On 09/22/15 01:41, David Chisnall wrote:
> On 21 Sep 2015, at 21:45, H.J. Lu via cfe-dev <cfe-...@lists.llvm.org> wrote:
>>
>> The main purpose of x86 interrupt attribute is to allow programmers
>> to write x86 interrupt/exception handlers in C WITHOUT assembly
>> stubs to avoid extra branch from assembly stubs to C functions. I
>> want to keep the number of new intrinsics to minimum without sacrificing
>> handler performance. I leave faking error code in interrupt handler to
>> the programmer.
>
> The assembly stubs have to come from somewhere. You either put them
> in an assembly file (most people doing embedded x86 stuff steal the
> ones from NetBSD), or you put them in the compiler where they can be
> inlined. In terms of user interface, there’s not much difference in
> complexity. Having written this kind of code in the past, I can
> honestly say that using the assembly stubs was the least difficult
> part of getting them right. In terms of compiler complexity, there’s
> a big difference: in one case the compiler contains nothing, in the
> other it contains something special for a single use case. In terms
> of performance, the compiler version has the potential to be faster,
> but if we’re going to pay for the complexity then I think that we’d
> need to see some strong evidence that someone else is getting a
> noticeable benefit.
>
It is worth noting that most architectures has this support for a reason.
-hpa
