[safestack] Turn the OS X SafeStack runtime into a dynamic library

[kubamracek]

Summary

On OS X, the are two huge drawbacks to having a static library (.a) as a runtime:

1. Interceptors don't work -- and SafeStack relies on intercepting pthread_create.
2. Having multiple instrumented modules (frameworks, dylibs, bundles) in a single process is problematic and requires special care when building each module.

Let's make the runtime a dynamic library, just like the other sanitizers (ASan, TSan).

[samsonov]

tools/clang/lib/Driver/Tools.cpp

6963

How do you address this now?

[kubamracek]

tools/clang/lib/Driver/Tools.cpp

6963

We link against the SafeStack dylib (we depend on it), so its constructors will be run before any constructors of the instrumented module. This is only an issue with a static library, where the __safestack_init constructor is in the same module as instrumented code.

[samsonov]

I'm in favor of this change, but will let Peter or Evgeniy sign this off.

[eugenis]

I'm fine with this.

[Eugene.Zelenko]

Looks like patch was not committed.

projects/compiler-rt/lib/safestack/CMakeLists.txt

 add_custom_target(safestack)
 
 set(SAFESTACK_SOURCES safestack.cc)
 
 include_directories(..)
 
 set(SAFESTACK_CFLAGS ${SANITIZER_COMMON_CFLAGS})
 
 if(APPLE)
   # Build universal binary on APPLE.
   add_compiler_rt_runtime(clang_rt.safestack
-    STATIC
+    SHARED
     OS osx
     ARCHS ${SAFESTACK_SUPPORTED_ARCH}
     SOURCES ${SAFESTACK_SOURCES}
             $<TARGET_OBJECTS:RTInterception.osx>
             $<TARGET_OBJECTS:RTSanitizerCommon.osx>
-            $<TARGET_OBJECTS:RTSanitizerCommonNoLibc.osx>
+            $<TARGET_OBJECTS:RTSanitizerCommonLibc.osx>
     CFLAGS ${SAFESTACK_CFLAGS}
     PARENT_TARGET safestack)
 else()
   # Otherwise, build separate libraries for each target.
   foreach(arch ${SAFESTACK_SUPPORTED_ARCH})
     add_compiler_rt_runtime(clang_rt.safestack
       STATIC
       ARCHS ${arch}
       SOURCES ${SAFESTACK_SOURCES}
               $<TARGET_OBJECTS:RTInterception.${arch}>
               $<TARGET_OBJECTS:RTSanitizerCommon.${arch}>
               $<TARGET_OBJECTS:RTSanitizerCommonNoLibc.${arch}>
       CFLAGS ${SAFESTACK_CFLAGS}
       PARENT_TARGET safestack)
   endforeach()
 endif()

tools/clang/lib/Driver/ToolChains.cpp

void DarwinClang::AddLinkRuntimeLibArgs(const ArgList &Args,
 
   const SanitizerArgs &Sanitize = getSanitizerArgs();
   if (Sanitize.needsAsanRt())
     AddLinkSanitizerLibArgs(Args, CmdArgs, "asan");
   if (Sanitize.needsUbsanRt())
     AddLinkSanitizerLibArgs(Args, CmdArgs, "ubsan");
   if (Sanitize.needsTsanRt())
     AddLinkSanitizerLibArgs(Args, CmdArgs, "tsan");
+  if (Sanitize.needsSafeStackRt())
+    AddLinkSanitizerLibArgs(Args, CmdArgs, "safestack");
 
   // Otherwise link libSystem, then the dynamic runtime library, and finally any
   // target specific static runtime library.
   CmdArgs.push_back("-lSystem");
 
   // Select the dynamic runtime library and the target specific static library.
   if (isTargetWatchOSBased()) {
     // We currently always need a static runtime library for watchOS.

tools/clang/lib/Driver/Tools.cpp

if (Args.hasArg(options::OPT_ObjC) || Args.hasArg(options::OPT_ObjCXX))
     CmdArgs.push_back("-ObjC");
 
   CmdArgs.push_back("-o");
   CmdArgs.push_back(Output.getFilename());
 
   if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles))
     getMachOToolChain().addStartObjectFileArgs(Args, CmdArgs);
 
-  // SafeStack requires its own runtime libraries
-  // These libraries should be linked first, to make sure the
-  // __safestack_init constructor executes before everything else
-  if (getToolChain().getSanitizerArgs().needsSafeStackRt()) {
-    getMachOToolChain().AddLinkRuntimeLib(Args, CmdArgs,
-                                          "libclang_rt.safestack_osx.a",
-                                          /*AlwaysLink=*/true);
-  }
-
   Args.AddAllArgs(CmdArgs, options::OPT_L);
 
   AddLinkerInputs(getToolChain(), Inputs, Args, CmdArgs);
   // Build the input file for -filelist (list of linker input files) in case we
   // need it later
   for (const auto &II : Inputs) {
     if (!II.isFilename()) {
       // This is a linker input argument.