[libc] Add stub for confstr

libc/config/linux/aarch64/entrypoints.txt

@@ -392,6 +392,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.unistd.access
     libc.src.unistd.chdir
     libc.src.unistd.chown
+    libc.src.unistd.confstr
     libc.src.unistd.close
     libc.src.unistd.dup
     libc.src.unistd.dup2

libc/config/linux/arm/entrypoints.txt

@@ -228,6 +228,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.unistd.access
     libc.src.unistd.chdir
     libc.src.unistd.chown
+    libc.src.unistd.confstr
     libc.src.unistd.close
     libc.src.unistd.dup
     libc.src.unistd.dup2

libc/config/linux/riscv/entrypoints.txt

@@ -422,6 +422,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.unistd.access
     libc.src.unistd.chdir
     libc.src.unistd.chown
+    libc.src.unistd.confstr
     libc.src.unistd.close
     libc.src.unistd.dup
     libc.src.unistd.dup2

libc/config/linux/x86_64/entrypoints.txt

@@ -431,6 +431,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.unistd.access
     libc.src.unistd.chdir
     libc.src.unistd.chown
+    libc.src.unistd.confstr
     libc.src.unistd.close
     libc.src.unistd.dup
     libc.src.unistd.dup2

libc/include/unistd.yaml

@@ -103,6 +103,14 @@ functions:
       - type: const char *
       - type: uid_t
       - type: gid_t
+  - name: confstr
+    standards:
+      - posix
+    return_type: size_t
+    arguments:
+      - type: int
+      - type: char *
+      - type: size_t
   - name: close
     standards:
       - posix

libc/src/unistd/CMakeLists.txt

@@ -47,6 +47,22 @@ add_entrypoint_object(
     .${LIBC_TARGET_OS}.chown
 )
 
+add_entrypoint_object(
+  confstr
+  SRCS
+    confstr.cpp
+  HDRS
+    confstr.h
+  DEPENDS
+    libc.hdr.errno_macros
+    libc.hdr.types.size_t
+    libc.hdr.unistd_macros
+    libc.src.__support.common
+    libc.src.__support.libc_errno
+    libc.src.__support.macros.config
+    libc.src.errno.errno
+)
+
 add_entrypoint_object(
   close
   ALIAS

libc/src/unistd/confstr.cpp

@@ -0,0 +1,30 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+/// Implementation of confstr
+///
+//===----------------------------------------------------------------------===//
+
+#include "src/unistd/confstr.h"
+
+#include "hdr/errno_macros.h"
+#include "hdr/types/size_t.h"
+#include "hdr/unistd_macros.h"
+#include "src/__support/common.h"
+#include "src/__support/libc_errno.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(size_t, confstr, (int, char *, size_t)) {
+  libc_errno = EINVAL;
+  return 0;
+}
+
+} // namespace LIBC_NAMESPACE_DECL

libc/src/unistd/confstr.h

@@ -0,0 +1,26 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+/// Implementation header for confstr
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_UNISTD_CONFSTR_H
+#define LLVM_LIBC_SRC_UNISTD_CONFSTR_H
+
+#include "hdr/types/size_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+size_t confstr(int name, char *buf, size_t len);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_UNISTD_CONFSTR_H

libc/test/src/unistd/CMakeLists.txt

@@ -641,6 +641,20 @@ add_libc_test(
 )
 
 
+add_libc_test(
+  confstr_test
+  SUITE
+    libc_unistd_unittests
+  SRCS
+    confstr_test.cpp
+  DEPENDS
+    libc.hdr.errno_macros
+    libc.hdr.types.size_t
+    libc.src.unistd.confstr
+    libc.test.UnitTest.ErrnoCheckingTest
+    libc.test.UnitTest.ErrnoSetterMatcher
+)
+
 add_libc_test(
   sysconf_test
   SUITE

libc/test/src/unistd/confstr_test.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
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// Unittests for confstr
+///
+//===----------------------------------------------------------------------===//
+
+#include "src/unistd/confstr.h"
+
+#include "hdr/errno_macros.h"
+#include "hdr/types/size_t.h"
+#include "test/UnitTest/ErrnoCheckingTest.h"
+#include "test/UnitTest/ErrnoSetterMatcher.h"
+
+using LlvmLibcConfStrTest = LIBC_NAMESPACE::testing::ErrnoCheckingTest;
+using LIBC_NAMESPACE::testing::ErrnoSetterMatcher::Fails;
+
+TEST_F(LlvmLibcConfStrTest, InvalidName) {
+  char buf[64] = "initial";
+  EXPECT_THAT(LIBC_NAMESPACE::confstr(0, buf, sizeof(buf)),
+              Fails(EINVAL, size_t(0)));
+  EXPECT_THAT(LIBC_NAMESPACE::confstr(0, nullptr, 0), Fails(EINVAL, size_t(0)));
+  EXPECT_THAT(LIBC_NAMESPACE::confstr(-1, buf, sizeof(buf)),
+              Fails(EINVAL, size_t(0)));
+}