[ASan] Use __sanitizer_fill_shadow for FastPoisonShadow on Fuchsia

[phosek]

Summary

This is the optimized implementation for Fuchsia provided by the libc.

[phosek]

Alternatively, I can move FastPoisonShadow implementation to asan_poisoning.cc and asan_fuchsia.cc and implement them separately for each platform, but we would loose the inlining if we do that.

[mcgrathr]

AFAICT the inlining is the whole point of FastPoisonShadow so this LGTM as is.

compiler-rt/lib/asan/asan_poisoning.h

76

// SANITIZER_FUCHSIA?

[eugenis]

LGTM

compiler-rt/lib/asan/asan_poisoning.h

 //
 // Shadow memory poisoning by ASan RTL and by user application.
 //===----------------------------------------------------------------------===//
 
 #include "asan_interceptors.h"
 #include "asan_internal.h"
 #include "asan_mapping.h"
 #include "sanitizer_common/sanitizer_flags.h"
+#include "sanitizer_common/sanitizer_platform.h"
 
 namespace __asan {
 
 // Enable/disable memory poisoning.
 void SetCanPoisonMemory(bool value);
 bool CanPoisonMemory();
 
 // Poisons the shadow memory for "size" bytes starting from "addr".
 void PoisonShadow(uptr addr, uptr size, u8 value);
 
 // Poisons the shadow memory for "redzone_size" bytes starting from
 // "addr + size".
 void PoisonShadowPartialRightRedzone(uptr addr,
                                      uptr size,
                                      uptr redzone_size,
                                      u8 value);
 
 // Fast versions of PoisonShadow and PoisonShadowPartialRightRedzone that
 // assume that memory addresses are properly aligned. Use in
 // performance-critical code with care.
 ALWAYS_INLINE void FastPoisonShadow(uptr aligned_beg, uptr aligned_size,
                                     u8 value) {
   DCHECK(!value || CanPoisonMemory());
+#if SANITIZER_FUCHSIA
+  __sanitizer_fill_shadow(aligned_beg, aligned_size, value,
+                          common_flags()->clear_shadow_mmap_threshold);
+#else
   uptr shadow_beg = MEM_TO_SHADOW(aligned_beg);
   uptr shadow_end = MEM_TO_SHADOW(
       aligned_beg + aligned_size - SHADOW_GRANULARITY) + 1;
   // FIXME: Page states are different on Windows, so using the same interface
   // for mapping shadow and zeroing out pages doesn't "just work", so we should
   // probably provide higher-level interface for these operations.
   // For now, just memset on Windows.
   if (value || SANITIZER_WINDOWS == 1 ||
-      // TODO(mcgrathr): Fuchsia doesn't allow the shadow mapping to be
-      // changed at all.  It doesn't currently have an efficient means
-      // to zero a bunch of pages, but maybe we should add one.
-      SANITIZER_FUCHSIA == 1 ||
       // RTEMS doesn't have have pages, let alone a fast way to zero
       // them, so default to memset.
       SANITIZER_RTEMS == 1 ||
       shadow_end - shadow_beg < common_flags()->clear_shadow_mmap_threshold) {
     REAL(memset)((void*)shadow_beg, value, shadow_end - shadow_beg);
   } else {
     uptr page_size = GetPageSizeCached();
     uptr page_beg = RoundUpTo(shadow_beg, page_size);
     uptr page_end = RoundDownTo(shadow_end, page_size);
 
     if (page_beg >= page_end) {
       REAL(memset)((void *)shadow_beg, 0, shadow_end - shadow_beg);
     } else {
       if (page_beg != shadow_beg) {
         REAL(memset)((void *)shadow_beg, 0, page_beg - shadow_beg);
       }
       if (page_end != shadow_end) {
         REAL(memset)((void *)page_end, 0, shadow_end - page_end);
       }
       ReserveShadowMemoryRange(page_beg, page_end - 1, nullptr);
     }
   }
+#endif // SANITIZER_FUCHSIA
 }
 
 ALWAYS_INLINE void FastPoisonShadowPartialRightRedzone(
     uptr aligned_addr, uptr size, uptr redzone_size, u8 value) {
   DCHECK(CanPoisonMemory());
   bool poison_partial = flags()->poison_partial;
   u8 *shadow = (u8*)MEM_TO_SHADOW(aligned_addr);
   for (uptr i = 0; i < redzone_size; i += SHADOW_GRANULARITY, shadow++) {