[compiler-rt] Explicitly enable C extensions for profile

[tambry]

The profiling code requires GNU extensions as it uses functions such as getpagesize(), fdopen(), etc.

The problem manifests when the compiler is built to not default to the extensions mode, e.g. custom config with -std=c2x. CMake didn't support this scenario very well, but it's been fixed by CMP0128. Set the policy to NEW as we now conform to it.

[llvmbot]

@llvm/pr-subscribers-pgo

Author: Raul Tambre (tambry)

Changes

The profiling code requires GNU extensions as it uses functions such as getpagesize(), fdopen(), etc.

The problem manifests when the compiler is built to not default to the extensions mode, e.g. custom config with -std=c2x. CMake didn't support this scenario very well, but it's been fixed by CMP0128. Set the policy to NEW as we now conform to it.

---

Full diff: https://github.com/llvm/llvm-project/pull/110555.diff

3 Files Affected:

• (modified) compiler-rt/CMakeLists.txt (+5)
• (modified) compiler-rt/cmake/Modules/AddCompilerRT.cmake (+7-2)
• (modified) compiler-rt/lib/profile/CMakeLists.txt (+4-2)

diff --git a/compiler-rt/CMakeLists.txt b/compiler-rt/CMakeLists.txt
index deb6994f481854..1c24b520da985d 100644
--- a/compiler-rt/CMakeLists.txt
+++ b/compiler-rt/CMakeLists.txt
@@ -12,6 +12,11 @@ endif()
 include(${LLVM_COMMON_CMAKE_UTILS}/Modules/CMakePolicy.cmake
   NO_POLICY_SCOPE)
 
+# TODO(CMake 3.22): remove
+if(POLICY CMP0128)
+  cmake_policy(SET CMP0128 NEW)
+endif()
+
 # Check if compiler-rt is built as a standalone project.
 if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR OR COMPILER_RT_STANDALONE_BUILD)
   project(CompilerRT C CXX ASM)
diff --git a/compiler-rt/cmake/Modules/AddCompilerRT.cmake b/compiler-rt/cmake/Modules/AddCompilerRT.cmake
index 6962b733733a6a..e3d81d241b1054 100644
--- a/compiler-rt/cmake/Modules/AddCompilerRT.cmake
+++ b/compiler-rt/cmake/Modules/AddCompilerRT.cmake
@@ -161,7 +161,8 @@ endmacro()
 #                         LINK_LIBS <linked libraries> (only for shared library)
 #                         OBJECT_LIBS <object libraries to use as sources>
 #                         PARENT_TARGET <convenience parent target>
-#                         ADDITIONAL_HEADERS <header files>)
+#                         ADDITIONAL_HEADERS <header files>
+#                         EXTENSIONS <boolean>)
 function(add_compiler_rt_runtime name type)
   if(NOT type MATCHES "^(OBJECT|STATIC|SHARED|MODULE)$")
     message(FATAL_ERROR
@@ -171,7 +172,7 @@ function(add_compiler_rt_runtime name type)
   cmake_parse_arguments(LIB
     ""
     "PARENT_TARGET"
-    "OS;ARCHS;SOURCES;CFLAGS;LINK_FLAGS;DEFS;DEPS;LINK_LIBS;OBJECT_LIBS;ADDITIONAL_HEADERS"
+    "OS;ARCHS;SOURCES;CFLAGS;LINK_FLAGS;DEFS;DEPS;LINK_LIBS;OBJECT_LIBS;ADDITIONAL_HEADERS;EXTENSIONS"
     ${ARGN})
   set(libnames)
   # Until we support this some other way, build compiler-rt runtime without LTO
@@ -435,6 +436,10 @@ function(add_compiler_rt_runtime name type)
     if(type STREQUAL "SHARED")
       rt_externalize_debuginfo(${libname})
     endif()
+
+    if(DEFINED LIB_EXTENSIONS)
+      set_target_properties(${libname} PROPERTIES C_EXTENSIONS ${LIB_EXTENSIONS})
+    endif()
   endforeach()
   if(LIB_PARENT_TARGET)
     add_dependencies(${LIB_PARENT_TARGET} ${libnames})
diff --git a/compiler-rt/lib/profile/CMakeLists.txt b/compiler-rt/lib/profile/CMakeLists.txt
index ef23492514898b..26178412967201 100644
--- a/compiler-rt/lib/profile/CMakeLists.txt
+++ b/compiler-rt/lib/profile/CMakeLists.txt
@@ -138,7 +138,8 @@ if(APPLE)
     CFLAGS ${EXTRA_FLAGS}
     SOURCES ${PROFILE_SOURCES}
     ADDITIONAL_HEADERS ${PROFILE_HEADERS}
-    PARENT_TARGET profile)
+    PARENT_TARGET profile
+    EXTENSIONS ON)
 else()
   add_compiler_rt_runtime(clang_rt.profile
     STATIC
@@ -146,5 +147,6 @@ else()
     CFLAGS ${EXTRA_FLAGS}
     SOURCES ${PROFILE_SOURCES}
     ADDITIONAL_HEADERS ${PROFILE_HEADERS}
-    PARENT_TARGET profile)
+    PARENT_TARGET profile
+    EXTENSIONS ON)
 endif()

[mstorsjo]

What happens here, if running on a version of CMake that doesn't support the new policy and then probably doesn't support the <LANG>_EXTENSIONS target property?

[tambry]

1. C_EXTENSIONS has been supported since CMake 3.1. LLVM requires 3.20.
2. If CMP0128 isn't supported then the behaviour remains the same. Compilers with extensions off by default won't have them enabled and won't be able to compile the code. No other relevant changes for LLVM.

CMP0128 is basically a bugfix (I implemented it).
But since there's code in the wild depending on the bugs it's a policy. For example some projects came to rely on <LANG>_EXTENSIONS=OFF actually not disabling extensions in some cases.

[mstorsjo]

Ah, I see - thanks for the additional explanations!

[mstorsjo]

I think these changes look good.

(Do you have commit access, or do you need someone to merge it for you?)

[tambry]

Thanks for the quick review!
Not contributing too often anymore, but enough to maintain commit access. 🙂