[compiler-rt] [llvm] [msan] Automatically print shadow for failing outlined checks (PR #145107)

[Vitaly Buka via llvm-commits]

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@@ -352,23 +352,70 @@ void __sanitizer::BufferedStackTrace::UnwindImpl(
 
 using namespace __msan;
 
-#define MSAN_MAYBE_WARNING(type, size)              \
-  void __msan_maybe_warning_##size(type s, u32 o) { \
-    GET_CALLER_PC_BP;                               \
-    if (UNLIKELY(s)) {                              \
-      PrintWarningWithOrigin(pc, bp, o);            \
-      if (__msan::flags()->halt_on_error) {         \
-        Printf("Exiting\n");                        \
-        Die();                                      \
-      }                                             \
-    }                                               \
+// N.B. Only [shadow, shadow+size) is defined. shadow is *not* a pointer into
+// an MSan shadow region.
+static void print_shadow_value(void *shadow, u64 size) {
+  Printf("\n");
+  Printf("Shadow value (%llu byte%s):", size, size == 1 ? "" : "s");
+  for (unsigned int i = 0; i < size; i++) {
+    if (i % 4 == 0)
+      Printf(" ");
+
+    unsigned char x = ((unsigned char *)shadow)[i];
+    Printf("%x%x", x >> 4, x & 0xf);
+  }
+  Printf("\n");
+  Printf(
+      "Caveat: the shadow value does not necessarily directly correspond to a "
+      "single user variable. The correspondence is stronger, but not always "
+      "perfect, when origin tracking is enabled.\n");
+  Printf("\n");
+}
+
+#define MSAN_MAYBE_WARNING(type, size)               \
+  void __msan_maybe_warning_##size(type s, u32 o) {  \
+    GET_CALLER_PC_BP;                                \
+                                                     \
+    if (UNLIKELY(s)) {                               \
+      PrintWarningWithOrigin(pc, bp, o);             \
+      if (Verbosity() >= 1)                          \
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vitalybuka wrote:

should go before warning

https://github.com/llvm/llvm-project/pull/145107