[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/docs/LangRef.rst b/llvm/docs/LangRef.rst
index 5bbbf32..5a62bff 100644
--- a/llvm/docs/LangRef.rst
+++ b/llvm/docs/LangRef.rst
@@ -1699,6 +1699,12 @@
show that no exceptions passes by it. This is normally the case for
the ELF x86-64 abi, but it can be disabled for some compilation
units.
+``nocf_check``
+ This attribute indicates that no control-flow check will be perfomed on
+ the attributed entity. It disables -fcf-protection=<> for a specific
+ entity to fine grain the HW control flow protection mechanism. The flag
+ is target independant and currently appertains to a function or function
+ pointer.
.. _glattrs: