about golang defer?

[xie cui]

a defer call generate some code like:

• • v42 (8) = StaticLECall <mem> {AuxCall{runtime.deferprocStack}} [8] v36 v41
  • v43 (8) = SelectN <mem> [0] v42
• Defer v42 → b2 b3 (likely) (8)

• b2: ← b1-
• • v48 (7) = Copy <mem> v43
  • v49 (7) = VarKill <mem> {.autotmp_0} v48
  • v50 (9) = StaticLECall <mem> {AuxCall{runtime.deferreturn}} v49
  • v51 (9) = SelectN <mem> [0] v50
  • v52 (9) = MakeResult <mem> v51
• Ret v52 (9)

• b3: ← b1-
• • v44 (8) = Copy <mem> v43
  • v45 (8) = StaticLECall <mem> {AuxCall{runtime.deferreturn}} v44
  • v46 (8) = SelectN <mem> [0] v45
  • v47 (8) = MakeResult <mem> v46
• Ret v47 (8)

my question is Under what circumstances the deferprocStack return 1?

some useful info： 

https://github.com/golang/go/blob/master/src/cmd/compile/internal/amd64/ssa.go#L1287-L1289

https://github.com/golang/go/blob/master/src/runtime/panic.go#L290-L328, in these lines it seems deferprocStack always return 0. i think i have miss some thing, please help me to find when it get to branch return 1.

[jake...@gmail.com]

I can't help you with your specific question, but two procedural points. First, while such a question is welcome in this group (golang-nuts), you may reach an audience better able to answer it on the golang-dev group, since it deals with the internal details of the compiler. But I would also note that golang-dev is in "Quiet Week", so will be less active than normal.

However you proceed, I hope you get an answer.

[Ian Lance Taylor]

deferprocStack will appear to return 1 if the deferred function calls
recover. This is implemented by the function "recovery" in
runtime/panic.go, which resets the program counter and stack pointer
and sets the return register to 1.

Ian