Fix santizers on MacOS that require dylibs in the LLVM toolchain. (ba…

…zel-contrib#250)

Add dylibs to the `lib` target so that santizers work properly on MacOS.

Resolves bazel-contrib#192.

---------

Co-authored-by: Siddhartha Bagaria <starsid@gmail.com>

toolchain/BUILD.llvm_repo

@@ -58,6 +58,7 @@ filegroup(
         [
             "lib/**/lib*.a",
             "lib/clang/*/lib/**/*.a",
+            "lib/clang/*/lib/**/*.dylib",
             # clang_rt.*.o supply crtbegin and crtend sections.
             "lib/**/clang_rt.*.o",
         ],
@@ -67,9 +68,9 @@ filegroup(
             "lib/liblld*.a",
         ],
     ),
-    # Do not include the .dylib files in the linker sandbox because they will
-    # not be available at runtime. Any library linked from the toolchain should
-    # be linked statically.
+    # Include the .dylib files in the linker sandbox even though they will
+    # not be available at runtime to allow sanitizers to work locally.
+    # Any library linked from the toolchain to be released should be linked statically.
 )
 
 filegroup(

toolchain/cc_toolchain_config.bzl

@@ -196,32 +196,22 @@ def cc_toolchain_config(
                 "-ldl",
             ])
         else:
-            # The only known mechanism to static link libraries in ld64 is to
-            # not have the corresponding .dylib files in the library search
-            # path. The link time sandbox does not include the .dylib files, so
-            # anything we pick up from the toolchain should be statically
-            # linked. However, several system libraries on macOS dynamically
-            # link libc++ and libc++abi, so static linking them becomes a problem.
-            # We need to ensure that they are dynamic linked from the system
-            # sysroot and not static linked from the toolchain, so explicitly
-            # have the sysroot directory on the search path and then add the
-            # toolchain directory back after we are done.
+            # Several system libraries on macOS dynamically link libc++ and
+            # libc++abi, so static linking them becomes a problem. We need to
+            # ensure that they are dynamic linked from the system sysroot and
+            # not static linked from the toolchain, so explicitly have the
+            # sysroot directory on the search path and then add the toolchain
+            # directory back after we are done.
             link_flags.extend([
                 "-L{}/usr/lib".format(compiler_configuration["sysroot_path"]),
                 "-lc++",
                 "-lc++abi",
-            ])
-
-            # Let's provide the path to the toolchain library directory
-            # explicitly as part of the search path to make it easy for a user
-            # to pick up something. This also makes the behavior consistent with
-            # targets when a user explicitly depends on something like
-            # libomp.dylib, which adds this directory to the search path, and would
-            # (unintentionally) lead to static linking of libraries from the
-            # toolchain.
-            link_flags.extend([
+                "-Bstatic",
+                "-lunwind",
+                "-Bdynamic",
                 "-L{}lib".format(toolchain_path_prefix),
             ])
+
     elif stdlib == "libc++":
         cxx_flags = [
             "-std=" + cxx_standard,