[PATCH v5 resend 1/4] include: Define fast fail codes and the __fastfail() intrinsic.

[Jinoh Kang]

On 1/20/22 02:49, Thomas Faber wrote:
> Hi,
> 
> On 2022-01-19 12:06, Jinoh Kang wrote:
>> +#if defined(__GNUC__)
>> +#if defined(__x86_64__)
>> +static FORCEINLINE DECLSPEC_NORETURN void __fastfail(unsigned int code)
>> +{
>> +    register ULONGLONG val __asm__("rcx") = code;
>> +    __asm__ __volatile__( "int $0x29" :: "r" (val) : "memory" );
> 
> 
> Any reason to prefer this "manual move" into a register over specifying r/ecx as an input into the assembly block?

It's just a style preference, nothing much.  Since now that i see other code
seems to use specific-register constraints, perhaps I should follow that instead...

> I.e.
> 
> __asm__ __volatile__( "int $0x29" :: "c" ((ULONG_PTR)code) : "memory" );
> 
> As an added bonus, that would make the function identical between x64 and x86.
> (The cast to ULONG_PTR is to make the compiler aware that the upper bits of rcx _must_ be zero, rather than just letting it happen incidentally.)
> 
> Something similar might be applicable to ARM, too, but I'm not sure.

There's no such thing as specific-register constraints in ARM/ARM64.

> 
> Thanks,
> Thomas
> 


-- 
Sincerely,
Jinoh Kang