[PATCH v5b 8/8] newlib: libc: setjmp M-profile PACBTI-enablement

This patch revision provides the following improvements to proposed
patch implementation:
  * Load ip directly when restoring PAC code from stack for
  authentication in longjmp epilogue.
  * Improve code readability by defining the JUMPBUF_PAC macro to
  map onto the otherwise obscure 104 constant used in str/ldr
  instructions.

Add function prologue/epilogue to conditionally add BTI landing pads
and/or PAC code generation & authentication instructions depending on
compilation flags.
---
 newlib/libc/machine/arm/setjmp.S | 43 ++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/newlib/libc/machine/arm/setjmp.S b/newlib/libc/machine/arm/setjmp.S
index d814afea8..5213c063b 100644
--- a/newlib/libc/machine/arm/setjmp.S
+++ b/newlib/libc/machine/arm/setjmp.S
@@ -22,6 +22,11 @@
 #define SIZE(x)
 #endif
 
+/* Jump buffer allocation sizes.  */
+#define JUMPBUF_CORE_REGS_SIZE (10 * 4)
+#define JUMPBUF_FP_REGS_SIZE (8 * 8)
+#define JUMPBUF_PAC (JUMPBUF_CORE_REGS_SIZE + JUMPBUF_FP_REGS_SIZE + 0)
+
 /* Arm/Thumb interworking support:
 
    The interworking scheme expects functions to use a BX instruction
@@ -155,6 +160,8 @@ SYM (.arm_start_of.\name):
 	.align 2
 	MODE
 	.globl SYM (\name)
+	.fnstart
+	.cfi_startproc
 	TYPE (\name)
 SYM (\name):
 	PROLOGUE \name
@@ -162,6 +169,8 @@ SYM (\name):
 
 .macro FUNC_END name
 	RET
+	.cfi_endproc
+	.fnend
 	SIZE (\name)
 .endm
 
@@ -171,6 +180,21 @@ SYM (\name):
 
 	FUNC_START setjmp
 
+#if __ARM_FEATURE_PAC_DEFAULT
+# if __ARM_FEATURE_BTI_DEFAULT
+	pacbti	ip, lr, sp
+# else
+	pac	ip, lr, sp
+# endif /* __ARM_FEATURE_BTI_DEFAULT */
+	mov r3, ip
+	str r3, [r0, #JUMPBUF_PAC]
+	.cfi_register 143, 12
+#else
+# if __ARM_FEATURE_BTI_DEFAULT
+	bti
+# endif /* __ARM_FEATURE_BTI_DEFAULT */
+#endif /* __ARM_FEATURE_PAC_DEFAULT */
+
 	/* Save all the callee-preserved registers into the jump buffer.  */
 #ifdef __thumb2__
 	mov		ip, sp
@@ -184,6 +208,10 @@ SYM (\name):
 
 	/* When setting up the jump buffer return 0.  */
 	mov		r0, #0
+#if __ARM_FEATURE_PAC_DEFAULT
+	mov ip, r3
+	aut ip, lr, sp
+#endif /* __ARM_FEATURE_PAC_DEFAULT */
 
 	FUNC_END setjmp
 
@@ -193,6 +221,16 @@ SYM (\name):
 
 	FUNC_START longjmp
 
+#if __ARM_FEATURE_BTI_DEFAULT
+	bti
+#endif /* __ARM_FEATURE_BTI_DEFAULT */
+
+#if __ARM_FEATURE_PAC_DEFAULT
+	/* Keep original jmpbuf address for retrieving pac-code
+	   for authentication.  */
+	mov	r2, r0
+#endif /* __ARM_FEATURE_PAC_DEFAULT */
+
 	/* If we have stack extension code it ought to be handled here.  */
 
 	/* Restore the registers, retrieving the state when setjmp() was called.  */
@@ -212,5 +250,10 @@ SYM (\name):
 	it		eq
 	moveq		r0, #1
 
+#if __ARM_FEATURE_PAC_DEFAULT
+	ldr ip, [r2, #JUMPBUF_PAC]
+	aut ip, lr, sp
+#endif /* __ARM_FEATURE_PAC_DEFAULT */
+
 	FUNC_END longjmp
 #endif
-- 
2.36.1