Re: [PATCH v2 1/2] arm64: Add macro version of the BTI instruction

BTI is only available from v8.5 so we need to encode it using HINT in
generic code and for older toolchains. Add an assembler macro written
by Mark Rutland which lets us use the mnemonic and update the existing
users.

Suggested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
 arch/arm64/crypto/aes-modes.S      | 10 +++++-----
 arch/arm64/include/asm/assembler.h | 18 ++++++++++++++++++
 arch/arm64/include/asm/linkage.h   |  7 +------
 3 files changed, 24 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/crypto/aes-modes.S b/arch/arm64/crypto/aes-modes.S
index b495de22bb38..ff01f0167ba2 100644
--- a/arch/arm64/crypto/aes-modes.S
+++ b/arch/arm64/crypto/aes-modes.S

@@ -363,15 +363,15 @@ ST5(      mov             v4.16b, vctr.16b                )
        adr             x16, 1f
        sub             x16, x16, x12, lsl #3
        br              x16
-       hint            34                      // bti c
+       bti             c
        mov             v0.d[0], vctr.d[0]
-       hint            34                      // bti c
+       bti             c
        mov             v1.d[0], vctr.d[0]
-       hint            34                      // bti c
+       bti             c
        mov             v2.d[0], vctr.d[0]
-       hint            34                      // bti c
+       bti             c
        mov             v3.d[0], vctr.d[0]
-ST5(   hint            34                              )
+ST5(   bti             c                               )
 ST5(   mov             v4.d[0], vctr.d[0]              )
 1:     b               2f
        .previous

diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index 136d13f3d6e9..87f296198366 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h

@@ -790,6 +790,24 @@ alternative_endif
 .Lnoyield_\@:
        .endm

+/*
+ * Branch Target Identifier (BTI)
+ */
+       .macro  bti, targets
+       .equ    .L__bti_targets_c, 1
+       .equ    .L__bti_targets_j, 2
+       .equ    .L__bti_targets_jc,3

+       .if     .L__bti_targets_\targets == .L__bti_targets_c
+       hint    #34
+       .elseif .L__bti_targets_\targets == .L__bti_targets_j
+       hint    #36
+       .elseif .L__bti_targets_\targets == .L__bti_targets_jc
+       hint    #38
+       .else
+       .error  "Unsupported BTI targets '\targets\()'"
+       .endif
+       .endm
+
 /*
  * This macro emits a program property note section identifying
  * architecture features which require special handling, mainly for

diff --git a/arch/arm64/include/asm/linkage.h b/arch/arm64/include/asm/linkage.h
index 9906541a6861..c5d0c11d7709 100644
--- a/arch/arm64/include/asm/linkage.h
+++ b/arch/arm64/include/asm/linkage.h

@@ -6,12 +6,7 @@

 #if defined(CONFIG_ARM64_BTI_KERNEL) && defined(__aarch64__)

-/*
- * Since current versions of gas reject the BTI instruction unless we
- * set the architecture version to v8.5 we use the hint instruction
- * instead.
- */
-#define BTI_C hint 34 ;
+#define BTI_C bti c ;

 /*
  * When using in-kernel BTI we need to ensure that PCS-conformant assembly
--

2.30.2