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

[Richard Earnshaw <Richard.Earnshaw@foss.arm.com>]

On 05/07/2022 17:30, Victor L. Do Nascimento wrote:
> Richard Earnshaw <Richard.Earnshaw@foss.arm.com> writes:
> 
>> On 05/07/2022 14:58, Victor Do Nascimento wrote:
>>> 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     | 52 ++++++++++++++++++++--
>>>    newlib/libc/machine/arm/strlen-stub.c      |  9 ++++
>>>    newlib/libc/machine/arm/strlen-thumb2-Os.S | 13 ++++--
>>>    3 files changed, 67 insertions(+), 7 deletions(-)
>>> diff --git a/newlib/libc/machine/arm/strlen-armv7.S
>>> b/newlib/libc/machine/arm/strlen-armv7.S
>>> index f3dda0d60..18c8226d0 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
>>> @@ -77,7 +78,9 @@
>>>    #endif
>>>      	/* This code requires Thumb.  */
>>> -#if __ARM_ARCH_PROFILE == 'M'
>>> +#if __ARM_ARCH_8M_MAIN__
>>
>> These GCC architecture macros (those that end with '__') aren't portable and are
>> essentially deprecated.  What exactly are you trying to achieve here?
> 
> It was my attempt at circumventing the .arch directives below.
> As these older architecture lack the support for PACBTI instructions, if
> we don't prevent the selection of the wrong target architecture, when
> said instructions are encountered they cause Newlib compilation to fail.
> 
> In particular, I needed to distinguish between armv7e-m and
> armv8.1-m.main and chose the __ARM_ARCH_8M_MAIN__ macro out of the
> output from using the -dM GCC preprocessor flag.
> 
> Will fix.

I'd suggest you use __ARM_ARCH >= 8, which should be enough 
(technically, of course, it should be >= 800, but GCC is broken on this).

R.

> 
>>> +    /* keep config inherited from -march= */
>>> +#elif __ARM_ARCH_PROFILE == 'M'
>>>    	.arch   armv7e-m
>>>    #else
>>>    	.arch	armv6t2
>>> @@ -100,8 +103,34 @@
>>>    #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 __ARM_FEATURE_PAC_DEFAULT
>>> +#if __ARM_FEATURE_BTI_DEFAULT
>>> +	pacbti ip, lr, sp
>>> +#else
>>> +	pac ip, lr, sp
>>> +#endif /* __ARM_FEATURE_BTI_DEFAULT */
>>> +	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 /* __ARM_FEATURE_PAC_DEFAULT */
>>>    	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 +188,22 @@ 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 __ARM_FEATURE_PAC_DEFAULT
>>> +	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 /* __ARM_FEATURE_PAC_DEFAULT */
>>> +	bx lr
>>> +
>>>      .Lmisaligned8:
>>>    	ldrd	data1a, data1b, [src]
>>> @@ -177,4 +219,6 @@ 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-stub.c b/newlib/libc/machine/arm/strlen-stub.c
>>> index fc2daf16f..4a0bb8cbb 100644
>>> --- a/newlib/libc/machine/arm/strlen-stub.c
>>> +++ b/newlib/libc/machine/arm/strlen-stub.c
>>> @@ -58,6 +58,11 @@ strlen (const char* str)
>>>           "data .req r3\n\t"
>>>           "addr .req r1\n\t"
>>>    +#ifdef __ARM_FEATURE_PAC_DEFAULT
>>> +       "pac ip, lr, sp\n\t"
>>> +       "str ip, [sp, #-4]!\n\t"
>>> +#endif
>>> +
>>>    #ifdef _ISA_ARM_7
>>>           "pld [r0]\n\t"
>>>    #endif
>>> @@ -167,6 +172,10 @@ strlen (const char* str)
>>>           "it	ne\n\t"
>>>           "addne	len, len, #1\n\t"
>>>    # endif
>>> +#endif
>>> +#ifdef __ARM_FEATURE_PAC_DEFAULT
>>> +       "ldr ip, [sp], #4\n\t"
>>> +       "aut ip, lr, sp\n\t"
>>>    #endif
>>>           "bx	lr\n\t");
>>>    }
>>> diff --git a/newlib/libc/machine/arm/strlen-thumb2-Os.S b/newlib/libc/machine/arm/strlen-thumb2-Os.S
>>> index 961f41a0a..823b0310e 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_8M_MAIN__
>>> +	/* 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