Definitive guide to go-c and go-asm

[Pawel Kraszewski]

Hello!
Is there any guide to go-asm? Esspecially for the go ABI: how to pass arguments, how to return results, which registers to preserve, etc. Source code of packages math and syscall helps slightly, but is not enough for my project.

The cgo solution with embedded assembly gives way too much overhead. I managed to implement RDTSC both via direct asm and via cgo - the difference is overwhelming. Call-to-call in go-asm gives avg 90 cycles while in cgo-asm about 1300 cycles...

Moreover, is there a way to allocate memory with specific alignment (16 bytes to be precise) ? One solution I see is to allocate it in cgo and pass back as unsafe.Pointer. Is this the way?

All this is necessary for me to implement ultra low latency interface to Via Padlock cryptographic coprocessor.

[Aram Hăvărneanu]

http://tip.golang.org/doc/asm

--
Aram Hăvărneanu

[Gustavo Niemeyer]

On Tue, Nov 19, 2013 at 3:20 PM, Pawel Kraszewski <pa...@kraszewscy.net> wrote:
> Moreover, is there a way to allocate memory with specific alignment (16 bytes to be precise) ? One solution I see is to allocate it in cgo and pass back as unsafe.Pointer. Is this the way?

You can always align it yourself by allocating 15 bytes more than you
need and sliding the start as necessary.


gustavo @ http://niemeyer.net

[Pawel Kraszewski]

Thanks for valuable answers.

+Aram: How did you find this? I'm travelling the Go docs all the way across for the last few days - but asm guide didn't catch my eye...

+Gustavo: Yes, I know overallocation technique. I just hoped to have some sort of __aligned__ equivalent. Obvious problem is that Go has no pointer arithmetic to snap to the 16 boundary, so this leaves the unsafe.Pointer manipulations as a way to go.

Best regards

[Gustavo Niemeyer]

On Tue, Nov 19, 2013 at 6:50 PM, Pawel Kraszewski <pa...@kraszewscy.net> wrote:
> +Gustavo: Yes, I know overallocation technique. I just hoped to have some
> sort of __aligned__ equivalent. Obvious problem is that Go has no pointer
> arithmetic to snap to the 16 boundary, so this leaves the unsafe.Pointer
> manipulations as a way to go.

unsafe.Pointer != cgo, which was your actual suggestion.


gustavo @ http://niemeyer.net

[Dan Kortschak]

On Tue, 2013-11-19 at 12:50 -0800, Pawel Kraszewski wrote:
> +Aram: How did you find this? I'm travelling the Go docs all the way
> across for the last few days - but asm guide didn't catch my eye...

It's a very recent addition (note it's in tip).