[libc] Provide vprintf for baremetal (llvm#95363)

This is similar to baremetal printf that was implemented in llvm#94078.

Author: petrhosek

libc/src/stdio/CMakeLists.txt

@@ -22,7 +22,7 @@ if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
   add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
 endif()
 
-if(NOT LIBC_TARGET_OS_IS_GPU)
+if(NOT LIBC_TARGET_OS_IS_BAREMETAL AND NOT LIBC_TARGET_OS_IS_GPU)
   add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/generic)
 endif()
 

libc/src/stdio/baremetal/CMakeLists.txt

@@ -31,3 +31,16 @@ add_entrypoint_object(
     libc.src.__support.OSUtil.osutil
     libc.src.__support.CPP.string_view
 )
+
+add_entrypoint_object(
+  vprintf
+  SRCS
+    vprintf.cpp
+  HDRS
+    ../vprintf.h
+  DEPENDS
+    libc.src.stdio.printf_core.printf_main
+    libc.src.stdio.printf_core.writer
+    libc.src.__support.arg_list
+    libc.src.__support.OSUtil.osutil
+)

libc/src/stdio/baremetal/vprintf.cpp

@@ -0,0 +1,49 @@
+//===-- Implementation of vprintf -------------------------------*- 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/vprintf.h"
+#include "src/__support/OSUtil/io.h"
+#include "src/__support/arg_list.h"
+#include "src/stdio/printf_core/core_structs.h"
+#include "src/stdio/printf_core/printf_main.h"
+#include "src/stdio/printf_core/writer.h"
+
+#include <stdarg.h>
+
+namespace LIBC_NAMESPACE {
+
+namespace {
+
+LIBC_INLINE int raw_write_hook(cpp::string_view new_str, void *) {
+  write_to_stderr(new_str);
+  return printf_core::WRITE_OK;
+}
+
+} // namespace
+
+LLVM_LIBC_FUNCTION(int, vprintf,
+                   (const char *__restrict format, va_list vlist)) {
+  internal::ArgList args(vlist); // This holder class allows for easier copying
+                                 // and pointer semantics, as well as handling
+                                 // destruction automatically.
+  constexpr size_t BUFF_SIZE = 1024;
+  char buffer[BUFF_SIZE];
+
+  printf_core::WriteBuffer wb(buffer, BUFF_SIZE, &raw_write_hook, nullptr);
+  printf_core::Writer writer(&wb);
+
+  int retval = printf_core::printf_main(&writer, format, args);
+
+  int flushval = wb.overflow_write("");
+  if (flushval != printf_core::WRITE_OK)
+    retval = flushval;
+
+  return retval;
+}
+
+} // namespace LIBC_NAMESPACE