[sanitizer] Fix for CMAKE_CXX_FLAGS update

[bcain]

Summary

Adds a cmake fix for empty CMAKE_CXX_FLAGS in gwp_asan, profile,
scudo-standalone.

[vitalybuka]

compiler-rt/lib/gwp_asan/CMakeLists.txt

42

why do we need this if?
it looks no-op for empty string anyway

[bcain]

compiler-rt/lib/gwp_asan/CMakeLists.txt

42

cmake was giving an error about REGEX if CMAKE_CXX_FLAGS is empty: something like REGEX sub-command REPLACE requires at least four arguments.

But after removing this patch and rebuilding, I cannot reproduce the failure I saw before. I must have done something invalid.

[bcain]

compiler-rt/lib/gwp_asan/CMakeLists.txt

42

Ok I have reproduced the failure. hexagon-unknown-linux-musl-clang++ is built with CLANG_DEFAULT_CXX_STDLIB="libc++". Perhaps that eliminates the need for CMAKE_CXX_FLAGS to contain -stdlib=libc++? And if it's not there (and CMAKE_CXX_FLAGS is empty), I get this failure:

CMake Error at lib/scudo/standalone/CMakeLists.txt:14 (string):
string sub-command REGEX, mode REPLACE needs at least 6 arguments total to
command.

... and for lib/profile/CMakeLists.txt:116 etc.

[vitalybuka]

compiler-rt/lib/gwp_asan/CMakeLists.txt

43

This should be enough

[bcain]

Changed to suggested fix

compiler-rt/lib/gwp_asan/CMakeLists.txt

 # allocators. Some supporting allocators (e.g. scudo standalone) cannot use any
 # parts of the C++ standard library.
 set(GWP_ASAN_CFLAGS ${SANITIZER_COMMON_CFLAGS} -fno-rtti -fno-exceptions
     -nostdinc++ -pthread -fno-omit-frame-pointer)
 append_list_if(COMPILER_RT_HAS_FPIC_FLAG -fPIC GWP_ASAN_CFLAGS)
 # append_list_if(COMPILER_RT_HAS_SANITIZER_COMMON ${SANITIZER_COMMON_CFLAGS} GWP_ASAN_CFLAGS)
 
 # Remove -stdlib= which is unused when passing -nostdinc++.
+if (NOT "${CMAKE_CXX_FLAGS}" STREQUAL "")
 string(REGEX REPLACE "-stdlib=[a-zA-Z+]*" "" CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
+endif()
 
 # Options parsing support is optional. This is an optional library that can be
 # used by an allocator to automatically parse GwpAsan options from the
 # environment variable GWP_ASAN_FLAGS, but the allocator can choose to implement
 # its own options parsing and populate the Options struct itself.
 set(GWP_ASAN_OPTIONS_PARSER_SOURCES
   optional/options_parser.cpp
 )

compiler-rt/lib/profile/CMakeLists.txt

  set(EXTRA_FLAGS
      ${EXTRA_FLAGS}
      -DCOMPILER_RT_HAS_UNAME=1)
 endif()
 
 # We don't use the C++ Standard Library here, so avoid including it by mistake.
 append_list_if(COMPILER_RT_HAS_NOSTDINCXX_FLAG -nostdinc++ EXTRA_FLAGS)
 # XRay uses C++ standard library headers.
+if (NOT "${CMAKE_CXX_FLAGS}" STREQUAL "")
 string(REGEX REPLACE "-stdlib=[a-zA-Z+]*" "" CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
+endif()
+
 
 # This appears to be a C-only warning banning the use of locals in aggregate
 # initializers. All other compilers accept this, though.
 # nonstandard extension used : 'identifier' : cannot be initialized using address of automatic variable
 append_list_if(COMPILER_RT_HAS_WD4221_FLAG /wd4221 EXTRA_FLAGS)
 
 if(APPLE)
   add_compiler_rt_runtime(clang_rt.profile

compiler-rt/lib/scudo/standalone/CMakeLists.txt

 add_compiler_rt_component(scudo_standalone)
 
 include_directories(../.. include)
 
 set(SCUDO_CFLAGS)
 
 list(APPEND SCUDO_CFLAGS
   -Werror=conversion
   -Wall
   -g
   -nostdinc++)
 
 # Too many existing bugs, needs cleanup.
 append_list_if(COMPILER_RT_HAS_WNO_FORMAT -Wno-format SCUDO_CFLAGS)
 
 # Remove -stdlib= which is unused when passing -nostdinc++.
+if (NOT "${CMAKE_CXX_FLAGS}" STREQUAL "")
 string(REGEX REPLACE "-stdlib=[a-zA-Z+]*" "" CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
+endif()
+
 
 append_list_if(COMPILER_RT_HAS_FVISIBILITY_HIDDEN_FLAG -fvisibility=hidden SCUDO_CFLAGS)
 
 append_list_if(COMPILER_RT_HAS_FNO_EXCEPTIONS_FLAG -fno-exceptions SCUDO_CFLAGS)
 
 append_list_if(COMPILER_RT_HAS_WNO_PEDANTIC -Wno-pedantic SCUDO_CFLAGS)
 
 # FIXME: find cleaner way to agree with GWPAsan flags