[sanitizer] Disable -ffunction-sections.

It breaks when a binary is linked with --gc-sections: parts of sanitizer
interface get thrown away and inaccessible from dlopen-ed libs.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@200683 91177308-0d34-0410-b5e6-96231b3b80d8

Author: eugenis

CMakeLists.txt

@@ -142,6 +142,7 @@ if (NOT MSVC)
     -fno-stack-protector
     -Wno-gnu  # Variadic macros with 0 arguments for ...
     -fvisibility=hidden
+    -fno-function-sections
     )
   if (NOT COMPILER_RT_DEBUG)
     list(APPEND SANITIZER_COMMON_CFLAGS -O3)

lib/asan/lit_tests/TestCases/Linux/function-sections-are-bad.cc

@@ -0,0 +1,39 @@
+// Check that --gc-sections does not throw away (or localize) parts of sanitizer
+// interface.
+// RUN: %clang_asan -m64 %s -Wl,--gc-sections -o %t
+// RUN: %clang_asan -m64 %s -DBUILD_SO -fPIC -o %t-so.so -shared
+// RUN: %t 2>&1
+
+#ifndef BUILD_SO
+#include <assert.h>
+#include <dlfcn.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+int main(int argc, char *argv[]) {
+  char path[4096];
+  snprintf(path, sizeof(path), "%s-so.so", argv[0]);
+
+  void *handle = dlopen(path, RTLD_LAZY);
+  if (!handle) fprintf(stderr, "%s\n", dlerror());
+  assert(handle != 0);
+
+  typedef void (*F)();
+  F f = (F)dlsym(handle, "call_rtl_from_dso");
+  printf("%s\n", dlerror());
+  assert(dlerror() == 0);
+  f();
+  
+  dlclose(handle);
+  return 0;
+}
+
+#else // BUILD_SO
+
+#include <sanitizer/msan_interface.h>
+extern "C" void call_rtl_from_dso() {
+  volatile int32_t x;
+  volatile int32_t y = __sanitizer_unaligned_load32((void *)&x);
+}
+
+#endif // BUILD_SO