[libc-commits] [libc] [libc] Fix warning on 'extern "C" int main' in test suite (PR #102973)

[Joseph Huber via libc-commits]

https://github.com/jhuber6 created https://github.com/llvm/llvm-project/pull/102973

Summary:
According to the C++ standard, The main function shall not be declared
with a linkage-specification. after some changes in
https://github.com/llvm/llvm-project/pull/101853 this started emitting
warnings when building / testing the C library. This source file is
shared with the overlay tests as well as the full build tests. The full
build tests are compiled with `-ffreestanding`, as are all the startup /
integration files. The standard says freestanding environment are all
implementation defined, so this is valid in those cases. This patch
simply prevents adding the linkage when we are compiling unit tests,
which are hosted. This is a continuation on
https://github.com/llvm/llvm-project/pull/102825.


>From eb361775c7910481a22a3770c65ecc49f500880f Mon Sep 17 00:00:00 2001
From: Joseph Huber <huberjn at outlook.com>
Date: Mon, 12 Aug 2024 15:36:11 -0500
Subject: [PATCH] [libc] Fix warning on 'extern "C" int main' in test suite

Summary:
According to the C++ standard, The main function shall not be declared
with a linkage-specification. after some changes in
https://github.com/llvm/llvm-project/pull/101853 this started emitting
warnings when building / testing the C library. This source file is
shared with the overlay tests as well as the full build tests. The full
build tests are compiled with `-ffreestanding`, as are all the startup /
integration files. The standard says freestanding environment are all
implementation defined, so this is valid in those cases. This patch
simply prevents adding the linkage when we are compiling unit tests,
which are hosted. This is a continuation on
https://github.com/llvm/llvm-project/pull/102825.
---
 libc/test/UnitTest/CMakeLists.txt   |  1 +
 libc/test/UnitTest/LibcTestMain.cpp | 10 +++++++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/libc/test/UnitTest/CMakeLists.txt b/libc/test/UnitTest/CMakeLists.txt
index 6427b861580777..9e9fc8153769cf 100644
--- a/libc/test/UnitTest/CMakeLists.txt
+++ b/libc/test/UnitTest/CMakeLists.txt
@@ -32,6 +32,7 @@ function(add_unittest_framework_library name)
   _get_hermetic_test_compile_options(compile_options -nostdinc++)
   target_include_directories(${name}.hermetic PRIVATE ${LIBC_BUILD_DIR}/include)
   target_compile_options(${name}.hermetic PRIVATE ${compile_options})
+  target_compile_definitions(${name}.hermetic PRIVATE LIBC_HERMETIC_TEST)
 
   if(TEST_LIB_DEPENDS)
     foreach(dep IN ITEMS ${TEST_LIB_DEPENDS})
diff --git a/libc/test/UnitTest/LibcTestMain.cpp b/libc/test/UnitTest/LibcTestMain.cpp
index 94536e97164686..ece5639769d215 100644
--- a/libc/test/UnitTest/LibcTestMain.cpp
+++ b/libc/test/UnitTest/LibcTestMain.cpp
@@ -43,7 +43,15 @@ TestOptions parseOptions(int argc, char **argv) {
 
 } // anonymous namespace
 
-extern "C" int main(int argc, char **argv, char **envp) {
+// The C++ standard forbids declaring the main function with a linkage specifier
+// outisde of 'freestanding' mode, only define the linkage for hermetic tests.
+#ifdef LIBC_HERMETIC_TEST
+#define TEST_MAIN extern "C" int main
+#else
+#define TEST_MAIN int main
+#endif
+
+TEST_MAIN(int argc, char **argv, char **envp) {
   LIBC_NAMESPACE::testing::argc = argc;
   LIBC_NAMESPACE::testing::argv = argv;
   LIBC_NAMESPACE::testing::envp = envp;