[libc] Replace -nostdlib++ flag when building with gcc and add placement new operator to HermeticTestUtils.cpp.

[lntue]

-nostdlib++ is a clang-only flag. Replacing it with -nostdlib when building with gcc.

[llvmbot]

@llvm/pr-subscribers-libc

Author: None (lntue)

Changes

-nostdlib++ is a clang-only flag. Replacing it with -nostdlib when building with gcc.

---

Full diff: https://github.com/llvm/llvm-project/pull/78906.diff

2 Files Affected:

• (modified) libc/cmake/modules/LLVMLibCTestRules.cmake (+6-2)
• (modified) libc/test/UnitTest/HermeticTestUtils.cpp (+4)

diff --git a/libc/cmake/modules/LLVMLibCTestRules.cmake b/libc/cmake/modules/LLVMLibCTestRules.cmake
index 24f543f6e4c132..211188da801524 100644
--- a/libc/cmake/modules/LLVMLibCTestRules.cmake
+++ b/libc/cmake/modules/LLVMLibCTestRules.cmake
@@ -564,8 +564,10 @@ function(add_integration_test test_name)
 
   if(LIBC_TARGET_ARCHITECTURE_IS_GPU)
     target_link_options(${fq_build_target_name} PRIVATE -nostdlib -static)
-  else()
+  elseif(CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
     target_link_options(${fq_build_target_name} PRIVATE -nolibc -nostartfiles -nostdlib++ -static)
+  else()
+    target_link_options(${fq_build_target_name} PRIVATE -nolibc -nostartfiles -nostdlib -static)
   endif()
   target_link_libraries(
     ${fq_build_target_name}
@@ -741,8 +743,10 @@ function(add_libc_hermetic_test test_name)
 
   if(LIBC_TARGET_ARCHITECTURE_IS_GPU)
     target_link_options(${fq_build_target_name} PRIVATE -nostdlib -static)
-  else()
+  elseif(CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
     target_link_options(${fq_build_target_name} PRIVATE -nolibc -nostartfiles -nostdlib++ -static)
+  else()
+    target_link_options(${fq_build_target_name} PRIVATE -nolibc -nostartfiles -nostdlib -static)
   endif()
   target_link_libraries(
     ${fq_build_target_name}
diff --git a/libc/test/UnitTest/HermeticTestUtils.cpp b/libc/test/UnitTest/HermeticTestUtils.cpp
index 68e31f478d79ab..349c182ff2379f 100644
--- a/libc/test/UnitTest/HermeticTestUtils.cpp
+++ b/libc/test/UnitTest/HermeticTestUtils.cpp
@@ -104,6 +104,8 @@ void *__dso_handle = nullptr;
 
 } // extern "C"
 
+void *operator new(unsigned long size, void *ptr) { return ptr; }
+
 void *operator new(size_t size) { return malloc(size); }
 
 void *operator new[](size_t size) { return malloc(size); }
@@ -113,3 +115,5 @@ void operator delete(void *) {
   // we just trap here to catch any such accidental usages.
   __builtin_trap();
 }
+
+void operator delete(void *ptr, size_t size) { __builtin_trap(); }

[jhuber6]

Does this work with -nostdlib on clang? If so it's probably better to be consistent.

[SchrodingerZhu]

llvm-project/libc/test/UnitTest/HermeticTestUtils.cpp

Line 26 in 37ca558

// Integration tests cannot use the SCUDO standalone allocator as SCUDO pulls

Is this still true with COMPILER_RT_BUILD_SCUDO_STANDALONE_WITH_LLVM_LIBC?

[nickdesaulniers]

gcc-13 added support for -nostdlib++. Perhaps it's worth using check_cxx_compiler_flag to check for -nostdlib++ support, then fall back to -nostdlib if not?

[SchrodingerZhu]

The change itself looks good to me. Just curious that if COMPILER_RT_BUILD_SCUDO_STANDALONE_WITH_LLVM_LIBC guarantees the compatibility.

[michaelrj-google]

overall LGTM

[michaelrj-google]

is this okay or should it call realloc?

[lntue]

This is variation (9) in the list: https://en.cppreference.com/w/cpp/memory/new/operator_new
and it is said that: "The standard library implementation performs no action and returns ptr unmodified."