string: Add M-profile PACBTI implementation of memchr

Ensure BTI indirect branch landing pads (BTI) and pointer authentication
code genetaion (PAC) and verification instructions (BXAUT) are
conditionally added to assembly when branch protection is requested

1 files changed, 37 insertions, 3 deletions

diff --git a/string/arm/memchr.S b/string/arm/memchr.S
index 1271ca1..4f7d8f4 100644
--- a/string/arm/memchr.S
+++ b/string/arm/memchr.S
@@ -23,7 +23,11 @@
 @    Removed unneeded cbz from align loop
 
 	.syntax unified
+#if __ARM_ARCH_8M_MAIN__
+    /* keep config inherited from -march= */
+#else
 	.arch armv7-a
+#endif
 
 @ this lets us check a flag in a 00/ff byte easily in either endianness
 #ifdef __ARMEB__
@@ -33,17 +37,22 @@
 #endif
 	.thumb
 
+#include "../pacbti.h"
+
 @ ---------------------------------------------------------------------------
 	.thumb_func
 	.align 2
 	.p2align 4,,15
 	.global __memchr_arm
 	.type __memchr_arm,%function
+	.fnstart
+	.cfi_startproc
 __memchr_arm:
 	@ r0 = start of memory to scan
 	@ r1 = character to look for
 	@ r2 = length
 	@ returns r0 = pointer to character or NULL if not found
+	pacbti_prologue
 	and	r1,r1,#0xff	@ Don't think we can trust the caller to actually pass a char
 
 	cmp	r2,#16		@ If it's short don't bother with anything clever
@@ -64,6 +73,19 @@ __memchr_arm:
 10:
 	@ At this point, we are aligned, we know we have at least 8 bytes to work with
 	push	{r4,r5,r6,r7}
+	.save   {r4-r7}
+	.cfi_adjust_cfa_offset 16
+#ifdef __ARM_FEATURE_PAC_DEFAULT
+	.cfi_offset 4, -8
+	.cfi_offset 5, -12
+	.cfi_offset 6, -16
+	.cfi_offset 7, -20
+#else
+	.cfi_offset 4, -4
+	.cfi_offset 5, -8
+	.cfi_offset 6, -12
+	.cfi_offset 7, -16
+#endif /*  __ARM_FEATURE_PAC_DEFAULT */
 	orr	r1, r1, r1, lsl #8	@ expand the match word across to all bytes
 	orr	r1, r1, r1, lsl #16
 	bic	r4, r2, #7	@ Number of double words to work with
@@ -83,6 +105,11 @@ __memchr_arm:
 	bne	15b		@ (Flags from the subs above) If not run out of bytes then go around again
 
 	pop	{r4,r5,r6,r7}
+	.cfi_restore 7
+	.cfi_restore 6
+	.cfi_restore 5
+	.cfi_restore 4
+	.cfi_adjust_cfa_offset -16
 	and	r1,r1,#0xff	@ Get r1 back to a single character from the expansion above
 	and	r2,r2,#7	@ Leave the count remaining as the number after the double words have been done
  
@@ -98,11 +125,11 @@ __memchr_arm:
 
 40:
 	movs	r0,#0		@ not found
-	bx	lr
+	pacbti_epilogue
 
 50:
 	subs	r0,r0,#1	@ found
-	bx	lr
+	pacbti_epilogue
 
 60:  @ We're here because the fast path found a hit - now we have to track down exactly which word it was
 	@ r0 points to the start of the double word after the one that was tested
@@ -126,7 +153,14 @@ __memchr_arm:
 
 61:
 	pop	{r4,r5,r6,r7}
+	.cfi_restore 7
+	.cfi_restore 6
+	.cfi_restore 5
+	.cfi_restore 4
+	.cfi_adjust_cfa_offset -16
 	subs	r0,r0,#1
-	bx	lr
+	pacbti_epilogue
+	.cfi_endproc
+	.fnend
 
 	.size	__memchr_arm, . - __memchr_arm