summaryrefslogtreecommitdiff
path: root/libc
diff options
context:
space:
mode:
authorLeonid Lisovskiy <lly.dev@gmail.com>2015-12-27 17:46:49 (GMT)
committerWaldemar Brodkorb <wbx@uclibc-ng.org>2016-01-01 18:48:17 (GMT)
commitd1b1ccb72f4dee5728f0878054709721b1163f62 (patch)
tree862e6231c4472e83b911d6794f11ee6b4e84efe7 /libc
parenta65637cc30455841909b2676599589b702bd654e (diff)
Fix "pselect: Use linux pselect6 syscall when available"
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>
Diffstat (limited to 'libc')
-rw-r--r--libc/sysdeps/linux/common/pselect.c67
1 files changed, 22 insertions, 45 deletions
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;