[libc] Support for scanf on baremetal (llvm#131043)

This uses the templatized scanf Reader interface introduced in llvm#131037.

Author: petrhosek

libc/config/baremetal/aarch64/entrypoints.txt

@@ -123,18 +123,22 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.inttypes.strtoumax
 
     # stdio.h entrypoints
+    libc.src.stdio.asprintf
     libc.src.stdio.getchar
     libc.src.stdio.printf
     libc.src.stdio.putchar
     libc.src.stdio.puts
     libc.src.stdio.remove
+    libc.src.stdio.scanf
     libc.src.stdio.snprintf
     libc.src.stdio.sprintf
-    libc.src.stdio.asprintf
+    libc.src.stdio.sscanf
+    libc.src.stdio.vasprintf
     libc.src.stdio.vprintf
+    libc.src.stdio.vscanf
     libc.src.stdio.vsnprintf
     libc.src.stdio.vsprintf
-    libc.src.stdio.vasprintf
+    libc.src.stdio.vsscanf
 
     # stdbit.h entrypoints
     libc.src.stdbit.stdc_bit_ceil_uc

libc/config/baremetal/arm/entrypoints.txt

@@ -123,18 +123,22 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.inttypes.strtoumax
 
     # stdio.h entrypoints
+    libc.src.stdio.asprintf
     libc.src.stdio.getchar
     libc.src.stdio.printf
     libc.src.stdio.putchar
     libc.src.stdio.puts
     libc.src.stdio.remove
+    libc.src.stdio.scanf
     libc.src.stdio.snprintf
     libc.src.stdio.sprintf
-    libc.src.stdio.asprintf
+    libc.src.stdio.sscanf
+    libc.src.stdio.vasprintf
     libc.src.stdio.vprintf
+    libc.src.stdio.vscanf
     libc.src.stdio.vsnprintf
     libc.src.stdio.vsprintf
-    libc.src.stdio.vasprintf
+    libc.src.stdio.vsscanf
 
     # stdbit.h entrypoints
     libc.src.stdbit.stdc_bit_ceil_uc

libc/config/baremetal/riscv/entrypoints.txt

@@ -119,18 +119,22 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.inttypes.strtoumax
 
     # stdio.h entrypoints
+    libc.src.stdio.asprintf
     libc.src.stdio.getchar
     libc.src.stdio.printf
     libc.src.stdio.putchar
     libc.src.stdio.puts
     libc.src.stdio.remove
+    libc.src.stdio.scanf
     libc.src.stdio.snprintf
     libc.src.stdio.sprintf
-    libc.src.stdio.asprintf
+    libc.src.stdio.sscanf
+    libc.src.stdio.vasprintf
     libc.src.stdio.vprintf
+    libc.src.stdio.vscanf
     libc.src.stdio.vsnprintf
     libc.src.stdio.vsprintf
-    libc.src.stdio.vasprintf
+    libc.src.stdio.vsscanf
 
     # stdbit.h entrypoints
     libc.src.stdbit.stdc_bit_ceil_uc

libc/src/stdio/CMakeLists.txt

@@ -95,20 +95,6 @@ add_entrypoint_object(
     libc.src.__support.File.platform_file
 )
 
-list(APPEND scanf_deps
-      libc.src.__support.arg_list
-      libc.src.stdio.scanf_core.vfscanf_internal
-      libc.hdr.types.FILE
-)
-
-if(LLVM_LIBC_FULL_BUILD AND NOT LIBC_TARGET_OS_IS_GPU)
-  list(APPEND scanf_deps
-      libc.src.__support.File.file
-      libc.src.__support.File.platform_file
-      libc.src.__support.File.platform_stdin
-  )
-endif()
-
 add_entrypoint_object(
   sscanf
   SRCS
@@ -133,46 +119,6 @@ add_entrypoint_object(
     libc.src.stdio.scanf_core.string_reader
 )
 
-add_entrypoint_object(
-  fscanf
-  SRCS
-    fscanf.cpp
-  HDRS
-    fscanf.h
-  DEPENDS
-    ${scanf_deps}
-)
-
-add_entrypoint_object(
-  vfscanf
-  SRCS
-    vfscanf.cpp
-  HDRS
-    vfscanf.h
-  DEPENDS
-    ${scanf_deps}
-)
-
-add_entrypoint_object(
-  scanf
-  SRCS
-    scanf.cpp
-  HDRS
-    scanf.h
-  DEPENDS
-    ${scanf_deps}
-)
-
-add_entrypoint_object(
-  vscanf
-  SRCS
-    vscanf.cpp
-  HDRS
-    vscanf.h
-  DEPENDS
-    ${scanf_deps}
-)
-
 add_entrypoint_object(
   sprintf
   SRCS
@@ -295,8 +241,12 @@ add_stdio_entrypoint_object(getchar)
 add_stdio_entrypoint_object(getchar_unlocked)
 add_stdio_entrypoint_object(fgets)
 add_stdio_entrypoint_object(ungetc)
+add_stdio_entrypoint_object(scanf)
+add_stdio_entrypoint_object(fscanf)
 add_stdio_entrypoint_object(stdin)
 add_stdio_entrypoint_object(stdout)
 add_stdio_entrypoint_object(stderr)
 add_stdio_entrypoint_object(vprintf)
 add_stdio_entrypoint_object(vfprintf)
+add_stdio_entrypoint_object(vscanf)
+add_stdio_entrypoint_object(vfscanf)

libc/src/stdio/baremetal/CMakeLists.txt

@@ -55,6 +55,28 @@ add_entrypoint_object(
     libc.src.__support.CPP.string_view
 )
 
+add_header_library(
+  scanf_internal
+  HDRS
+    scanf_internal.h
+  DEPENDS
+    libc.src.stdio.scanf_core.reader
+    libc.src.__support.OSUtil.osutil
+)
+
+add_entrypoint_object(
+  scanf
+  SRCS
+    scanf.cpp
+  HDRS
+    ../scanf.h
+  DEPENDS
+    .scanf_internal
+    libc.src.stdio.scanf_core.scanf_main
+    libc.src.__support.arg_list
+    libc.src.__support.OSUtil.osutil
+)
+
 add_entrypoint_object(
   vprintf
   SRCS
@@ -67,3 +89,16 @@ add_entrypoint_object(
     libc.src.__support.arg_list
     libc.src.__support.OSUtil.osutil
 )
+
+add_entrypoint_object(
+  vscanf
+  SRCS
+    vscanf.cpp
+  HDRS
+    ../vscanf.h
+  DEPENDS
+    .scanf_internal
+    libc.src.stdio.scanf_core.scanf_main
+    libc.src.__support.arg_list
+    libc.src.__support.OSUtil.osutil
+)

libc/src/stdio/baremetal/getchar.cpp

@@ -17,7 +17,7 @@ namespace LIBC_NAMESPACE_DECL {
 LLVM_LIBC_FUNCTION(int, getchar, ()) {
   char buf[1];
   auto result = read_from_stdin(buf, sizeof(buf));
-  if (result < 0)
+  if (result <= 0)
     return EOF;
   return buf[0];
 }

libc/src/stdio/baremetal/scanf.cpp

@@ -0,0 +1,37 @@
+//===-- Implementation of scanf ---------------------------------*- 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/scanf.h"
+
+#include "hdr/stdio_macros.h"
+#include "src/__support/OSUtil/io.h"
+#include "src/__support/arg_list.h"
+#include "src/__support/macros/config.h"
+#include "src/stdio/baremetal/scanf_internal.h"
+#include "src/stdio/scanf_core/scanf_main.h"
+
+#include <stdarg.h>
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, scanf, (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);
+
+  scanf_core::StdinReader reader;
+  int retval = scanf_core::scanf_main(&reader, format, args);
+  // This is done to avoid including stdio.h in the internals. On most systems
+  // EOF is -1, so this will be transformed into just "return retval".
+  return (retval == -1) ? EOF : retval;
+}
+
+} // namespace LIBC_NAMESPACE_DECL

libc/src/stdio/baremetal/scanf_internal.h

@@ -0,0 +1,30 @@
+//===-- Internal implementation header of scanf -----------------*- 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/__support/OSUtil/io.h"
+#include "src/__support/macros/config.h"
+#include "src/stdio/scanf_core/reader.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace scanf_core {
+
+struct StdinReader : public Reader<StdinReader> {
+  LIBC_INLINE char getc() {
+    char buf[1];
+    auto result = read_from_stdin(buf, sizeof(buf));
+    if (result <= 0)
+      return EOF;
+    return buf[0];
+  }
+  LIBC_INLINE void ungetc(int) {}
+};
+
+} // namespace scanf_core
+
+} // namespace LIBC_NAMESPACE_DECL

libc/src/stdio/baremetal/vscanf.cpp

@@ -0,0 +1,36 @@
+//===-- Implementation of vscanf --------------------------------*- 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/vscanf.h"
+
+#include "hdr/stdio_macros.h"
+#include "src/__support/OSUtil/io.h"
+#include "src/__support/arg_list.h"
+#include "src/__support/macros/config.h"
+#include "src/stdio/baremetal/scanf_internal.h"
+#include "src/stdio/scanf_core/scanf_main.h"
+
+#include <stdarg.h>
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, vscanf,
+                   (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.
+  va_end(vlist);
+
+  scanf_core::StdinReader reader;
+  int retval = scanf_core::scanf_main(&reader, format, args);
+  // This is done to avoid including stdio.h in the internals. On most systems
+  // EOF is -1, so this will be transformed into just "return retval".
+  return (retval == -1) ? EOF : retval;
+}
+
+} // namespace LIBC_NAMESPACE_DECL

libc/src/stdio/generic/CMakeLists.txt

@@ -425,6 +425,60 @@ add_entrypoint_object(
     ${fprintf_deps}
 )
 
+list(APPEND scanf_deps
+      libc.src.__support.arg_list
+      libc.src.stdio.scanf_core.vfscanf_internal
+      libc.hdr.types.FILE
+)
+
+if(LLVM_LIBC_FULL_BUILD AND NOT LIBC_TARGET_OS_IS_GPU)
+  list(APPEND scanf_deps
+      libc.src.__support.File.file
+      libc.src.__support.File.platform_file
+      libc.src.__support.File.platform_stdin
+  )
+endif()
+
+add_entrypoint_object(
+  fscanf
+  SRCS
+    fscanf.cpp
+  HDRS
+    ../fscanf.h
+  DEPENDS
+    ${scanf_deps}
+)
+
+add_entrypoint_object(
+  vfscanf
+  SRCS
+    vfscanf.cpp
+  HDRS
+    ../vfscanf.h
+  DEPENDS
+    ${scanf_deps}
+)
+
+add_entrypoint_object(
+  scanf
+  SRCS
+    scanf.cpp
+  HDRS
+    ../scanf.h
+  DEPENDS
+    ${scanf_deps}
+)
+
+add_entrypoint_object(
+  vscanf
+  SRCS
+    vscanf.cpp
+  HDRS
+    ../vscanf.h
+  DEPENDS
+    ${scanf_deps}
+)
+
 add_entrypoint_object(
   fgets
   SRCS