[libc] Add support for getpagesize. (llvm#171713)

As in the description.

Author: Sterling-Augustine

libc/config/linux/aarch64/entrypoints.txt

@@ -335,6 +335,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.unistd.getentropy
     libc.src.unistd.geteuid
     libc.src.unistd.gethostname
+    libc.src.unistd.getpagesize
     libc.src.unistd.getpid
     libc.src.unistd.getppid
     libc.src.unistd.getsid

libc/config/linux/riscv/entrypoints.txt

@@ -338,6 +338,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.unistd.getentropy
     libc.src.unistd.geteuid
     libc.src.unistd.gethostname
+    libc.src.unistd.getpagesize
     libc.src.unistd.getpid
     libc.src.unistd.getppid
     libc.src.unistd.getsid

libc/config/linux/x86_64/entrypoints.txt

@@ -347,6 +347,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.unistd.getentropy
     libc.src.unistd.geteuid
     libc.src.unistd.gethostname
+    libc.src.unistd.getpagesize
     libc.src.unistd.getpid
     libc.src.unistd.getppid
     libc.src.unistd.getsid

libc/include/unistd.yaml

@@ -174,6 +174,12 @@ functions:
     arguments:
       - type: char *
       - type: size_t
+  - name: getpagesize
+    standards:
+      - BSDExtensions
+    return_type: int
+    arguments:
+      - type: void
   - name: getopt
     standards:
       - POSIX

libc/src/unistd/CMakeLists.txt

@@ -139,6 +139,13 @@ add_entrypoint_object(
     .${LIBC_TARGET_OS}.gethostname
 )
 
+add_entrypoint_object(
+  getpagesize
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.getpagesize
+)
+
 add_entrypoint_object(
   getpid
   ALIAS

libc/src/unistd/getpagesize.h

@@ -0,0 +1,20 @@
+//===-- Implementation header for getpagesize -------------------*- 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_UNISTD_GETPAGESIZE_H
+#define LLVM_LIBC_SRC_UNISTD_GETPAGESIZE_H
+
+#include "src/__support/common.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int getpagesize();
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_UNISTD_GETPAGESIZE_H

libc/src/unistd/linux/CMakeLists.txt

@@ -249,6 +249,16 @@ add_entrypoint_object(
     libc.src.errno.errno
 )
 
+add_entrypoint_object(
+  getpagesize
+  SRCS
+    getpagesize.cpp
+  HDRS
+    ../getpagesize.h
+  DEPENDS
+    libc.src.__support.OSUtil.linux.auxv
+)
+
 add_entrypoint_object(
   geteuid
   SRCS

libc/src/unistd/linux/getpagesize.cpp

@@ -0,0 +1,25 @@
+//===-- Linux implementation of getpagesize -------------------------------===//
+//
+// 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/unistd/getpagesize.h"
+
+#include "src/__support/OSUtil/linux/auxv.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, getpagesize, ()) {
+  cpp::optional<unsigned long> page_size =
+      (LIBC_NAMESPACE::auxv::get(AT_PAGESZ));
+  if (page_size)
+    return static_cast<int>(*page_size);
+  return -1;
+}
+
+} // namespace LIBC_NAMESPACE_DECL

libc/test/src/unistd/CMakeLists.txt

@@ -477,6 +477,17 @@ add_libc_unittest(
     libc.test.UnitTest.ErrnoCheckingTest
 )
 
+add_libc_unittest(
+  getpagesize_test
+  SUITE
+    libc_unistd_unittests
+  SRCS
+    getpagesize_test.cpp
+  DEPENDS
+    libc.src.unistd.getpagesize
+    libc.test.UnitTest.ErrnoCheckingTest
+)
+
 add_libc_unittest(
   getgid_test
   SUITE

libc/test/src/unistd/getpagesize_test.cpp

@@ -0,0 +1,24 @@
+//===-- Unittests for getpagesize -----------------------------------------===//
+//
+// 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/unistd/getpagesize.h"
+
+#include "test/UnitTest/ErrnoCheckingTest.h"
+#include "test/UnitTest/Test.h"
+
+using LlvmLibcGetPageSizeTest = LIBC_NAMESPACE::testing::ErrnoCheckingTest;
+
+TEST(LlvmLibcGetPageSizeTest, GetPageSize) {
+  // getpagesize doesn't modify errno
+  int ret = LIBC_NAMESPACE::getpagesize();
+  ASSERT_NE(ret, -1);
+  ASSERT_NE(ret, 0);
+  // Correct page size depends on the hardware mode, but will be a modulus of
+  // 4096
+  ASSERT_EQ(ret % 4096, 0);
+}