[compiler-rt] [msan] Re-exec with no ASLR if memory layout is incompatible on Linux (PR #85142)

[Thurston Dang via llvm-commits]

================
@@ -138,27 +144,64 @@ bool InitShadow(bool init_origins) {
     bool protect = type == MappingDesc::INVALID ||
                    (!init_origins && type == MappingDesc::ORIGIN);
     CHECK(!(map && protect));
-    if (!map && !protect)
-      CHECK(type == MappingDesc::APP);
+    if (!map && !protect) {
+      CHECK(type == MappingDesc::APP || type == MappingDesc::ALLOCATOR);
+
+      if (type == MappingDesc::ALLOCATOR &&
+          !CheckMemoryRangeAvailability(start, size, !dry_run))
+        return false;
+    }
     if (map) {
-      if (!CheckMemoryRangeAvailability(start, size))
+      if (!CheckMemoryRangeAvailability(start, size, !dry_run))
         return false;
-      if (!MmapFixedSuperNoReserve(start, size, kMemoryLayout[i].name))
+      if (!dry_run &&
+          !MmapFixedSuperNoReserve(start, size, kMemoryLayout[i].name))
         return false;
-      if (common_flags()->use_madv_dontdump)
+      if (!dry_run && common_flags()->use_madv_dontdump)
         DontDumpShadowMemory(start, size);
     }
     if (protect) {
-      if (!CheckMemoryRangeAvailability(start, size))
+      if (!CheckMemoryRangeAvailability(start, size, !dry_run))
         return false;
-      if (!ProtectMemoryRange(start, size, kMemoryLayout[i].name))
+      if (!dry_run && !ProtectMemoryRange(start, size, kMemoryLayout[i].name))
         return false;
     }
   }
 
   return true;
 }
 
+bool InitShadowWithReExec(bool init_origins) {
+  // Start with dry run: check layout is ok, but don't print warnings because
+  // warning messages will cause tests to fail (even if we successfully re-exec
+  // after the warning).
+  bool success = InitShadow(__msan_get_track_origins(), true);
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thurstond wrote:

When InitShadow is called the first time (dry run), it calls CheckMemoryRangeAvailability() but not MmapFixedSuperNoReserve() or ProtectMemoryRange(), so it shouldn't be that expensive.

https://github.com/llvm/llvm-project/pull/85142