runtime.mcall source code

[yao shucai]

Hi there,

I am reading the source code of the golang recently. I understand the functionality of the mcall except one line code(asm_amd64.s : 184):

183:    PUSHQ AX

184: MOVQ DI, DX

MOVQ 0(DI), DI

CALL DI

POPQ AX

I can't figure out why do we need to move DI to DX? Is there any special purpose of this instruction? 

Thanks!

Shucai

[Ian Lance Taylor]

In Go a function pointer points to a block of memory whose first word
contains a pointer to the actual code and whose subsequent words
contain the function closure (see https://golang.org/s/go11func).
When calling the function, a pointer to that block of memory is always
passed in a special register, so that the function can access its
closure if necessary. On amd64, the closure pointer is passed in the
DX register.

Ian

[yao shucai]

Get it. Thank you very much!

Shucai