[libc-commits] [libc] [libc] Add implementation of getcpu syscall wrapper (PR #150871)

Aiden Grossman via libc-commits libc-commits at lists.llvm.org
Tue Jul 29 06:35:52 PDT 2025 

https://github.com/boomanaiden154 updated https://github.com/llvm/llvm-project/pull/150871

>From 98d40ff15766b5fe719f8b7bceaa663e1302effa Mon Sep 17 00:00:00 2001
From: Aiden Grossman <aidengrossman at google.com>
Date: Mon, 28 Jul 2025 04:22:44 +0000
Subject: [PATCH 1/2] [libc] Add implementation of getcpu syscall wrapper

This patch adds the getcpu syscall wrapper. This has been supported in
glibc since v2.29.
---
 libc/config/linux/x86_64/entrypoints.txt |  1 +
 libc/include/sched.yaml                  |  7 ++++++
 libc/src/sched/CMakeLists.txt            |  7 ++++++
 libc/src/sched/getcpu.h                  | 21 +++++++++++++++++
 libc/src/sched/linux/CMakeLists.txt      | 12 ++++++++++
 libc/src/sched/linux/getcpu.cpp          | 30 ++++++++++++++++++++++++
 libc/test/src/sched/CMakeLists.txt       | 12 ++++++++++
 libc/test/src/sched/getcpu_test.cpp      | 29 +++++++++++++++++++++++
 8 files changed, 119 insertions(+)
 create mode 100644 libc/src/sched/getcpu.h
 create mode 100644 libc/src/sched/linux/getcpu.cpp
 create mode 100644 libc/test/src/sched/getcpu_test.cpp

diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index 5e8278e586286..a1e93a133f262 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -36,6 +36,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.poll.poll
 
     # sched.h entrypoints
+    libc.src.sched.getcpu
     libc.src.sched.sched_get_priority_max
     libc.src.sched.sched_get_priority_min
     libc.src.sched.sched_getaffinity
diff --git a/libc/include/sched.yaml b/libc/include/sched.yaml
index 57871f524bf11..f14799ddf33fa 100644
--- a/libc/include/sched.yaml
+++ b/libc/include/sched.yaml
@@ -18,6 +18,13 @@ functions:
     arguments:
       - type: size_t
       - type: const cpu_set_t *
+  - name: getcpu
+    standards:
+      - POSIX
+    return_type: int
+    arguments:
+      - type: unsigned int *
+      - type: unsigned int *
   - name: sched_get_priority_max
     standards:
       - POSIX
diff --git a/libc/src/sched/CMakeLists.txt b/libc/src/sched/CMakeLists.txt
index e6c37d3b0433a..d1d1de0718c56 100644
--- a/libc/src/sched/CMakeLists.txt
+++ b/libc/src/sched/CMakeLists.txt
@@ -2,6 +2,13 @@ if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
   add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
 endif()
 
+add_entrypoint_object(
+  getcpu
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.getcpu
+)
+
 add_entrypoint_object(
   sched_getaffinity
   ALIAS
diff --git a/libc/src/sched/getcpu.h b/libc/src/sched/getcpu.h
new file mode 100644
index 0000000000000..ed3187a68fadc
--- /dev/null
+++ b/libc/src/sched/getcpu.h
@@ -0,0 +1,21 @@
+//===-- Implementation header for getcpu ------------------------*- C++ -*-===//
+//
+// 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_GETCPU_H
+#define LLVM_LIBC_SRC_SCHED_GETCPU_H
+
+#include "src/__support/macros/config.h"
+#include <sched.h>
+
+namespace LIBC_NAMESPACE_DECL {
+
+int getcpu(unsigned int *cpu, unsigned int *node);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_SCHED_GETCPU_H
diff --git a/libc/src/sched/linux/CMakeLists.txt b/libc/src/sched/linux/CMakeLists.txt
index e690e76fd7483..66ebaeab43c21 100644
--- a/libc/src/sched/linux/CMakeLists.txt
+++ b/libc/src/sched/linux/CMakeLists.txt
@@ -1,3 +1,15 @@
+add_entrypoint_object(
+  getcpu
+  SRCS
+    getcpu.cpp
+  HDRS
+    ../getcpu.h
+  DEPENDS
+    libc.include.sched
+    libc.src.__support.OSUtil.osutil
+    libc.src.errno.errno
+)
+
 add_entrypoint_object(
   sched_getaffinity
   SRCS
diff --git a/libc/src/sched/linux/getcpu.cpp b/libc/src/sched/linux/getcpu.cpp
new file mode 100644
index 0000000000000..2726d2daca2c5
--- /dev/null
+++ b/libc/src/sched/linux/getcpu.cpp
@@ -0,0 +1,30 @@
+//===-- Implementation of getcpu ------------------------------------------===//
+//
+// 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/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 <sched.h>
+#include <sys/syscall.h> // For syscall numbers.
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, getcpu, (unsigned int *cpu, unsigned int *node)) {
+  int ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_getcpu, cpu, node);
+  if (ret < 0) {
+    libc_errno = -ret;
+    return -1;
+  }
+  return 0;
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/test/src/sched/CMakeLists.txt b/libc/test/src/sched/CMakeLists.txt
index 9dda4ea16e101..a5b00049df2ca 100644
--- a/libc/test/src/sched/CMakeLists.txt
+++ b/libc/test/src/sched/CMakeLists.txt
@@ -40,6 +40,18 @@ add_libc_unittest(
     libc.src.sched.sched_get_priority_max
 )
 
+add_libc_unittest(
+  getcpu_test
+  SUITE
+    libc_sched_unittests
+  SRCS
+    getcpu_test.cpp
+  DEPENDS
+    libc.include.sched
+    libc.src.errno.errno
+    libc.src.sched.getcpu
+)
+
 add_libc_unittest(
   scheduler_test
   SUITE
diff --git a/libc/test/src/sched/getcpu_test.cpp b/libc/test/src/sched/getcpu_test.cpp
new file mode 100644
index 0000000000000..5c3f531f76f72
--- /dev/null
+++ b/libc/test/src/sched/getcpu_test.cpp
@@ -0,0 +1,29 @@
+//===-- Unittests for getcpu ----------------------------------------------===//
+//
+// 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/__support/OSUtil/syscall.h"
+#include "src/__support/libc_errno.h"
+#include "src/sched/getcpu.h"
+#include "test/UnitTest/ErrnoSetterMatcher.h"
+
+#include <sched.h>
+
+TEST(LlvmLibcSchedGetCpuTest, SmokeTest) {
+  unsigned int current_cpu;
+  unsigned int current_node;
+  using LIBC_NAMESPACE::testing::ErrnoSetterMatcher::Succeeds;
+  ASSERT_THAT(LIBC_NAMESPACE::getcpu(&current_cpu, &current_node), Succeeds(0));
+}
+
+TEST(LlvmLibcSchedGetCpuTest, BadPointer) {
+  unsigned int current_cpu;
+  unsigned int *current_node = reinterpret_cast<unsigned int *>(-1);
+  using LIBC_NAMESPACE::testing::ErrnoSetterMatcher::Fails;
+  ASSERT_THAT(LIBC_NAMESPACE::getcpu(&current_cpu, current_node),
+              Fails(EFAULT));
+}

>From fb71929b7109fd52ec997a5e0df3956dc775ad2c Mon Sep 17 00:00:00 2001
From: Aiden Grossman <aidengrossman at google.com>
Date: Tue, 29 Jul 2025 13:35:40 +0000
Subject: [PATCH 2/2] feedback

---
 libc/src/sched/getcpu.h             | 1 -
 libc/src/sched/linux/getcpu.cpp     | 1 -
 libc/test/src/sched/CMakeLists.txt  | 1 +
 libc/test/src/sched/getcpu_test.cpp | 4 +++-
 4 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/libc/src/sched/getcpu.h b/libc/src/sched/getcpu.h
index ed3187a68fadc..4c90e646c7e7b 100644
--- a/libc/src/sched/getcpu.h
+++ b/libc/src/sched/getcpu.h
@@ -10,7 +10,6 @@
 #define LLVM_LIBC_SRC_SCHED_GETCPU_H
 
 #include "src/__support/macros/config.h"
-#include <sched.h>
 
 namespace LIBC_NAMESPACE_DECL {
 
diff --git a/libc/src/sched/linux/getcpu.cpp b/libc/src/sched/linux/getcpu.cpp
index 2726d2daca2c5..302e9fb6cacc6 100644
--- a/libc/src/sched/linux/getcpu.cpp
+++ b/libc/src/sched/linux/getcpu.cpp
@@ -13,7 +13,6 @@
 #include "src/__support/libc_errno.h"
 #include "src/__support/macros/config.h"
 
-#include <sched.h>
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace LIBC_NAMESPACE_DECL {
diff --git a/libc/test/src/sched/CMakeLists.txt b/libc/test/src/sched/CMakeLists.txt
index a5b00049df2ca..54c6d1d4f52c6 100644
--- a/libc/test/src/sched/CMakeLists.txt
+++ b/libc/test/src/sched/CMakeLists.txt
@@ -50,6 +50,7 @@ add_libc_unittest(
     libc.include.sched
     libc.src.errno.errno
     libc.src.sched.getcpu
+    libc.test.UnitTest.ErrnoCheckingTest
 )
 
 add_libc_unittest(
diff --git a/libc/test/src/sched/getcpu_test.cpp b/libc/test/src/sched/getcpu_test.cpp
index 5c3f531f76f72..0e6806673a214 100644
--- a/libc/test/src/sched/getcpu_test.cpp
+++ b/libc/test/src/sched/getcpu_test.cpp
@@ -9,15 +9,17 @@
 #include "src/__support/OSUtil/syscall.h"
 #include "src/__support/libc_errno.h"
 #include "src/sched/getcpu.h"
+#include "test/UnitTest/ErrnoCheckingTest.h"
 #include "test/UnitTest/ErrnoSetterMatcher.h"
 
-#include <sched.h>
+using LlvmLibcSchedGetCpuTest = LIBC_NAMESPACE::testing::ErrnoCheckingTest;
 
 TEST(LlvmLibcSchedGetCpuTest, SmokeTest) {
   unsigned int current_cpu;
   unsigned int current_node;
   using LIBC_NAMESPACE::testing::ErrnoSetterMatcher::Succeeds;
   ASSERT_THAT(LIBC_NAMESPACE::getcpu(&current_cpu, &current_node), Succeeds(0));
+  ASSERT_ERRNO_SUCCESS();
 }
 
 TEST(LlvmLibcSchedGetCpuTest, BadPointer) {

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