[SanCov] Fix sancov global symbol collision due to cap_merged_table in CHERI

When multiple private sancov global variables across object files share the same name,
even though they won't collide when they are linked together, their corresponding
__cap_merged_table will. This commit appends a unique module identifier to the sancov
global variable names to prevent collision. In the event that the unique module identifier
obtained through getUniqueModuleId() is empty, we use the clang PID and time.

Author: RoundofThree

llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp

@@ -15,6 +15,7 @@
 #include "llvm/Transforms/Instrumentation/SanitizerCoverage.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringExtras.h"
 #include "llvm/Analysis/GlobalsModRef.h"
 #include "llvm/Analysis/PostDominators.h"
 #include "llvm/IR/Constant.h"
@@ -30,6 +31,7 @@
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Type.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Process.h"
 #include "llvm/Support/SpecialCaseList.h"
 #include "llvm/Support/VirtualFileSystem.h"
 #include "llvm/TargetParser/Triple.h"
@@ -390,6 +392,10 @@ bool ModuleSanitizerCoverage::instrumentModule(
   DL = &M.getDataLayout();
   CurModule = &M;
   CurModuleUniqueId = getUniqueModuleId(CurModule);
+  if (CurModuleUniqueId.empty()) {
+    CurModuleUniqueId = "clangPidTime_" + llvm::itostr(sys::Process::getProcessId()) +
+      "_" + llvm::itostr(time(nullptr));
+  }
   TargetTriple = Triple(M.getTargetTriple());
   FunctionGuardArray = nullptr;
   Function8bitCounterArray = nullptr;
@@ -724,7 +730,7 @@ GlobalVariable *ModuleSanitizerCoverage::CreateFunctionLocalArrayInSection(
   ArrayType *ArrayTy = ArrayType::get(Ty, NumElements);
   auto Array = new GlobalVariable(
       *CurModule, ArrayTy, false, GlobalVariable::PrivateLinkage,
-      Constant::getNullValue(ArrayTy), "__sancov_gen_");
+      Constant::getNullValue(ArrayTy), Twine("__sancov_gen_") + Twine(CurModuleUniqueId));
 
   if (TargetTriple.supportsCOMDAT() &&
       (TargetTriple.isOSBinFormatELF() || !F.isInterposable()))
@@ -862,7 +868,7 @@ void ModuleSanitizerCoverage::InjectTraceForSwitch(
       GlobalVariable *GV = new GlobalVariable(
           *CurModule, ArrayOfInt64Ty, false, GlobalVariable::InternalLinkage,
           ConstantArray::get(ArrayOfInt64Ty, Initializers),
-          "__sancov_gen_cov_switch_values");
+          Twine("__sancov_gen_cov_switch_values_") + Twine(CurModuleUniqueId));
       IRB.CreateCall(SanCovTraceSwitchFunction,
                      {Cond, IRB.CreatePointerCast(GV, GlobalsInt64PtrTy)});
     }