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

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