[X86] Added support for nocf_check attribute for indirect Branch Tracking
X86 Supports Indirect Branch Tracking (IBT) as part of Control-Flow Enforcement Technology (CET).
IBT instruments ENDBR instructions used to specify valid targets of indirect call / jmp.
The `nocf_check` attribute has two roles in the context of X86 IBT technology:
1. Appertains to a function - do not add ENDBR instruction at the beginning of the function.
2. Appertains to a function pointer - do not track the target function of this pointer by adding nocf_check prefix to the indirect-call instruction.
This patch implements `nocf_check` context for Indirect Branch Tracking.
It also auto generates `nocf_check` prefixes before indirect branchs to jump tables that are guarded by range checks.
Differential Revision: https://reviews.llvm.org/D41879
llvm-svn: 327767
diff --git a/llvm/lib/Target/X86/X86FastISel.cpp b/llvm/lib/Target/X86/X86FastISel.cpp
index 9430225..3806d2d 100644
--- a/llvm/lib/Target/X86/X86FastISel.cpp
+++ b/llvm/lib/Target/X86/X86FastISel.cpp
@@ -3174,6 +3174,13 @@
CLI.CS ? dyn_cast<CallInst>(CLI.CS->getInstruction()) : nullptr;
const Function *CalledFn = CI ? CI->getCalledFunction() : nullptr;
+ // Call / invoke instructions with NoCfCheck attribute require special
+ // handling.
+ const auto *II =
+ CLI.CS ? dyn_cast<InvokeInst>(CLI.CS->getInstruction()) : nullptr;
+ if ((CI && CI->doesNoCfCheck()) || (II && II->doesNoCfCheck()))
+ return false;
+
// Functions with no_caller_saved_registers that need special handling.
if ((CI && CI->hasFnAttr("no_caller_saved_registers")) ||
(CalledFn && CalledFn->hasFnAttribute("no_caller_saved_registers")))