall(SYS_fchownat, AT_FDCWD, path, uid, gid, AT_SYMLINK_NOFOLLOW);
+#endif
 }

src/unistd/link.c

 #include <unistd.h>
+#include <fcntl.h>
 #include "syscall.h"
 
 int link(const char *existing, const char *new)
 {
+#ifdef SYS_link
 	return syscall(SYS_link, existing, new);
+#else
+	return syscall(SYS_linkat, AT_FDCWD, existing, AT_FDCWD, new, 0);
+#endif
 }

src/unistd/pause.c

 #include <unistd.h>
+#include <signal.h>
 #include "syscall.h"
 #include "libc.h"
 
 int pause(void)
 {
+#ifdef SYS_pause
 	return syscall_cp(SYS_pause);
+#else
+	return syscall_cp(SYS_ppoll, 0, 0, 0, 0);
+#endif
 }

src/unistd/pipe.c

@@ -3,5 +3,9 @@
 
 int pipe(int fd[2])
 {
+#ifdef SYS_pipe
 	return syscall(SYS_pipe, fd);
+#else
+	return syscall(SYS_pipe2, fd, 0);
+#endif
 }

src/unistd/readlink.c

 #include <unistd.h>
+#include <fcntl.h>
 #include "syscall.h"
 
 ssize_t readlink(const char *restrict path, char *restrict buf, size_t bufsize)
 {
+#ifdef SYS_readlink
 	return syscall(SYS_readlink, path, buf, bufsize);
+#else
+	return syscall(SYS_readlinkat, AT_FDCWD, path, buf, bufsize);
+#endif
 }

src/unistd/rmdir.c

 #include <unistd.h>
+#include <fcntl.h>
 #include "syscall.h"
 
 int rmdir(const char *path)
 {
+#ifdef SYS_rmdir
 	return syscall(SYS_rmdir, path);
+#else
+	return syscall(SYS_unlinkat, AT_FDCWD, path, AT_REMOVEDIR);
+#endif
 }

src/unistd/symlink.c

 #include <unistd.h>
+#include <fcntl.h>
 #include "syscall.h"
 
 int symlink(const char *existing, const char *new)
 {
+#ifdef SYS_symlink
 	return syscall(SYS_symlink, existing, new);
+#else
+	return syscall(SYS_symlinkat, existing, AT_FDCWD, new);
+#endif
 }

src/unistd/unlink.c

 #include <unistd.h>
+#include <fcntl.h>
 #include "syscall.h"
 
 int unlink(const char *path)
 {
+#ifdef SYS_unlink
 	return syscall(SYS_unlink, path);
+#else
+	return syscall(SYS_unlinkat, AT_FDCWD, path, 0);
+#endif
 }