[compiler-rt] Reland '[hwasan] Add fixed_shadow_base flag (#73980)' (PR #95445)

[Florian Mayer via llvm-commits]

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@@ -106,8 +106,12 @@ static uptr GetHighMemEnd() {
 }
 
 static void InitializeShadowBaseAddress(uptr shadow_size_bytes) {
-  __hwasan_shadow_memory_dynamic_address =
-      FindDynamicShadowStart(shadow_size_bytes);
+  if (!SANITIZER_ANDROID && flags()->fixed_shadow_base != (uptr)-1) {
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fmayer wrote:

Please add a comment why we are doing this here.

https://github.com/llvm/llvm-project/pull/95445