[scudo] Fuchsia minimal shared runtime

[cryptoad]

Summary

Fuchsia requires its Scudo shared runtime to not be C++ dependant. Since they
don't use UBSan in conjunction with Scudo, we can just remove the runtime,
and add the extra nostdinc++ and nostdlib++ flags. No need for Coverage
either. This allows to keep things going while working on additional splits
of sanitizer_commong and a more minimal runtime.

[cryptoad]

I am actually unsure about the FUCHSIA ifs, it is be used on the builtins but I can't see it defined in compiler-rt.

[cryptoad]

Finally have a working Fuchsia toolchain, so I don't have to ask @flowerhack to test my stuff all the time.
I am going to make sure this works as intended and comment back here.

[phosek]

In D44791#1045855, @cryptoad wrote:

I am actually unsure about the FUCHSIA ifs, it is be used on the builtins but I can't see it defined in compiler-rt.

FUCHSIA is defined by CMake when the CMAKE_SYSTEM_NAME is set to Fuchsia.

[cryptoad]

Finally got the toolchain working.

A few changes: -nostdlib++ is a clang flag, and as of now Fuchsia requires
libunwind to be explicitely linked (it was in SANITIZER_CXX_ABI_LIBRARY
before). It will go away when I am done splitting the stacktraces from
RTSanitizerCommon.

Resulting binary for Fuchsia is no longer C++ dependent (UBSan is gone - for
now), but still has ~512kB of unneeded BSS usage due to the internal allocator
used by the symbolizer. This will also go away when the split it done.

[phosek]

lib/scudo/CMakeLists.txt

24

You could add RTSanitizerCommonCoverage, RTUbsan, RTUbsan_cxx to a variable (e.g. ${SCUDO_EXTRA_OBJECT_LIBS}) and ${SANITIZER_CXX_ABI_LIBRARY} to ${SCUDO_DYNAMIC_LIBS} in the else branch and then you don't need the two different branches for add_compiler_rt_runtime(clang_rt.scudo ...) below.

63–64

Is this needed? I see it being included in STATIC library for all platforms and SHARED library for everything but Fuchsia. Is that correct?

[cryptoad]

lib/scudo/CMakeLists.txt

24

Will do.

63–64

That is correct.
ubsan_init.cc makes use of __sanitizer::InitializeCoverage so everything that uses UBsan has to include coverage.
Scudo doesn't need coverage or symbolizer, which are intertwined within RTSanitizerCommon, so I am in the process of splitting them both in order to have a thin runtime that isn't pulling in extraneous dependencies from sanitizer_common.

[cryptoad]

Addressing review comments.

[cryptoad]

Typo.

[phosek]

lib/scudo/CMakeLists.txt

26

I think -nostdlib++ should be in SCUDO_DYNAMIC_LINK_FLAGS as -Wl,-nostdlib++ (unless add_compiler_rt_runtime already adds all CFLAGS to LDFLAGS automatically).

[cryptoad]

lib/scudo/CMakeLists.txt

26

I tried that initially but lld (unlike ld) doesn't seem to support it:
ld.lld: error: unknown argument: -nostdlib++
Documentation I could find seems to indicate it as a clang flag (https://clang.llvm.org/docs/ClangCommandLineReference.html)

[phosek]

lib/scudo/CMakeLists.txt

26

Oh my bad, it should be -nostdlib++ since that flag is actually processed by Clang driver, not by LLD.

26

However, it should still be in SCUDO_DYNAMIC_LINK_FLAGS rather than SCUDO_FLAGS.

[cryptoad]

Moving -nostdlib++ into the dynamic link flags.

[phosek]

LGTM

lib/scudo/CMakeLists.txt

 add_compiler_rt_component(scudo)
 
 include_directories(..)
 
 set(SCUDO_CFLAGS ${SANITIZER_COMMON_CFLAGS})
 # SANITIZER_COMMON_CFLAGS include -fno-builtin, but we actually want builtins!
-list(APPEND SCUDO_CFLAGS -fbuiltin)
+list(APPEND SCUDO_CFLAGS -fbuiltin -ffunction-sections -fdata-sections)
 append_rtti_flag(OFF SCUDO_CFLAGS)
 
-set(SCUDO_DYNAMIC_LINK_FLAGS ${SANITIZER_COMMON_LINK_FLAGS})
+set(SCUDO_DYNAMIC_LIBS ${SANITIZER_COMMON_LINK_LIBS})
+append_list_if(COMPILER_RT_HAS_LIBDL dl SCUDO_DYNAMIC_LIBS)
+append_list_if(COMPILER_RT_HAS_LIBRT rt SCUDO_DYNAMIC_LIBS)
+append_list_if(COMPILER_RT_HAS_LIBPTHREAD pthread SCUDO_DYNAMIC_LIBS)
+append_list_if(COMPILER_RT_HAS_LIBLOG log SCUDO_DYNAMIC_LIBS)
 
+set(SCUDO_DYNAMIC_LINK_FLAGS ${SANITIZER_COMMON_LINK_FLAGS})
 # Use gc-sections by default to avoid unused code being pulled in.
-list(APPEND SCUDO_CFLAGS -ffunction-sections -fdata-sections)
 list(APPEND SCUDO_DYNAMIC_LINK_FLAGS -Wl,--gc-sections)
 
+set(SCUDO_OBJECT_LIBS
+  RTSanitizerCommonNoTermination
+  RTSanitizerCommonLibc
+  RTInterception)
+
+if (FUCHSIA)
+  list(APPEND SCUDO_CFLAGS -nostdinc++)
+  list(APPEND SCUDO_DYNAMIC_LINK_FLAGS -nostdlib++)
+  # TODO(kostyak): remove when stacktraces are split off of RTSanitizerCommon
+  list(APPEND SCUDO_DYNAMIC_LIBS unwind_shared)
+else()
+  list(APPEND SCUDO_OBJECT_LIBS RTSanitizerCommonCoverage RTUbsan)
+  list(APPEND SCUDO_DYNAMIC_LIBS ${SANITIZER_CXX_ABI_LIBRARY})
+endif()
+
 set(SCUDO_SOURCES
   scudo_allocator.cpp
   scudo_crc32.cpp
   scudo_flags.cpp
   scudo_malloc.cpp
   scudo_termination.cpp
   scudo_tsd_exclusive.cpp
   scudo_tsd_shared.cpp

 
 # Enable the AArch64 CRC32 feature for scudo_crc32.cpp, if available.
 # Note that it is enabled by default starting with armv8.1-a.
 if (COMPILER_RT_HAS_MCRC_FLAG)
   set_source_files_properties(scudo_crc32.cpp PROPERTIES COMPILE_FLAGS -mcrc)
 endif()
 
 if(COMPILER_RT_HAS_SCUDO)
-  set(SCUDO_DYNAMIC_LIBS ${SANITIZER_CXX_ABI_LIBRARY}
-                         ${SANITIZER_COMMON_LINK_LIBS})
-  append_list_if(COMPILER_RT_HAS_LIBDL dl SCUDO_DYNAMIC_LIBS)
-  append_list_if(COMPILER_RT_HAS_LIBRT rt SCUDO_DYNAMIC_LIBS)
-  append_list_if(COMPILER_RT_HAS_LIBPTHREAD pthread SCUDO_DYNAMIC_LIBS)
-  append_list_if(COMPILER_RT_HAS_LIBLOG log SCUDO_DYNAMIC_LIBS)
-
   add_compiler_rt_runtime(clang_rt.scudo
     STATIC
     ARCHS ${SCUDO_SUPPORTED_ARCH}
     SOURCES ${SCUDO_SOURCES}
-    OBJECT_LIBS RTSanitizerCommonNoTermination
-                RTSanitizerCommonLibc
-                RTSanitizerCommonCoverage
-                RTInterception
-                RTUbsan
+    OBJECT_LIBS ${SCUDO_OBJECT_LIBS}
     CFLAGS ${SCUDO_CFLAGS}
     PARENT_TARGET scudo)
 
   add_compiler_rt_runtime(clang_rt.scudo_cxx
     STATIC
     ARCHS ${SCUDO_SUPPORTED_ARCH}
     SOURCES ${SCUDO_CXX_SOURCES}
     OBJECT_LIBS RTUbsan_cxx
     CFLAGS ${SCUDO_CFLAGS}
     PARENT_TARGET scudo)
 
   add_compiler_rt_runtime(clang_rt.scudo
     SHARED
     ARCHS ${SCUDO_SUPPORTED_ARCH}
     SOURCES ${SCUDO_SOURCES} ${SCUDO_CXX_SOURCES}
-    OBJECT_LIBS RTSanitizerCommonNoTermination
-                RTSanitizerCommonLibc
-                RTSanitizerCommonCoverage
-                RTInterception
-                RTUbsan
-                RTUbsan_cxx
+    OBJECT_LIBS ${SCUDO_OBJECT_LIBS}
     CFLAGS ${SCUDO_CFLAGS}
     LINK_FLAGS ${SCUDO_DYNAMIC_LINK_FLAGS}
     LINK_LIBS ${SCUDO_DYNAMIC_LIBS}
     PARENT_TARGET scudo)
 endif()