[Patch 5/8, Arm, GCC] Implement target feature macros for PACBTI. [Was RE: [Patch 4/7, Arm. GCC] Implement target feature macros for PACBTI.]

[Richard Earnshaw]

On 28/10/2021 12:43, Tejas Belagod via Gcc-patches wrote:
> 
> 
>> -----Original Message-----
>> From: Richard Earnshaw <Richard.Earnshaw@arm.com>
>> Sent: Monday, October 11, 2021 2:58 PM
>> To: Tejas Belagod <Tejas.Belagod@arm.com>; gcc-patches@gcc.gnu.org
>> Subject: Re: [Patch 4/7, Arm. GCC] Implement target feature macros for
>> PACBTI.
>>
>> On 08/10/2021 13:18, Tejas Belagod via Gcc-patches wrote:
>>> Hi,
>>>
>>> This patch implements target feature macros when PACBTI is enabled
>>> through the -march option or -mbranch-protection.
>>>
>>> Tested on arm-none-eabi. OK for trunk?
>>>
>>> 2021-10-04  Tejas Belagod  <tbelagod@arm.com>
>>>
>>> gcc/ChangeLog:
>>>
>>> 	* config/arm/arm-c.c (arm_cpu_builtins): Define
>>> 	__ARM_FEATURE_BTI_DEFAULT and
>> __ARM_FEATURE_PAC_DEFAULT.
>>>
>>> gcc/testsuite/ChangeLog:
>>>
>>> 	* gcc.target/arm/acle/pacbti-m-predef-2.c: New test.
>>> 	* gcc.target/arm/acle/pacbti-m-predef-4.c: New test.
>>> 	* gcc.target/arm/acle/pacbti-m-predef-5.c: New test.
>>>
>>
>> I presume the specification for this is ACLE - please say so rather than making
>> me guess.
>>
> 
> Yes, sorry, very poor description on my part. Now fixed - please see patch description below for links to specific ACLE sections.
> 
>>
>> +  cpp_undef (pfile, "__ARM_FEATURE_BTI_DEFAULT");
>> +  cpp_undef (pfile, "__ARM_FEATURE_PAC_DEFAULT");
>> +  if (TARGET_HAVE_PACBTI)
>> +    {
>> +      builtin_define_with_int_value ("__ARM_FEATURE_BTI_DEFAULT",
>> +				     arm_enable_pacbti & 0x1);
>>
>> My reading of the ACLE specification would suggest this shouldn't be
>> defined if it would have a value of 0, but that's not what this code
>> does.  I think it would be better to move this outside the
>> TARGET_HAVE_PACBTI and use the def_or_undef approach.
>>
>> +      builtin_define_with_int_value ("__ARM_FEATURE_PAC_DEFAULT",
>> +				     arm_enable_pacbti >> 1);
>>
>> This one is less clear, could the value ever be zero?  I guess exactly
>> one of a-key and b-key must be defined and each has a separate bit.
>>
> 
> Now fixed according to what the arch specifies. For the M-profile, there's only one key which means when -mbranch-protection is invoked, bit 0 is always 1.
> 
>> +    }
>> +
>> +
>>
>> Not more than one blank line at the end of a block.
>>
>>
>> diff --git a/gcc/testsuite/gcc.target/arm/acle/pacbti-m-predef-2.c
>> b/gcc/testsuite/gcc.target/arm/acle/pacbti-m-predef-2.c
>>
>>
>> Given what I've said above, I think you need to also test that
>> __ARM_FEATURE_BTI_DEFAULT is defined before testing the value (and
>> emitting #error if it isn't).
>>
> 
> Fixed.
> 
> This patch implements target feature macros when PACBTI is
> enabled through the -march option or -mbranch-protection.
> The target feature macros __ARM_FEATURE_PAC_DEFAULT and
> __ARM_FEATURE_BTI_DEFAULT are specified in ARM ACLE
> (https://developer.arm.com/documentation/101028/0012/5--Feature-test-macros?lang=en)
> __ARM_FEATURE_PAUTH and __ARM_FEATURE_BTI are specified in the pull-request
> (https://github.com/ARM-software/acle/pull/55).
> 
> 2021-10-25  Tejas Belagod  <tbelagod@arm.com>
> 
> gcc/ChangeLog:
> 
> 	* config/arm/arm-c.c (arm_cpu_builtins): Define
> 	__ARM_FEATURE_BTI_DEFAULT, __ARM_FEATURE_PAC_DEFAULT,
> 	__ARM_FEATURE_PAUTH and __ARM_FEATURE_BTI.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* gcc.target/arm/acle/pacbti-m-predef-2.c: New test.
> 	* gcc.target/arm/acle/pacbti-m-predef-4.c: New test.
> 	* gcc.target/arm/acle/pacbti-m-predef-5.c: New test.
> 
> Tested the following configurations, OK for trunk?
> 
> -mthumb/-march=armv8.1-m.main+pacbti/-mfloat-abi=soft
> -marm/-march=armv7-a/-mfpu=vfpv3-d16/-mfloat-abi=softfp
> mcmodel=small and tiny
> aarch64-none-linux-gnu native test and bootstrap
> 
> Thanks,
> Tejas.
> 


OK.

R.