6 files changed, 87 insertions, 2 deletions
diff --git a/libc/utils/CMakeLists.txt b/libc/utils/CMakeLists.txt
index ec1308927bf9..a55182065d20 100644
--- a/libc/utils/CMakeLists.txt
+++ b/libc/utils/CMakeLists.txt
@@ -4,4 +4,5 @@ add_subdirectory(LibcTableGenUtil)
 add_subdirectory(HdrGen)
 add_subdirectory(MPFRWrapper)
 add_subdirectory(testutils)
+add_subdirectory(tools)
 add_subdirectory(UnitTest)
diff --git a/libc/utils/LibcTableGenUtil/APIIndexer.cpp b/libc/utils/LibcTableGenUtil/APIIndexer.cpp
index 6ef9a6576b87..16aef5880bff 100644
--- a/libc/utils/LibcTableGenUtil/APIIndexer.cpp
+++ b/libc/utils/LibcTableGenUtil/APIIndexer.cpp
@@ -97,8 +97,9 @@ void APIIndexer::indexStandardSpecDef(llvm::Record *StandardSpec) {
 
       auto FunctionSpecList = HeaderSpec->getValueAsListOfDefs("Functions");
       for (llvm::Record *FunctionSpec : FunctionSpecList) {
-        FunctionSpecMap[std::string(FunctionSpec->getValueAsString("Name"))] =
-            FunctionSpec;
+        auto FunctionName = std::string(FunctionSpec->getValueAsString("Name"));
+        FunctionSpecMap[FunctionName] = FunctionSpec;
+        FunctionToHeaderMap[FunctionName] = std::string(Header);
       }
 
       auto EnumerationSpecList =
diff --git a/libc/utils/LibcTableGenUtil/APIIndexer.h b/libc/utils/LibcTableGenUtil/APIIndexer.h
index 8fa87113610e..7b4d62a38c61 100644
--- a/libc/utils/LibcTableGenUtil/APIIndexer.h
+++ b/libc/utils/LibcTableGenUtil/APIIndexer.h
@@ -65,6 +65,8 @@ public:
   NameToRecordMapping MacroDefsMap;
   NameToRecordMapping TypeDeclsMap;
 
+  std::unordered_map<std::string, std::string> FunctionToHeaderMap;
+
   NameSet Structs;
   NameSet Enumerations;
   NameSet Functions;
diff --git a/libc/utils/tools/CMakeLists.txt b/libc/utils/tools/CMakeLists.txt
new file mode 100644
index 000000000000..e975b7f293af
--- /dev/null
+++ b/libc/utils/tools/CMakeLists.txt
@@ -0,0 +1 @@
+add_subdirectory(WrapperGen)
diff --git a/libc/utils/tools/WrapperGen/CMakeLists.txt b/libc/utils/tools/WrapperGen/CMakeLists.txt
new file mode 100644
index 000000000000..fe8ffcce94a5
--- /dev/null
+++ b/libc/utils/tools/WrapperGen/CMakeLists.txt
@@ -0,0 +1,8 @@
+set(LLVM_LINK_COMPONENTS Support)
+
+add_tablegen(libc-wrappergen llvm-libc
+  Main.cpp
+)
+
+target_include_directories(libc-wrappergen PRIVATE ${LIBC_SOURCE_DIR})
+target_link_libraries(libc-wrappergen PRIVATE LibcTableGenUtil)
diff --git a/libc/utils/tools/WrapperGen/Main.cpp b/libc/utils/tools/WrapperGen/Main.cpp
new file mode 100644
index 000000000000..ae606d1b66fa
--- /dev/null
+++ b/libc/utils/tools/WrapperGen/Main.cpp
@@ -0,0 +1,72 @@
+//===-- "main" function of libc-wrappergen --------------------------------===//
+//
+// 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 "utils/LibcTableGenUtil/APIIndexer.h"
+
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/TableGen/Error.h"
+#include "llvm/TableGen/Main.h"
+
+#include <sstream>
+#include <string>
+
+llvm::cl::opt<std::string>
+    FunctionName("name", llvm::cl::desc("Name of the function to be wrapped."),
+                 llvm::cl::value_desc("<function name>"), llvm::cl::Required);
+
+static bool WrapperGenMain(llvm::raw_ostream &OS, llvm::RecordKeeper &Records) {
+  llvm_libc::APIIndexer Indexer(Records);
+  auto Iter = Indexer.FunctionSpecMap.find(FunctionName);
+  if (Iter == Indexer.FunctionSpecMap.end()) {
+    llvm::PrintFatalError("Function '" + FunctionName +
+                          "' not found in any standard spec.");
+  }
+
+  // To avoid all confusion, we include the implementation header using the
+  // full path (relative the libc directory.)
+  std::string Header = Indexer.FunctionToHeaderMap[FunctionName];
+  auto RelPath = llvm::StringRef(Header).drop_back(2); // Drop the ".h" suffix.
+  OS << "#include \"src/" << RelPath << "/" << FunctionName << ".h\"\n";
+
+  auto &NameSpecPair = *Iter;
+  llvm::Record *FunctionSpec = NameSpecPair.second;
+  llvm::Record *RetValSpec = FunctionSpec->getValueAsDef("Return");
+  llvm::Record *ReturnType = RetValSpec->getValueAsDef("ReturnType");
+  OS << "extern \"C\" " << Indexer.getTypeAsString(ReturnType) << " "
+     << FunctionName << "(";
+
+  auto ArgsList = FunctionSpec->getValueAsListOfDefs("Args");
+  std::stringstream CallArgs;
+  std::string ArgPrefix("__arg");
+  for (size_t i = 0; i < ArgsList.size(); ++i) {
+    llvm::Record *ArgType = ArgsList[i]->getValueAsDef("ArgType");
+    auto TypeName = Indexer.getTypeAsString(ArgType);
+    OS << TypeName << " " << ArgPrefix << i;
+    CallArgs << ArgPrefix << i;
+    if (i < ArgsList.size() - 1) {
+      OS << ", ";
+      CallArgs << ", ";
+    }
+  }
+
+  // TODO: Arg types of the C++ implementation functions need not
+  // match the standard types. Either handle such differences here, or
+  // avoid such a thing in the implementations.
+  OS << ") {\n"
+     << "  return __llvm_libc::" << FunctionName << "(" << CallArgs.str()
+     << ");\n"
+     << "}\n";
+
+  return false;
+}
+
+int main(int argc, char *argv[]) {
+  llvm::cl::ParseCommandLineOptions(argc, argv);
+  return TableGenMain(argv[0], WrapperGenMain);
+}