[go-nuts] maptype questions

[Bill Morgan]

for this code:

m := make(map[int]int, 9)

I think the compiler creates a maptype that is stored at type.*+60480(SB) 
that it uses for the call to runtime.makemap:

m := make(map[int]int, 9)
  0x10d0b81 488d05f8ec LEAQ type.*+60480(SB), AX 
  0x10d0b88 48890424 MOVQ AX, 0(SP) 
  0x10d0b8c 48c74424080900 MOVQ $0x9, 0x8(SP) 
  0x10d0b95 48c7442410 MOVQ $0x0, 0x10(SP) 
  0x10d0b9e 6690 NOPW 
  0x10d0ba0 e8fbdff3ff CALL runtime.makemap(SB) 

Where is the code in the compiler that creates the maptype? I'm wondering 
how the bucket size is computed and how the rest of the maptype structure 
is filled out.

Is there a way to print out the type info stored in the binary?

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[go-nuts] who is mike?

[Bill Morgan]

who is mike wrt this commit?

commit bc0b4f0d2a610059afb95ef0360704714815187d
Author: Ken Thompson 
Date:   Thu Nov 13 10:35:44 2008 -0800

mike's map code

R=r
OCL=19146
CL=19146

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[go-nuts] Re: [runtime] gostring question

[Bill Morgan]

On Tuesday, June 23, 2020 at 7:32:56 PM UTC-5, Bill Morgan wrote:
>
> I'm a C programmer so maybe this is a dumb question but, why does this 
> code in runtime/gostring.go allocate (rawstring) then copy data (memmove) 
> instead of just making the stringStruct.str point at the incoming data? 
> i.e. copy the pointer instead of allocating+copying data.
>
>
> func gostring(p *byte) string {
> l := findnull(p)
> if l == 0 {
> return ""
> }
> s, b := rawstring(l)
> memmove(unsafe.Pointer([0]), unsafe.Pointer(p), uintptr(l))
> return s
> }
>


looks like the code came from 
commit: 61dca94e107170d2ff3beb13bb9fa5ce49d8d6fd and the old string.c file 
had a gostringnocopy that copied the ptr instead of allocating and copying. 

Wondering why that was removed. I guess there must be some reason that you 
must have a duplicate copy.

 

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[go-nuts] [runtime] gostring question

[Bill Morgan]

I'm a C programmer so maybe this is a dumb question but, why does this code 
in runtime/gostring.go allocate (rawstring) then copy data (memmove) 
instead of just making the stringStruct.str point at the incoming data? 
i.e. copy the pointer instead of allocating+copying data.


func gostring(p *byte) string {
l := findnull(p)
if l == 0 {
return ""
}
s, b := rawstring(l)
memmove(unsafe.Pointer([0]), unsafe.Pointer(p), uintptr(l))
return s
}

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