[libc] add printf

This patch adds the entrypoint for printf. With this, building a
"hello world" program with just LLVM-libc is possible.

Reviewed By: sivachandra

Differential Revision: https://reviews.llvm.org/D126831

libc/config/linux/x86_64/entrypoints.txt

@@ -280,6 +280,7 @@ if(LLVM_LIBC_FULL_BUILD)
     libc.src.stdio.sprintf
     libc.src.stdio.snprintf
     libc.src.stdio.fprintf
+    libc.src.stdio.printf
     libc.src.stdio.stderr
     libc.src.stdio.stdout
 

libc/src/stdio/CMakeLists.txt

@@ -261,3 +261,17 @@ add_entrypoint_object(
     libc.src.__support.arg_list
     libc.src.stdio.printf_core.vfprintf_internal
 )
+
+
+add_entrypoint_object(
+  printf
+  SRCS
+    printf.cpp
+  HDRS
+    printf.h
+  DEPENDS
+    libc.src.__support.File.file
+    libc.src.__support.File.platform_file
+    libc.src.__support.arg_list
+    libc.src.stdio.printf_core.vfprintf_internal
+)

libc/src/stdio/printf.cpp

@@ -0,0 +1,31 @@
+//===-- Implementation of printf --------------------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/stdio/printf.h"
+
+#include "src/__support/File/file.h"
+#include "src/__support/arg_list.h"
+#include "src/stdio/printf_core/vfprintf_internal.h"
+
+#include <stdarg.h>
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(int, printf, (const char *__restrict format, ...)) {
+  va_list vlist;
+  va_start(vlist, format);
+  internal::ArgList args(vlist); // This holder class allows for easier copying
+                                 // and pointer semantics, as well as handling
+                                 // destruction automatically.
+  va_end(vlist);
+  int ret_val = printf_core::vfprintf_internal(
+      reinterpret_cast<::FILE *>(__llvm_libc::stdout), format, args);
+  return ret_val;
+}
+
+} // namespace __llvm_libc

libc/src/stdio/printf.h

@@ -0,0 +1,20 @@
+//===-- Implementation header of printf -------------------------*- 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_STDIO_PRINTF_H
+#define LLVM_LIBC_SRC_STDIO_PRINTF_H
+
+#include <stdio.h>
+
+namespace __llvm_libc {
+
+int printf(const char *__restrict format, ...);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_STDIO_PRINTF_H

libc/test/src/stdio/CMakeLists.txt

@@ -97,6 +97,17 @@ add_libc_unittest(
     libc.src.stdio.fread
 )
 
+
+add_libc_unittest(
+  printf_test
+  SUITE
+    libc_stdio_unittests
+  SRCS
+    printf_test.cpp
+  DEPENDS
+    libc.src.stdio.printf
+)
+
 add_subdirectory(printf_core)
 
 add_subdirectory(testdata)

libc/test/src/stdio/printf_test.cpp

@@ -0,0 +1,29 @@
+//===-- Unittests for printf ---------------------------------------------===//
+//
+// 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/stdio/printf.h"
+
+#include "utils/UnitTest/Test.h"
+
+TEST(LlvmLibcPrintfTest, PrintOut) {
+  int written;
+
+  constexpr char simple[] = "A simple string with no conversions.\n";
+  written = __llvm_libc::printf(simple);
+  EXPECT_EQ(written, static_cast<int>(sizeof(simple) - 1));
+
+  constexpr char numbers[] = "1234567890\n";
+  written = __llvm_libc::printf("%s", numbers);
+  EXPECT_EQ(written, static_cast<int>(sizeof(numbers) - 1));
+
+  constexpr char format_more[] = "%s and more\n";
+  constexpr char short_numbers[] = "1234";
+  written = __llvm_libc::printf(format_more, short_numbers);
+  EXPECT_EQ(written,
+            static_cast<int>(sizeof(format_more) + sizeof(short_numbers) - 4));
+}