[hwasan] Improve report for addresses within regions.

[fmayer]

Summary

Before: ADDR is located -320 bytes to the right of 1072-byte region
After: ADDR is located 752 bytes inside 1072-byte region

[eugenis]

LGTM

compiler-rt/lib/hwasan/hwasan_report.cpp

for (int i = 0; i < 1000; i++) {
     }
     ++right;
   }
 
   if (candidate) {
     uptr mem = ShadowToMem(reinterpret_cast<uptr>(candidate));
     HwasanChunkView chunk = FindHeapChunkByAddress(mem);
     if (chunk.IsAllocated()) {
+      uptr offset;
+      const char *whence;
+      if (untagged_addr < chunk.End() && untagged_addr >= chunk.Beg()) {
+        offset = untagged_addr - chunk.Beg();
+        whence = "inside";
+      } else if (candidate == left) {
+        offset = untagged_addr - chunk.End();
+        whence = "to the right of";
+      } else {
+        offset = chunk.Beg() - untagged_addr;
+        whence = "to the left of";
+      }
       Printf("%s", d.Location());
-      Printf("%p is located %zd bytes to the %s of %zd-byte region [%p,%p)\n",
-             untagged_addr,
-             candidate == left ? untagged_addr - chunk.End()
-                               : chunk.Beg() - untagged_addr,
-             candidate == left ? "right" : "left", chunk.UsedSize(),
-             chunk.Beg(), chunk.End());
+      Printf("%p is located %zd bytes %s %zd-byte region [%p,%p)\n",
+             untagged_addr, offset, whence, chunk.UsedSize(), chunk.Beg(),
+             chunk.End());
       Printf("%s", d.Allocation());
       Printf("allocated here:\n");
       Printf("%s", d.Default());
       GetStackTraceFromId(chunk.GetAllocStackId()).Print();
       num_descriptions_printed++;
     } else {
       // Check whether the address points into a loaded library. If so, this is
       // most likely a global variable.

compiler-rt/test/hwasan/TestCases/heap-buffer-overflow-into.c

+// RUN: %clang_hwasan  %s -o %t
+// RUN: not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK
+
+// REQUIRES: stable-runtime
+
+#include <sanitizer/hwasan_interface.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+int main(int argc, char **argv) {
+  __hwasan_enable_allocator_tagging();
+  char *volatile x = (char *)malloc(10);
+  memset(x + 5, 0, 26);
+  // CHECK: is located 5 bytes inside 10-byte region
+  free(x);
+}