Re: [linux-next:master 8264/14724] drivers/firmware/smccc/smccc.c:141:1: error: r7 cannot be used in asm here

[Aneesh Kumar K.V <aneesh.kumar@kernel.org>]

Adding Marc Zyngier and Mark Rutland to the reply. 

Aneesh Kumar K.V <aneesh.kumar@kernel.org> writes:

> Aneesh Kumar K.V <aneesh.kumar@kernel.org> writes:
>
>> kernel test robot <lkp@intel.com> writes:
>>
>>> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
>>> head:   eea3fef32a9cf36abcb5975a5a594e4135a6b026
>>> commit: d8263a131bb05398faa72ac32be54a03e48fa197 [8264/14724] firmware: hwrng: arm_smccc_trng: Register as an SMCCC device
>>> config: arm-randconfig-1001-20261007 (https://download.01.org/0day-ci/archive/20261007/202610070641.B8hxBJcf-lkp@intel.com/config)
>>> compiler: arm-linux-gnueabi-gcc (GCC) 8.5.0
>>> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20261007/202610070641.B8hxBJcf-lkp@intel.com/reproduce)
>>>
>>> If you fix the issue in a separate patch/commit (i.e. not just a new version of
>>> the same patch/commit), kindly add following tags
>>> | Reported-by: kernel test robot <lkp@intel.com>
>>> | Closes: https://lore.kernel.org/oe-kbuild-all/202610070641.B8hxBJcf-lkp@intel.com/
>>>
>>> All errors (new ones prefixed by >>):
>>>
>>>    drivers/firmware/smccc/smccc.c: In function 'smccc_devices_init':
>>>>> drivers/firmware/smccc/smccc.c:141:1: error: r7 cannot be used in asm here
>>>     }
>>>     ^
>>>>> drivers/firmware/smccc/smccc.c:141:1: error: r7 cannot be used in asm here
>>>
>>>
>>> vim +141 drivers/firmware/smccc/smccc.c
>>>
>>> d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  122) 
>>> b83c2d92be719bf Andre Przywara         2021-07-31  123  static int __init smccc_devices_init(void)
>>> b83c2d92be719bf Andre Przywara         2021-07-31  124  {
>>> d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  125) 	struct arm_smccc_device *sdev;
>>> d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  126) 	const struct smccc_device_info *smccc_dev;
>>> d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  127) 
>>> d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  128) 	for (int i = 0; i < ARRAY_SIZE(smccc_devices); i++) {
>>> d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  129) 		smccc_dev = &smccc_devices[i];
>>> d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  130) 
>>> d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  131) 		if (!smccc_probe_smccc_device(smccc_dev))
>>> d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  132) 			continue;
>>> d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  133) 
>>> d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  134) 		sdev = arm_smccc_device_register(smccc_dev->device_name, smccc_dev->func_id);
>>> d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  135) 		if (IS_ERR(sdev))
>>> d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  136) 			pr_err("%s: could not register device: %pe\n",
>>> d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  137) 			       smccc_dev->device_name, sdev);
>>> b83c2d92be719bf Andre Przywara         2021-07-31  138  	}
>>> b83c2d92be719bf Andre Przywara         2021-07-31  139  
>>> b83c2d92be719bf Andre Przywara         2021-07-31  140  	return 0;
>>> b83c2d92be719bf Andre Przywara         2021-07-31 @141  }
>>>
>>
>>
>> This is with:
>>
>> CONFIG_ARM_THUMB=y
>> CONFIG_ARM_THUMBEE=y
>>
>> where there are restrictions on the use of r7. IMHO, this needs to be
>> addressed in the implementation of arm_smccc_1_1_invoke(), rather than
>> worked around in this patch?
>>
>
> Something like this? The -fno-omit-frame-pointer compiler option is
> required to reproduce the build error.
>
> firmware: smccc: Avoid inline r7 constraints for Thumb-2 calls
>
> The SMCCC device probe passes eight register arguments to
> arm_smccc_1_1_invoke(). With GCC 8.5 and CONFIG_THUMB2_KERNEL=y, the
> kernel test robot reports "r7 cannot be used in asm here" while
> compiling smccc_devices_init(). The eight-input inline helpers bind
> the final argument to r7, which GCC cannot allocate in this function.
>
> Use the existing out-of-line SMC and HVC helpers for eight-input calls
> on ARM32 Thumb-2. The helpers load the stack arguments into r4-r7
> before entering firmware and save and restore the caller's registers.
> Preserve all input arguments and provide a temporary result buffer
> when the caller supplies NULL.
>
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202610070641.B8hxBJcf-lkp@intel.com/
> Assisted-by: LLM
> Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
>
> 1 file changed, 70 insertions(+), 3 deletions(-)
> include/linux/arm-smccc.h | 73 +++++++++++++++++++++++++++++++++++++++++++++--
>
> modified   include/linux/arm-smccc.h
> @@ -640,6 +640,39 @@ asmlinkage void __arm_smccc_hvc(unsigned long a0, unsigned long a1,
>  			*___res = (typeof(*___res)){r0, r1, r2, r3};	\
>  	} while (0)
>  
> +#if defined(CONFIG_ARM) && defined(CONFIG_THUMB2_KERNEL)
> +/*
> + * GCC may reserve r7 in Thumb-2 functions. Calls with eight inputs must
> + * therefore use the assembly helpers, which save and restore r7 themselves.
> + */
> +#define __arm_smccc_1_1_out_of_line(fn, inst, a0, a1, a2, a3, a4, a5, a6, a7, res) \
> +	do {\
> +		struct arm_smccc_res __res;\
> +		struct arm_smccc_res *__res_ptr = (res);\
> +\
> +		fn((u32)(a0), a1, a2, a3, a4, a5, a6, a7,\
> +		   __res_ptr ? __res_ptr : &__res);\
> +	} while (0)
> +
> +#define __arm_smccc_1_1_inline(fn, inst, ...) \
> +	__arm_smccc_1_1(inst, __VA_ARGS__)
> +
> +#define __arm_smccc_1_1_call_2 __arm_smccc_1_1_inline
> +#define __arm_smccc_1_1_call_3 __arm_smccc_1_1_inline
> +#define __arm_smccc_1_1_call_4 __arm_smccc_1_1_inline
> +#define __arm_smccc_1_1_call_5 __arm_smccc_1_1_inline
> +#define __arm_smccc_1_1_call_6 __arm_smccc_1_1_inline
> +#define __arm_smccc_1_1_call_7 __arm_smccc_1_1_inline
> +#define __arm_smccc_1_1_call_8 __arm_smccc_1_1_inline
> +#define __arm_smccc_1_1_call_9 __arm_smccc_1_1_out_of_line
> +
> +#define __arm_smccc_1_1_call(fn, inst, ...) \
> +	CONCATENATE(__arm_smccc_1_1_call_, COUNT_ARGS(__VA_ARGS__))(fn, inst, __VA_ARGS__)
> +#else
> +#define __arm_smccc_1_1_call(fn, inst, ...) \
> +	__arm_smccc_1_1(inst, __VA_ARGS__)
> +#endif
> +
>  /*
>   * arm_smccc_1_1_smc() - make an SMCCC v1.1 compliant SMC call
>   *
> @@ -654,7 +687,8 @@ asmlinkage void __arm_smccc_hvc(unsigned long a0, unsigned long a1,
>   * to the SMC instruction. The return values are updated with the content
>   * from register 0 to 3 on return from the SMC instruction if not NULL.
>   */
> -#define arm_smccc_1_1_smc(...)	__arm_smccc_1_1(SMCCC_SMC_INST, __VA_ARGS__)
> +#define arm_smccc_1_1_smc(...) \
> +	__arm_smccc_1_1_call(arm_smccc_smc, SMCCC_SMC_INST, __VA_ARGS__)
>  
>  /*
>   * arm_smccc_1_1_hvc() - make an SMCCC v1.1 compliant HVC call
> @@ -670,14 +704,15 @@ asmlinkage void __arm_smccc_hvc(unsigned long a0, unsigned long a1,
>   * to the HVC instruction. The return values are updated with the content
>   * from register 0 to 3 on return from the HVC instruction if not NULL.
>   */
> -#define arm_smccc_1_1_hvc(...)	__arm_smccc_1_1(SMCCC_HVC_INST, __VA_ARGS__)
> +#define arm_smccc_1_1_hvc(...) \
> +	__arm_smccc_1_1_call(arm_smccc_hvc, SMCCC_HVC_INST, __VA_ARGS__)
>  
>  /*
>   * Like arm_smccc_1_1* but always returns SMCCC_RET_NOT_SUPPORTED.
>   * Used when the SMCCC conduit is not defined. The empty asm statement
>   * avoids compiler warnings about unused variables.
>   */
> -#define __fail_smccc_1_1(...)						\
> +#define __fail_smccc_1_1_inline(...)					\
>  	do {								\
>  		CONCATENATE(__declare_arg_,				\
>  			    COUNT_ARGS(__VA_ARGS__))(__VA_ARGS__);	\
> @@ -689,6 +724,38 @@ asmlinkage void __arm_smccc_hvc(unsigned long a0, unsigned long a1,
>  			___res->a0 = SMCCC_RET_NOT_SUPPORTED;		\
>  	} while (0)
>  
> +#if defined(CONFIG_ARM) && defined(CONFIG_THUMB2_KERNEL)
> +#define __fail_smccc_1_1_no_regs(_a0, _a1, _a2, _a3, _a4, _a5, _a6, _a7, res) \
> +	do {\
> +		struct arm_smccc_res *__res_ptr = (res);\
> +\
> +		(void)(_a0);\
> +		(void)(_a1);\
> +		(void)(_a2);\
> +		(void)(_a3);\
> +		(void)(_a4);\
> +		(void)(_a5);\
> +		(void)(_a6);\
> +		(void)(_a7);\
> +		if (__res_ptr)\
> +			__res_ptr->a0 = SMCCC_RET_NOT_SUPPORTED;\
> +	} while (0)
> +
> +#define __fail_smccc_1_1_2 __fail_smccc_1_1_inline
> +#define __fail_smccc_1_1_3 __fail_smccc_1_1_inline
> +#define __fail_smccc_1_1_4 __fail_smccc_1_1_inline
> +#define __fail_smccc_1_1_5 __fail_smccc_1_1_inline
> +#define __fail_smccc_1_1_6 __fail_smccc_1_1_inline
> +#define __fail_smccc_1_1_7 __fail_smccc_1_1_inline
> +#define __fail_smccc_1_1_8 __fail_smccc_1_1_inline
> +#define __fail_smccc_1_1_9 __fail_smccc_1_1_no_regs
> +
> +#define __fail_smccc_1_1(...) \
> +	CONCATENATE(__fail_smccc_1_1_, COUNT_ARGS(__VA_ARGS__))(__VA_ARGS__)
> +#else
> +#define __fail_smccc_1_1(...)	__fail_smccc_1_1_inline(__VA_ARGS__)
> +#endif
> +
>  /*
>   * arm_smccc_1_1_invoke() - make an SMCCC v1.1 compliant call
>   *