[hwasan] Allow optional early shadow setup.

Summary:
Provide __hwasan_shadow_init that can be used to initialize shadow w/o touching libc.
It can be used to bootstrap an unusual case of fully-static executable with
hwasan-instrumented libc, which needs to run hwasan code before it is ready to serve
user calls like madvise().

Reviewers: vitalybuka, kcc

Subscribers: kubamracek, llvm-commits

Differential Revision: https://reviews.llvm.org/D50581

1 files changed, 6 insertions, 0 deletions

diff --git a/compiler-rt/include/sanitizer/hwasan_interface.h b/compiler-rt/include/sanitizer/hwasan_interface.h
index 0c306cf279e..7f0d36f718b 100644
--- a/compiler-rt/include/sanitizer/hwasan_interface.h
+++ b/compiler-rt/include/sanitizer/hwasan_interface.h
@@ -19,6 +19,12 @@
 #ifdef __cplusplus
 extern "C" {
 #endif
+  // Initialize shadow but not the rest of the runtime.
+  // Does not call libc unless there is an error.
+  // Can be called multiple times, or not at all (in which case shadow will
+  // be initialized in compiler-inserted __hwasan_init() call).
+  void __hwasan_shadow_init(void);
+
   // This function may be optionally provided by user and should return
   // a string containing HWASan runtime options. See asan_flags.h for details.
   const char* __hwasan_default_options(void);