[libc-commits] [libc] [libc] Enabling code coverage via Linux syscalls (PR #213271)

[Jeff Bailey via libc-commits]

================
@@ -91,6 +91,32 @@ endif()
 set(LIBC_LINK_OPTIONS_DEFAULT "" CACHE STRING "Arguments used when linking.")
 set(LIBC_TEST_LINK_OPTIONS_DEFAULT "" CACHE STRING "Common link options for all the tests.")
 
+option(LLVM_LIBC_ENABLE_COVERAGE "Build libc with coverage instrumentation" OFF)
+if(LLVM_LIBC_ENABLE_COVERAGE)
+  list(APPEND LIBC_COMPILE_OPTIONS_DEFAULT "-fprofile-instr-generate" "-fcoverage-mapping")
+  list(APPEND LIBC_TEST_COMPILE_OPTIONS_DEFAULT "-fprofile-instr-generate" "-fcoverage-mapping")
+  list(APPEND LIBC_TEST_LINK_OPTIONS_DEFAULT "-fprofile-instr-generate" "-fcoverage-mapping")
+
+  # When building with -nostdlib, the compiler does not automatically link the profiling runtime.
+  # We must explicitly query the compiler for the exact architecture-specific profile library path.
+  execute_process(
+    COMMAND ${CMAKE_CXX_COMPILER} --print-libgcc-file-name --rtlib=compiler-rt
+    OUTPUT_VARIABLE COMPILER_RT_BUILTINS
+    OUTPUT_STRIP_TRAILING_WHITESPACE
+    RESULT_VARIABLE COMPILER_RT_RETURN_CODE
+  )
+  if(COMPILER_RT_RETURN_CODE EQUAL 0)
+    string(REPLACE "builtins" "profile" COMPILER_RT_PROFILE "${COMPILER_RT_BUILTINS}")
+    if(EXISTS "${COMPILER_RT_PROFILE}")
+      list(APPEND LIBC_TEST_LINK_OPTIONS_DEFAULT "${COMPILER_RT_PROFILE}")
+    else()
+      message(WARNING "Coverage profiling runtime not found at ${COMPILER_RT_PROFILE}")
----------------
kaladron wrote:

```suggestion
      message(WARNING
              "Coverage profiling runtime not found at ${COMPILER_RT_PROFILE}")
```

https://github.com/llvm/llvm-project/pull/213271