Commit e3c3bf2b58 introduce use of pselect6, but has following disadvantages:
* Use of userspace types in args67 structure - it breaks, for example,
configs when 32-bit uClibc-ng compiled against 64-bit kernel. Syscall
will always return EINVAL. We must use __kernel_* types and
__SYSCALL_SIGSET_T_SIZE.
* It have excess checks for NSEC_PER_SEC. Original code from select()
implementation has struct timeval => struct timespec conversion,
kernel select() syscall implementation do the same.
But none of libc versions (glibc, eglibc, musl) I know, perform similar
checks for pselect() - there is no structure fields conversions,
just struct timespec through all the calls.
To have such checks in uClibc-ng we need one example, at least.
* It is possible to avoid extra userspace reads from kernel code if
sigmask == NULL. I suggest to do it, for a few bytes cost.
* Commit didn't add test case to testsuite.
Signed-off-by: Leonid Lisovskiy <lly.dev@gmail.com>
---
libc/sysdeps/linux/common/pselect.c | 67 ++++++++++++-------------------------
test/unistd/tst-pselect.c | 51 ++++++++++++++++++++++++++++
2 files changed, 73 insertions(+), 45 deletions(-)
create mode 100644 test/unistd/tst-pselect.c
diff --git a/libc/sysdeps/linux/common/pselect.c b/libc/sysdeps/linux/common/pselect.c
index 3f1dd28..fbe85b7 100644
--- a/libc/sysdeps/linux/common/pselect.c
+++ b/libc/sysdeps/linux/common/pselect.c
@@ -31,55 +31,32 @@ static int __NC(pselect)(int nfds, fd_set *readfds, fd_set *writefds,
const sigset_t *sigmask)
{
#ifdef __NR_pselect6
-#define NSEC_PER_SEC 1000000000L
- struct timespec _ts, *ts = 0;
- if (timeout) {
- /* The Linux kernel can in some situations update the timeout value.
- * We do not want that so use a local variable.
- */
+ /* The Linux kernel can in some situations update the timeout value.
+ * We do not want that so use a local variable.
+ */
+ struct timespec _ts;
+
+ if (timeout != NULL) {
_ts = *timeout;
+ timeout = &_ts;
+ }
+ /* Note: the system call expects 7 values but on most architectures
+ we can only pass in 6 directly. If there is an architecture with
+ support for more parameters a new version of this file needs to
+ be created. */
+ struct {
+ __kernel_ulong_t ss;
+ __kernel_size_t ss_len;
+ } data;
- /* GNU extension: allow for timespec values where the sub-sec
- * field is equal to or more than 1 second. The kernel will
- * reject this on us, so take care of the time shift ourself.
- * Some applications (like readline and linphone) do this.
- * See 'clarification on select() type calls and invalid timeouts'
- * on the POSIX general list for more information.
- */
- if (_ts.tv_nsec >= NSEC_PER_SEC) {
- _ts.tv_sec += _ts.tv_nsec / NSEC_PER_SEC;
- _ts.tv_nsec %= NSEC_PER_SEC;
- }
-
- ts = &_ts;
+ if (sigmask != NULL) {
+ data.ss = (__kernel_ulong_t) sigmask;
+ data.ss_len = __SYSCALL_SIGSET_T_SIZE;
+
+ sigmask = (void *)&data;
}
- /* The pselect6 syscall API is strange. It wants a 7th arg to be
- * the sizeof(*sigmask). However syscalls with > 6 arguments aren't
- * supported on linux. So arguments 6 and 7 are stuffed in a struct
- * and a pointer to that struct is passed as the 6th argument to
- * the syscall.
- * Glibc stuffs arguments 6 and 7 in a ulong[2]. Linux reads
- * them as if there were a struct { sigset_t*; size_t } in
- * userspace. There woudl be trouble if userspace and the kernel are
- * compiled differently enough that size_t isn't the same as ulong,
- * but not enough to trigger the compat layer in linux. I can't
- * think of such a case, so I'm using linux's struct.
- * Furthermore Glibc sets the sigsetsize to _NSIG/8. However linux
- * checks for sizeof(sigset_t), which internally is a ulong array.
- * This means that if _NSIG isn't a multiple of BITS_PER_LONG then
- * linux will refuse glibc's value. So I prefer sizeof(sigset_t) for
- * the value of sigsetsize.
- */
- struct {
- const sigset_t *sigmask;
- size_t sigsetsize;
- } args67 = {
- sigmask,
- sizeof(sigset_t),
- };
-
- return INLINE_SYSCALL(pselect6, 6, nfds, readfds, writefds, exceptfds, ts, &args67);
+ return INLINE_SYSCALL(pselect6, 6, nfds, readfds, writefds, exceptfds, timeout, sigmask);
#else
struct timeval tval;
int retval;
diff --git a/test/unistd/tst-pselect.c b/test/unistd/tst-pselect.c
new file mode 100644
index 0000000..cab9451
--- /dev/null
+++ b/test/unistd/tst-pselect.c
@@ -0,0 +1,51 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <errno.h>
+#include <signal.h>
+#include <sys/types.h>
+#include <sys/select.h>
+
+// our SIGALRM handler
+void handler(int signum) {
+ (void)signum;
+ puts("got signal\n");
+}
+
+static int
+do_test (void)
+{
+ int rc;
+ sigset_t wait_mask, mask_sigchld;
+ struct sigaction act;
+
+ // block SIGALRM. We want to handle it only when we're ready
+ sigemptyset(&mask_sigchld);
+ sigaddset(&mask_sigchld, SIGALRM);
+ sigprocmask(SIG_BLOCK, &mask_sigchld, &wait_mask);
+ sigdelset(&wait_mask, SIGALRM);
+
+ // register a signal handler so we can see when the signal arrives
+ memset(&act, 0, sizeof(act));
+ sigemptyset(&act.sa_mask); // just in case an empty set isn't all 0's (total paranoia)
+ act.sa_handler = handler;
+ sigaction(SIGALRM, &act, NULL);
+
+ // send ourselves a SIGARLM. It will pend until we unblock that signal in pselect()
+ printf("sending ourselves a signal\n");
+ kill(getpid(), SIGALRM);
+
+ printf("signal is pending; calling pselect()\n");
+ rc = pselect(0, NULL, NULL, NULL, NULL, &wait_mask);
+ if (rc != -1 || errno != EINTR) {
+ int e = errno;
+ printf("pselect() returned %d, errno %d (%s)\n", rc, e, strerror(e));
+ exit(1);
+ }
+
+ return 0;
+}
+
+#define TEST_FUNCTION do_test ()
+#include <test-skeleton.c>
--
1.8.5.6