[compiler-rt] [tsan][NFCI] Add note that GPU libraries may cause shadow mapping incompatibility (PR #137835)

[Thurston Dang via llvm-commits]

================
@@ -292,8 +292,12 @@ static void ReExecIfNeeded(bool ignore_heap) {
     } else {
       Printf(
           "FATAL: ThreadSanitizer: memory layout is incompatible, "
-          "even though ASLR is disabled.\n"
-          "Please file a bug.\n");
+          "even though ASLR is disabled.\n");
+      Printf(
+          "FATAL: This error may occur for programs that use GPU libraries.");
----------------
thurstond wrote:

> Why do we need to mention GPU?
> 
> I can see this can help some users, but it also can misleads other users, who has issue, but no GPU libraries.

It won't mislead them if they have no GPU libraries - the next line is "If your program does not use GPU libraries, please file a TSan bug."

> If we can detect The Library, then maybe there is a value in the message.
> 
> What is % of total issues do we expect caused by GPU libraries? We need a confidence that it's high to blame them.

So far, 100% of issues (sample size = 1) :-).

Most non-GPU libraries aren't mapping large host memory buffers before the shadow is allocated.


https://github.com/llvm/llvm-project/pull/137835