[libc-commits] [libc] [libc] Implement ppoll in poll (PR #225767)

[Pavel Labath via libc-commits]

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@@ -0,0 +1,59 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// Syscall wrapper for ppoll.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC___SUPPORT_OSUTIL_SYSCALL_WRAPPERS_PPOLL_H
+#define LLVM_LIBC_SRC___SUPPORT_OSUTIL_SYSCALL_WRAPPERS_PPOLL_H
+
+#include "hdr/signal_macros.h"
+#include "hdr/types/nfds_t.h"
+#include "hdr/types/sigset_t.h"
+#include "hdr/types/struct_pollfd.h"
+#include "hdr/types/struct_timespec.h"
+#include "src/__support/OSUtil/linux/syscall.h" // syscall_checked
+#include "src/__support/common.h"
+#include "src/__support/error_or.h"
+#include "src/__support/macros/config.h"
+#include <sys/syscall.h>
+
+namespace LIBC_NAMESPACE_DECL {
+namespace linux_syscalls {
+
+LIBC_INLINE ErrorOr<int> ppoll(struct pollfd *fds, nfds_t nfds,
+                               const struct timespec *__restrict tmo_p,
+                               const sigset_t *__restrict sigmask) {
+#if defined(SYS_ppoll_time64)
+  static_assert(
+      sizeof(time_t) == sizeof(int64_t),
+      "SYS_ppoll_time64 requires struct timespec with 64-bit members.");
+  // The kernel expects the signal mask size in bytes, not the number of
+  // signals. NSIG is the signal count, so NSIG / 8 gives the byte size.
+  return syscall_checked<int>(SYS_ppoll_time64, fds, nfds, tmo_p, sigmask,
+                              NSIG / 8);
+#elif defined(SYS_ppoll)
+  static_assert(
+      sizeof(timespec::tv_nsec) == sizeof(long),
+      "This legacy syscall fallback is only safe on platforms where tv_nsec "
+      "matches the register size (long). It is unsafe on 32-bit platforms "
+      "with 64-bit tv_nsec.");
+  // The kernel expects the signal mask size in bytes, not the number of
+  // signals. NSIG is the signal count, so NSIG / 8 gives the byte size.
----------------
labath wrote:

Assign NSIG/8 to a local (const) variable before the #if block, so you don't have to repeat this comment.

Alternatively, I'd also be fine with using sizeof(sigmask) instead -- and then I don't think you need the comment.

https://github.com/llvm/llvm-project/pull/225767