[PATCH v2 3/8] newlib: libc: strlen M-profile PACBTI-enablement

[Victor Do Nascimento]

Add function prologue/epilogue to conditionally add BTI landing pads
and/or PAC code generation & authentication instructions depending on
compilation flags.

This patch enables PACBTI for all relevant variants of strlen:
     * Newlib for armv8.1-m.main+pacbti
     * Newlib for armv8.1-m.main+pacbti+mve
     * Newlib-nano
---
 newlib/libc/machine/arm/strlen-armv7.S     | 53 ++++++++++++++++++++--
 newlib/libc/machine/arm/strlen-thumb2-Os.S | 13 ++++--
 2 files changed, 60 insertions(+), 6 deletions(-)

diff --git a/newlib/libc/machine/arm/strlen-armv7.S b/newlib/libc/machine/arm/strlen-armv7.S
index f3dda0d60..0492800f9 100644
--- a/newlib/libc/machine/arm/strlen-armv7.S
+++ b/newlib/libc/machine/arm/strlen-armv7.S
@@ -59,6 +59,7 @@
    OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.  */
 
 #include "acle-compat.h"
+#include "pacbti.h"
 
 	.macro def_fn f p2align=0
 	.text
@@ -78,7 +79,11 @@
 
 	/* This code requires Thumb.  */
 #if __ARM_ARCH_PROFILE == 'M'
+#if __ARM_ARCH >= 8
+	/* keep config inherited from -march=.  */
+#else
 	.arch   armv7e-m
+#endif /* if __ARM_ARCH >= 8 */
 #else
 	.arch	armv6t2
 #endif
@@ -100,8 +105,35 @@
 #define tmp2		r5
 
 def_fn	strlen p2align=6
+	.fnstart
+	.cfi_startproc
+	/* common pacbti_prologue macro from pacbti.h not used.
+	   handwritten prologue saves one push instruction.  */
+#if __HAVE_PAC_LEAF
+#if __ARM_FEATURE_BTI_DEFAULT
+	pacbti ip, lr, sp
+#else
+	pac ip, lr, sp
+#endif /* __ARM_FEATURE_BTI_DEFAULT */
+	.cfi_register 143, 12
+	push    {r4, r5, ip}
+	.save   {r4, r5, ra_auth_code}
+	.cfi_def_cfa_offset 12
+	.cfi_offset 143, -4
+	.cfi_offset 5, -8
+	.cfi_offset 4, -12
+
+#else
+#if __ARM_FEATURE_BTI_DEFAULT
+	bti
+#endif /* __ARM_FEATURE_BTI_DEFAULT */
+	push    {r4, r5}
+	.save   {r4, r5}
+	.cfi_def_cfa_offset 8
+	.cfi_offset 5, -4
+	.cfi_offset 4, -8
+#endif /* __HAVE_PAC_LEAF */
 	pld	[srcin, #0]
-	strd	r4, r5, [sp, #-8]!
 	bic	src, srcin, #7
 	mvn	const_m1, #0
 	ands	tmp1, srcin, #7		/* (8 - bytes) to alignment.  */
@@ -159,9 +191,22 @@ def_fn	strlen p2align=6
 	rev	data1a, data1a
 #endif
 	clz	data1a, data1a
-	ldrd	r4, r5, [sp], #8
 	add	result, result, data1a, lsr #3	/* Bits -> Bytes.  */
-	bx	lr
+#if __HAVE_PAC_LEAF
+	pop	{r4, r5, ip}
+	.cfi_restore 4
+	.cfi_restore 5
+	.cfi_restore 143
+	.cfi_def_cfa_offset 0
+	aut ip, lr, sp
+#else
+	ldrd	r4, r5, [sp], #8
+	.cfi_restore 4
+	.cfi_restore 5
+	.cfi_def_cfa_offset 0
+#endif /* __HAVE_PAC_LEAF */
+	bx lr
+
 
 .Lmisaligned8:
 	ldrd	data1a, data1b, [src]
@@ -177,4 +222,6 @@ def_fn	strlen p2align=6
 	movne	data1a, const_m1
 	mov	const_0, #0
 	b	.Lstart_realigned
+	.cfi_endproc
+	.fnend
 	.size	strlen, . - strlen
diff --git a/newlib/libc/machine/arm/strlen-thumb2-Os.S b/newlib/libc/machine/arm/strlen-thumb2-Os.S
index 961f41a0a..571068dac 100644
--- a/newlib/libc/machine/arm/strlen-thumb2-Os.S
+++ b/newlib/libc/machine/arm/strlen-thumb2-Os.S
@@ -25,6 +25,7 @@
    OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.  */
 
 #include "acle-compat.h"
+#include "pacbti.h"
 
 	.macro def_fn f p2align=0
 	.text
@@ -33,8 +34,9 @@
 	.type \f, %function
 \f:
 	.endm
-
-#if __ARM_ARCH_ISA_THUMB >= 2 && __ARM_ARCH >= 7
+#if __ARM_ARCH_PROFILE == 'M' && __ARM_ARCH >= 8
+	/* keep config inherited from -march=.  */
+#elif __ARM_ARCH_ISA_THUMB >= 2 && __ARM_ARCH >= 7
 	.arch   armv7
 #else
 	.arch	armv6t2
@@ -44,11 +46,16 @@
 	.syntax unified
 
 def_fn	strlen p2align=1
+	.fnstart
+	.cfi_startproc
+	pacbti_prologue
 	mov     r3, r0
 1:	ldrb.w  r2, [r3], #1
 	cmp     r2, #0
 	bne	1b
 	subs    r0, r3, r0
 	subs    r0, #1
-	bx      lr
+	pacbti_epilogue
+	.cfi_endproc
+	.fnend
 	.size	strlen, . - strlen
-- 
2.36.1