ArmPkg: Emit BTI opcodes when BTI codegen is enabled

When building with -mbranch-protection=bti, which affects the compiler
codegen only, ensure that the assembler based codegen is aligned with
this, by emitting the BTI C opcode at the start of each exported
function. While most exported functions are not in fact ever called
indirectly, whether or not this is the case is a property of the caller
so annotating every exported function is a reasonable default.

While at it, fix two occurrences in ArmPkg of exported functions that
did not use the ASM_FUNC() macro.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Leif Lindholm <quic_llindhol@quicinc.com>
Reviewed-by: Oliver Smith-Denny <osd@smith-denny.com>

ArmPkg/Include/AsmMacroIoLibV8.h

@@ -38,7 +38,8 @@
   .global   Name                  ; \
   .section  #Section, "ax"        ; \
   .type     Name, %function       ; \
-  Name:
+  Name:                           ; \
+  AARCH64_BTI(c)
 
 #define ASM_FUNC(Name)  _ASM_FUNC(ASM_PFX(Name), .text. ## Name)
 

ArmPkg/Library/ArmExceptionLib/AArch64/ExceptionSupport.S

@@ -94,7 +94,6 @@
 
 GCC_ASM_EXPORT(ExceptionHandlersEnd)
 GCC_ASM_EXPORT(CommonCExceptionHandler)
-GCC_ASM_EXPORT(RegisterEl0Stack)
 
 .text
 
@@ -387,6 +386,6 @@ ASM_PFX(CommonExceptionEntry):
 
   eret
 
-ASM_PFX(RegisterEl0Stack):
+ASM_FUNC(RegisterEl0Stack)
   msr     sp_el0, x0
   ret

ArmPkg/Library/ArmSvcLib/AArch64/ArmSvc.S

@@ -5,12 +5,12 @@
 //
 //
 
+#include <AsmMacroIoLibV8.h>
+
 .text
 .align 3
 
-GCC_ASM_EXPORT(ArmCallSvc)
-
-ASM_PFX(ArmCallSvc):
+ASM_FUNC(ArmCallSvc)
   // Push frame pointer and return address on the stack
   stp   x29, x30, [sp, #-32]!
   mov   x29, sp