[libc] Implement sched_getcpu (#195001)

This is extremely similar to getcpu, but was available in a much earlier
glibc, so a lot more code depends on it. Do a similar implementation. We
can only have a simple smoke test as the only documented failure mode in
the man page is running on a kernel that does not support the system
call, and such kernels (<2.6) are ancient at this point.

libc/config/linux/aarch64/entrypoints.txt

@@ -39,6 +39,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.sched.sched_get_priority_max
     libc.src.sched.sched_get_priority_min
     libc.src.sched.sched_getaffinity
+    libc.src.sched.sched_getcpu
     libc.src.sched.sched_getparam
     libc.src.sched.sched_getscheduler
     libc.src.sched.sched_rr_get_interval

libc/config/linux/riscv/entrypoints.txt

@@ -39,6 +39,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.sched.sched_get_priority_max
     libc.src.sched.sched_get_priority_min
     libc.src.sched.sched_getaffinity
+    libc.src.sched.sched_getcpu
     libc.src.sched.sched_getparam
     libc.src.sched.sched_getscheduler
     libc.src.sched.sched_rr_get_interval

libc/config/linux/x86_64/entrypoints.txt

@@ -41,6 +41,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.sched.sched_get_priority_max
     libc.src.sched.sched_get_priority_min
     libc.src.sched.sched_getaffinity
+    libc.src.sched.sched_getcpu
     libc.src.sched.sched_getparam
     libc.src.sched.sched_getscheduler
     libc.src.sched.sched_rr_get_interval

libc/include/sched.yaml

@@ -75,6 +75,12 @@ functions:
       - type: pid_t
       - type: size_t
       - type: cpu_set_t *
+  - name: sched_getcpu
+    standards:
+      - GNUExtensions
+    return_type: int
+    arguments:
+      - type: void
   - name: sched_getparam
     standards:
       - POSIX

libc/src/sched/CMakeLists.txt

@@ -16,6 +16,13 @@ add_entrypoint_object(
     .${LIBC_TARGET_OS}.sched_getaffinity
 )
 
+add_entrypoint_object(
+  sched_getcpu
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.sched_getcpu
+)
+
 add_entrypoint_object(
   sched_setaffinity
   ALIAS

libc/src/sched/linux/CMakeLists.txt

@@ -24,6 +24,17 @@ add_entrypoint_object(
     libc.src.errno.errno
 )
 
+add_entrypoint_object(
+  sched_getcpu
+  SRCS
+    sched_getcpu.cpp
+  HDRS
+    ../sched_getcpu.h
+  DEPENDS
+    libc.src.__support.OSUtil.osutil
+    libc.src.errno.errno
+)
+
 add_entrypoint_object(
   sched_setaffinity
   SRCS

libc/src/sched/linux/sched_getcpu.cpp

@@ -0,0 +1,31 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/sched/sched_getcpu.h"
+
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/common.h"
+#include "src/__support/libc_errno.h"
+#include "src/__support/macros/config.h"
+
+#include <sys/syscall.h> // For syscall numbers.
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, sched_getcpu, ()) {
+  unsigned int cpu = 0;
+  int ret =
+      LIBC_NAMESPACE::syscall_impl<int>(SYS_getcpu, &cpu, nullptr, nullptr);
+  if (ret < 0) {
+    libc_errno = -ret;
+    return -1;
+  }
+  return cpu;
+}
+
+} // namespace LIBC_NAMESPACE_DECL

libc/src/sched/sched_getcpu.h

@@ -0,0 +1,20 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_SCHED_SCHED_GETCPU_H
+#define LLVM_LIBC_SRC_SCHED_SCHED_GETCPU_H
+
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int sched_getcpu(void);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_SCHED_SCHED_GETCPU_H

libc/test/src/sched/CMakeLists.txt

@@ -56,6 +56,18 @@ add_libc_unittest(
     libc.test.UnitTest.ErrnoCheckingTest
 )
 
+add_libc_unittest(
+  sched_getcpu_test
+  SUITE
+    libc_sched_unittests
+  SRCS
+    sched_getcpu_test.cpp
+  DEPENDS
+    libc.src.errno.errno
+    libc.src.sched.sched_getcpu
+    libc.test.UnitTest.ErrnoCheckingTest
+)
+
 add_libc_unittest(
   scheduler_test
   SUITE

libc/test/src/sched/sched_getcpu_test.cpp

@@ -0,0 +1,18 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/sched/sched_getcpu.h"
+#include "test/UnitTest/ErrnoCheckingTest.h"
+#include "test/UnitTest/ErrnoSetterMatcher.h"
+
+using LlvmLibcSchedSchedGetCpuTest = LIBC_NAMESPACE::testing::ErrnoCheckingTest;
+
+TEST_F(LlvmLibcSchedSchedGetCpuTest, SmokeTest) {
+  ASSERT_GE(LIBC_NAMESPACE::sched_getcpu(), 0);
+  ASSERT_ERRNO_SUCCESS();
+}