Re: [for-4.20][PATCH 2/2] xen/arm: Fix build issue when CONFIG_PHYS_ADDR_T_32=y

[Michal Orzel <michal.orzel@xxxxxxx>]

On 27/01/2025 18:03, Alejandro Vallejo wrote:
> 
> 
> Hi,
> 
> On Mon Jan 27, 2025 at 10:45 AM GMT, Michal Orzel wrote:
>> On Arm32, when CONFIG_PHYS_ADDR_T_32 is set, a build failure is observed:
>> arch/arm/platforms/vexpress.c: In function 'vexpress_smp_init':
>> arch/arm/platforms/vexpress.c:102:12: error: format '%lx' expects argument 
>> of type 'long unsigned int', but argument 2 has type 'long long unsigned 
>> int' [-Werror=format=]
>>   102 |     printk("Set SYS_FLAGS to %"PRIpaddr" (%p)\n",
>>
>> When CONFIG_PHYS_ADDR_T_32 is set, paddr_t is defined as unsigned long.
>> Commit 96f35de69e59 dropped __virt_to_maddr() which used paddr_t as a
>> return type. Without a cast, the expression type is unsigned long long
>> which causes the issue. Fix it.
>>
>> Fixes: 96f35de69e59 ("x86+Arm: drop (rename) __virt_to_maddr() / 
>> __maddr_to_virt()")
>> Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
>> ---
>>  xen/arch/arm/include/asm/mm.h | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/xen/arch/arm/include/asm/mm.h b/xen/arch/arm/include/asm/mm.h
>> index f91ff088f6b1..a0d8e5afe977 100644
>> --- a/xen/arch/arm/include/asm/mm.h
>> +++ b/xen/arch/arm/include/asm/mm.h
>> @@ -263,7 +263,7 @@ static inline void __iomem *ioremap_wc(paddr_t start, 
>> size_t len)
>>
>>  #define virt_to_maddr(va) ({                                        \
>>      vaddr_t va_ = (vaddr_t)(va);                                    \
>> -    (va_to_par(va_) & PADDR_MASK & PAGE_MASK) | (va_ & ~PAGE_MASK); \
>> +    (paddr_t)((va_to_par(va_) & PADDR_MASK & PAGE_MASK) | (va_ & 
>> ~PAGE_MASK)); \
>>  })
>>
>>  #ifdef CONFIG_ARM_32
> 
> Out of curiosity, why not make va_to_par() and __va_to_par() return paddr_t
> rather than uint64_t? Then this cast would be unnecessary and the expression
> end up as unsigned long.
> 
> That would also cover any other uses outside this macro.
> 
> Unless I'm missing something else...
va_to_par() returns uint64_t because PAR_EL1 on Arm64 or PAR on Arm32 system 
registers are both 64bit.
So, it would not make sense (also it would be confusing) for va_to_par() to 
return already casted value.
The function ends with _par so it should reflect the register size as the name 
suggests. Macro is there
to cast this value as it also takes into account PADDR_MASK and PAGE_MASK.

~Michal