[libc] implement unistd/getentropy

libc/config/linux/aarch64/entrypoints.txt

@@ -322,6 +322,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.unistd.fsync
     libc.src.unistd.ftruncate
     libc.src.unistd.getcwd
+    libc.src.unistd.getentropy
     libc.src.unistd.geteuid
     libc.src.unistd.getpid
     libc.src.unistd.getppid

libc/config/linux/x86_64/entrypoints.txt

@@ -321,6 +321,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.unistd.fsync
     libc.src.unistd.ftruncate
     libc.src.unistd.getcwd
+    libc.src.unistd.getentropy
     libc.src.unistd.geteuid
     libc.src.unistd.getpid
     libc.src.unistd.getppid

libc/include/unistd.yaml

@@ -128,6 +128,13 @@ functions:
     arguments:
       - type: char *
       - type: size_t
+  - name: getentropy
+    standards:
+      - GNUExtensions
+    return_type: int
+    arguments:
+      - type: void *
+      - type: size_t
   - name: geteuid
     standards:
       - POSIX

libc/src/unistd/CMakeLists.txt

@@ -350,3 +350,10 @@ add_entrypoint_object(
   DEPENDS
     libc.src.__support.threads.identifier
 )
+
+add_entrypoint_object(
+  getentropy
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.getentropy
+)

libc/src/unistd/getentropy.h

@@ -0,0 +1,19 @@
+//===-- Implementation header for getentropy ------------------------------===//
+//
+// 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 "hdr/types/size_t.h"
+#include "src/__support/common.h"
+
+#ifndef LLVM_LIBC_SRC_UNISTD_GETENTROPY_H
+#define LLVM_LIBC_SRC_UNISTD_GETENTROPY_H
+
+namespace LIBC_NAMESPACE_DECL {
+int getentropy(void *buffer, size_t length);
+}
+
+#endif // LLVM_LIBC_SRC_UNISTD_GETENTROPY_H

libc/src/unistd/linux/CMakeLists.txt

@@ -570,3 +570,17 @@ add_entrypoint_object(
     libc.src.__support.OSUtil.osutil
     libc.src.errno.errno
 )
+
+add_entrypoint_object(
+  getentropy
+  SRCS
+    getentropy.cpp
+  HDRS
+    ../getentropy.h
+  DEPENDS
+    libc.hdr.types.size_t
+    libc.hdr.types.ssize_t
+    libc.hdr.errno_macros
+    libc.src.sys.random.getrandom
+    libc.src.errno.errno
+)

libc/src/unistd/linux/getentropy.cpp

@@ -0,0 +1,48 @@
+//===-- Linux implementation of getentropy --------------------------------===//
+//
+// 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/getentropy.h"
+#include "hdr/errno_macros.h"
+#include "src/__support/common.h"
+#include "src/errno/libc_errno.h"
+#include "src/sys/random/getrandom.h"
+
+namespace LIBC_NAMESPACE_DECL {
+LLVM_LIBC_FUNCTION(int, getentropy, (void *buffer, size_t length)) {
+  // check the length limit
+  if (length > 256) {
+    libc_errno = EIO;
+    return -1;
+  }
+
+  char *cursor = static_cast<char *>(buffer);
+  while (length != 0) {
+    // 0 flag means urandom and blocking, which meets the assumption of
+    // getentropy
+    ssize_t ret = LIBC_NAMESPACE::getrandom(cursor, length, 0);
+
+    // on success, advance the buffer pointer
+    if (ret != -1) {
+      length -= static_cast<size_t>(ret);
+      cursor += ret;
+      continue;
+    }
+
+    // on EINTR, try again
+    if (libc_errno == EINTR)
+      continue;
+
+    // on ENOSYS, forward errno and exit;
+    // otherwise, set EIO and exit
+    if (libc_errno != ENOSYS)
+      libc_errno = EIO;
+    return -1;
+  }
+  return 0;
+}
+} // namespace LIBC_NAMESPACE_DECL

libc/test/src/unistd/CMakeLists.txt

@@ -488,6 +488,18 @@ add_libc_test(
     libc.src.stdio.fflush
 )
 
+add_libc_test(
+  getentropy_test
+  SUITE
+    libc_unistd_unittests
+  SRCS
+    getentropy_test.cpp
+  DEPENDS
+    libc.src.unistd.getentropy
+    libc.src.errno.errno
+    libc.test.UnitTest.ErrnoSetterMatcher
+)
+
 if(LLVM_LIBC_FULL_BUILD)
   add_libc_test(
     _exit_test

libc/test/src/unistd/getentropy_test.cpp

@@ -0,0 +1,33 @@
+//===-- Unittests for getentropy ------------------------------------------===//
+//
+// 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/errno/libc_errno.h"
+#include "src/unistd/getentropy.h"
+#include "test/UnitTest/ErrnoSetterMatcher.h"
+#include "test/UnitTest/Test.h"
+
+using namespace LIBC_NAMESPACE::testing::ErrnoSetterMatcher;
+
+TEST(LlvmLibcUnistdGetEntropyTest, LengthTooLong) {
+  char buf[1024];
+  ASSERT_THAT(LIBC_NAMESPACE::getentropy(buf, 257), Fails(EIO));
+  ASSERT_THAT(LIBC_NAMESPACE::getentropy(buf, 1024), Fails(EIO));
+}
+
+TEST(LlvmLibcUnistdGetEntropyTest, SmokeTest) {
+  char buf[256];
+  ASSERT_THAT(LIBC_NAMESPACE::getentropy(buf, 256), Succeeds());
+  ASSERT_THAT(LIBC_NAMESPACE::getentropy(buf, 0), Succeeds());
+  ASSERT_THAT(LIBC_NAMESPACE::getentropy(buf, 1), Succeeds());
+  ASSERT_THAT(LIBC_NAMESPACE::getentropy(buf, 16), Succeeds());
+  ASSERT_THAT(LIBC_NAMESPACE::getentropy(buf, 17), Succeeds());
+}
+
+TEST(LlvmLibcUnistdGetEntropyTest, OtherError) {
+  ASSERT_THAT(LIBC_NAMESPACE::getentropy(nullptr, 1), Fails(EIO));
+}