[Dwarf/AArch64] Return address signing B key dwarf support

- When signing return addresses with -msign-return-address=<scope>{+<key>},
  either the A key instructions or the B key instructions can be used. To
  correctly authenticate the return address, the unwinder/debugger must know
  which key was used to sign the return address.
- When and exception is thrown or a break point reached, it may be necessary to
  unwind the stack. To accomplish this, the unwinder/debugger must be able to
  first authenticate an the return address if it has been signed.
- To enable this, the augmentation string of CIEs has been extended to allow
  inclusion of a 'B' character. Functions that are signed using the B key
  variant of the instructions should have and FDE whose associated CIE has a 'B'
  in the augmentation string.
- One must also be able to preserve these semantics when first stepping from a
  high level language into assembly and then, as a second step, into an object
  file. To achieve this, I have introduced a new assembly directive
  '.cfi_b_key_frame ', that tells the assembler the current frame uses return
  address signing with the B key.
- This ensures that the FDE is associated with a CIE that has 'B' in the
  augmentation string.

Differential Revision: https://reviews.llvm.org/D51798

llvm-svn: 349895

1 files changed, 2 insertions, 0 deletions

diff --git a/llvm/lib/MC/MCParser/AsmParser.cpp b/llvm/lib/MC/MCParser/AsmParser.cpp
index aa07eee4491..5c76c900c74 100644
--- a/llvm/lib/MC/MCParser/AsmParser.cpp
+++ b/llvm/lib/MC/MCParser/AsmParser.cpp
@@ -495,6 +495,7 @@ private:
     DK_CFI_UNDEFINED,
     DK_CFI_REGISTER,
     DK_CFI_WINDOW_SAVE,
+    DK_CFI_B_KEY_FRAME,
     DK_MACROS_ON,
     DK_MACROS_OFF,
     DK_ALTMACRO,
@@ -5293,6 +5294,7 @@ void AsmParser::initializeDirectiveKindMap() {
   DirectiveKindMap[".cfi_undefined"] = DK_CFI_UNDEFINED;
   DirectiveKindMap[".cfi_register"] = DK_CFI_REGISTER;
   DirectiveKindMap[".cfi_window_save"] = DK_CFI_WINDOW_SAVE;
+  DirectiveKindMap[".cfi_b_key_frame"] = DK_CFI_B_KEY_FRAME;
   DirectiveKindMap[".macros_on"] = DK_MACROS_ON;
   DirectiveKindMap[".macros_off"] = DK_MACROS_OFF;
   DirectiveKindMap[".macro"] = DK_MACRO;