Bug 1592250 - Disable libFuzzer instrumentation in TSan builds. r=dmajor

Differential Revision: https://phabricator.services.mozilla.com/D50922

--HG--
extra : moz-landing-system : lando

build/moz.configure/toolchain.configure

@@ -2340,8 +2340,17 @@ add_old_configure_assignment('FUZZING_INTERFACES', enable_fuzzing_interfaces)
 
 @depends(c_compiler.try_compile(flags=['-fsanitize=fuzzer-no-link'],
          when=enable_fuzzing,
-         check_msg='whether the C compiler supports -fsanitize=fuzzer-no-link'))
-def libfuzzer_flags(value):
+         check_msg='whether the C compiler supports -fsanitize=fuzzer-no-link'), tsan)
+def libfuzzer_flags(value, tsan):
+    if tsan:
+        # With ThreadSanitizer, we should not use any libFuzzer instrumentation because
+        # it is incompatible (e.g. there are races on global sanitizer coverage counters).
+        # Instead we use an empty set of flags here but still build the fuzzing targets.
+        # With this setup, we can still run files through these targets in TSan builds,
+        # e.g. those obtained from regular fuzzing.
+        # This code can be removed once libFuzzer has been made compatible with TSan.
+        return namespace(no_link_flag_supported=False, use_flags=[])
+
     if value:
         no_link_flag_supported = True
         # recommended for (and only supported by) clang >= 6

config/makefiles/rust.mk

@@ -67,6 +67,7 @@ endif
 
 rustflags_sancov =
 ifdef FUZZING_INTERFACES
+ifndef MOZ_TSAN
 # These options should match what is implicitly enabled for `clang -fsanitize=fuzzer`
 #   here: https://github.com/llvm/llvm-project/blob/release/8.x/clang/lib/Driver/SanitizerArgs.cpp#L354
 #
@@ -74,8 +75,11 @@ ifdef FUZZING_INTERFACES
 #  -sanitizer-coverage-level=4                   Enable coverage for all blocks, critical edges, and indirect calls.
 #  -sanitizer-coverage-trace-compares            Tracing of CMP and similar instructions.
 #  -sanitizer-coverage-pc-table                  Create a static PC table.
+#
+# In TSan builds, we must not pass any of these, because sanitizer coverage is incompatible with TSan.
 rustflags_sancov += -Cpasses=sancov -Cllvm-args=-sanitizer-coverage-inline-8bit-counters -Cllvm-args=-sanitizer-coverage-level=4 -Cllvm-args=-sanitizer-coverage-trace-compares -Cllvm-args=-sanitizer-coverage-pc-table
 endif
+endif
 
 rustflags_override = $(MOZ_RUST_DEFAULT_FLAGS) $(rustflags_neon)