[compiler-rt] [compiler-rt][ctx_profile] Add the instrumented contextual profiling APIs (PR #89838)

[Snehasish Kumar via llvm-commits]

================
@@ -13,11 +13,104 @@
 #include "sanitizer_common/sanitizer_mutex.h"
 #include "sanitizer_common/sanitizer_placement_new.h"
 #include "sanitizer_common/sanitizer_thread_safety.h"
+#include "sanitizer_common/sanitizer_vector.h"
 
 #include <assert.h>
 
 using namespace __ctx_profile;
 
+namespace {
+// Keep track of all the context roots we actually saw, so we can then traverse
+// them when the user asks for the profile in __llvm_ctx_profile_fetch
+__sanitizer::SpinMutex AllContextsMutex;
+SANITIZER_GUARDED_BY(AllContextsMutex)
+__sanitizer::Vector<ContextRoot *> AllContextRoots;
+
+// utility to taint a pointer by setting the LSB. There is an assumption
+// throughout that the addresses of contexts are even (really, they should be
+// align(8), but "even"-ness is the minimum assumption)
----------------
snehasish wrote:

I think the `align(8)` nature is load bearing, see my other comment about reinterpreting the address immediately following the counters array.

https://github.com/llvm/llvm-project/pull/89838