I don’t know the answer to this, but Alexis when you find out can I ask (I know I'm a broken record on this) that you write a Note to explain, with pointers from the various places you looked when you were trying to find out the answer?
Thanks!
Simon
| -----Original Message-----
| From: ghc-devs On Behalf Of Alexis King
| Sent: 14 February 2020 19:53
| To: ghc-devs
| Subject: Calling an unknown function from low-level Cmm
|
| Hi all,
|
| I’m trying to understand how to properly call an unknown function from
| low-level Cmm code. If I’m just applying a function to a state token, it’s
| easy; I can just do
|
| R1 = io;
| jump stg_ap_v_fast [R1];
|
| since the calling convention is consistent in that case. But what if my
| function takes actual arguments? I can’t do
|
| R1 = fun;
| R2 = arg;
| jump stg_ap_p_fast [R1, R2];
|
| because if the calling convention doesn’t pass any arguments in registers,
| that would be wrong. I could check if NO_ARG_REGS is defined and generate
| different code in that situation, but that seems extreme. One option I
| think would work would be to do
|
| R1 = fun;
| Sp_adj(-2);
| Sp(1) = arg;
| jump RET_LBL(stg_ap_p) [R1];
|
| but that seems wasteful if I have the argument in a register already
| anyway. Am I missing something?
|
| Thanks,
| Alexis
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