[asan] Make ASan compatible with linker dead stripping on Linux, compiler-rt part

[eugenis]

Summary

This is the compiler-rt part of https://reviews.llvm.org/D28498

lib/asan/asan_globals.cc

 // This mirrors __asan_register_image_globals.
 void __asan_unregister_image_globals(uptr *flag) {
   if (!*flag)
     return;
   AsanApplyToGlobals(__asan_unregister_globals, flag);
   *flag = 0;
 }
 
+void __asan_register_elf_globals(uptr *flag, void *start, void *stop) {
+  if (*flag) return;
+  if (!start) return;
+  CHECK_EQ(0, ((uptr)stop - (uptr)start) % sizeof(__asan_global));
+  __asan_global *globals_start = (__asan_global*)start;
+  __asan_global *globals_stop = (__asan_global*)stop;
+  __asan_register_globals(globals_start, globals_stop - globals_start);
+  *flag = 1;
+}
+
+void __asan_unregister_elf_globals(uptr *flag, void *start, void *stop) {
+  if (!*flag) return;
+  if (!start) return;
+  CHECK_EQ(0, ((uptr)stop - (uptr)start) % sizeof(__asan_global));
+  __asan_global *globals_start = (__asan_global*)start;
+  __asan_global *globals_stop = (__asan_global*)stop;
+  __asan_unregister_globals(globals_start, globals_stop - globals_start);
+  *flag = 0;
+}
+
 // Register an array of globals.
 void __asan_register_globals(__asan_global *globals, uptr n) {
   if (!flags()->report_globals) return;
   GET_STACK_TRACE_MALLOC;
   u32 stack_id = StackDepotPut(stack);
   BlockingMutexLock lock(&mu_for_globals);
   if (!global_registration_site_vector)
     global_registration_site_vector =

lib/asan/asan_interface_internal.h

extern "C" {
   // These functions can be called on some platforms to find globals in the same
   // loaded image as `flag' and apply __asan_(un)register_globals to them,
   // filtering out redundant calls.
   SANITIZER_INTERFACE_ATTRIBUTE
   void __asan_register_image_globals(uptr *flag);
   SANITIZER_INTERFACE_ATTRIBUTE
   void __asan_unregister_image_globals(uptr *flag);
 
+  SANITIZER_INTERFACE_ATTRIBUTE
+  void __asan_register_elf_globals(uptr *flag, void *start, void *stop);
+  SANITIZER_INTERFACE_ATTRIBUTE
+  void __asan_unregister_elf_globals(uptr *flag, void *start, void *stop);
+
   // These two functions should be called by the instrumented code.
   // 'globals' is an array of structures describing 'n' globals.
   SANITIZER_INTERFACE_ATTRIBUTE
   void __asan_register_globals(__asan_global *globals, uptr n);
   SANITIZER_INTERFACE_ATTRIBUTE
   void __asan_unregister_globals(__asan_global *globals, uptr n);
 
   // These two functions should be called before and after dynamic initializers

test/asan/TestCases/Linux/globals-gc-sections-lld.cc

+// RUN: %clangxx_asan %s -o %t -Wl,--gc-sections -fuse-ld=lld -ffunction-sections -fdata-sections -mllvm -asan-globals=0
+// RUN: %clangxx_asan %s -o %t -Wl,--gc-sections -fuse-ld=lld -ffunction-sections -fdata-sections -mllvm -asan-globals=1
+
+// https://code.google.com/p/address-sanitizer/issues/detail?id=260
+
+// REQUIRES: lld
+
+int undefined();
+
+// On i386 clang adds --export-dynamic when linking with ASan, which adds all
+// non-hidden globals to GC roots.
+__attribute__((visibility("hidden"))) int (*unused)() = undefined;
+
+int main() {
+        return 0;
+}

test/asan/TestCases/Linux/globals-gc-sections.cc

-// RUN: %clangxx_asan %s -o %t -Wl,--gc-sections -ffunction-sections -mllvm -asan-globals=0
-// RUN: %clangxx_asan %s -o %t -Wl,--gc-sections -ffunction-sections -mllvm -asan-globals=1
+// RUN: %clangxx_asan %s -o %t -Wl,--gc-sections -fuse-ld=bfd -ffunction-sections -fdata-sections -mllvm -asan-globals=0
+// RUN: %clangxx_asan %s -o %t -Wl,--gc-sections -fuse-ld=bfd -ffunction-sections -fdata-sections -mllvm -asan-globals=1
 
 // https://code.google.com/p/address-sanitizer/issues/detail?id=260
-// XFAIL: *
 
 int undefined();
 
-int (*unused)() = undefined;
+// bug in ld.bfd: with multiple "asan_globals" sections, __start_asan_globals is
+// treated as a strong GC reference to the first such section. As a result, the
+// first (for some definition of the word) global is never gc-ed.
+int first_unused = 42;
+
+// On i386 clang adds --export-dynamic when linking with ASan, which adds all
+// non-hidden globals to GC roots.
+__attribute__((visibility("hidden"))) int (*unused)() = undefined;
 
 int main() {
         return 0;
 }