save context, when switch goroutine?

[xie cui]

as we know,  call function gogo can jump to other other goroutine. when goroutine1 switch to goroutine2 it must save the current context of goroutine1(sp pc. so). i can find the function runtime·gosave to save current context, but i cann't find where the code call gosave, can some explain when context switch where is the to call gosave, or maybe context save is in other code? 

if it call gosave to save context, what is the possible stack when call gosave?

[xie cui]

I find the mcall function!