[PATCH 3/8] newlib: libc: strlen M-profile PACBTI-enablement
Richard Earnshaw
Richard.Earnshaw@foss.arm.com
Wed Jul 6 09:07:45 GMT 2022
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
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