On Tuesday, September 20, 2016 at 11:00:34 AM UTC+8, Peng Gao wrote:
>
> BTW in your test file, you can directly append your bytes slice.
> b1 = append(b1, vs...)
> and slicesEqual is redundant, bytes.Equal does test the length of two
> arguments
>
I mix up cap and len, just ignore it.
>
> On Tuesday, September 20, 2016 at 6:56:55 AM UTC+8, Caleb Spare wrote:
>>
>> I'm trying to call a Go function from asm and I'm having trouble figuring
>> out the details.
>>
>> (In the past I've always endeavored to avoid this situation and make all
>> my asm functions be leaf functions, but in my current use case it would be
>> most helpful to be able to call a Go helper.)
>>
>> See the demo code at
>> https://github.com/cespare/misc/tree/master/asm/stackmap or go get
>> github.com/cespare/misc/asm/stackmap.
>>
>> For
>> the
>> demo, I have a small function with an append-style API:
>>
>> func X(b []byte) []byte
>>
>> This calls a Go helper growSlice.
>>
>> This code sometimes works, but if I run `go test -count 1000` I'll
>> quickly see
>>
>> runtime: frame github.com/cespare/misc/asm/stackmap.X untyped locals
>> 0xc420042bf8+0x30
>> fatal error: missing stackmap
>> ...
>>
>> I've read through the Runtime Coordination section of the
>> asm
>> walkthrough (https://golang.org/doc/asm#runtime) several times, but I
>> don't see the problem.
>>
>> Here is my understanding of a few relevant bits of that section (which
>> might be incorrect):
>>
>> If the results will hold live pointers during a call instruction, the
>>> function should start by zeroing the results and then executing the
>>> pseudo-instruction GO_RESULTS_INITIALIZED.
>>
>>
>> This doesn't seem to apply to my code because the results aren't
>> populated until after the CALL.
>>
>> If a function has no local stack frame, the pointer information can be
>>> omitted. This is indicated by a local frame size annotation of $0-n on the
>>> TEXT instruction. The pointer information can also be omitted if the
>>> function contains no call instructions. Otherwise, the local stack frame
>>> must not contain pointers, and the assembly must confirm this fact by
>>> executing the pseudo-instruction NO_LOCAL_POINTERS.
>>
>>
>> My function makes a CALL with arguments. But it has to have a pointer
>> (the slice) on the local stack frame in order to pass to that helper. I
>> don't really understand what this section means.
>>
>> `go vet` doesn't say anything about my code.
>>
>> Any ideas?
>>
>> Thanks!
>> Caleb
>>
>
--
You received this message because you are subscribed to the Google Groups
"golang-nuts" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to golang-nuts+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
