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.

2 files changed, 26 insertions, 0 deletions

diff --git a/src/select/poll.c b/src/select/poll.c
index f1e73e82..9e0bcbd8 100644
--- a/src/select/poll.c
+++ b/src/select/poll.c
@@ -1,8 +1,16 @@
 #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
 }
diff --git a/src/select/select.c b/src/select/select.c
index f93597b5..7b5f6dcf 100644
--- a/src/select/select.c
+++ b/src/select/select.c
@@ -1,8 +1,26 @@
 #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
 }