Hotswap works in MAME (once)!

asm/asm.fnl

@@ -251,15 +251,16 @@
        (set self.dbgfile nil))
      self)
    :read-hotswap
-   (fn [self machine]
+   (fn [self machine prg-new]
      (let [addr-to-label {}
            addr-to-size {}]
        (each [_ block (pairs self.org-to-block)]
          (each [label pdat (pairs block.preserved)]
            (tset addr-to-label pdat.addr label)
            (tset addr-to-size pdat.addr pdat.size)))
-       (collect [addr bytes (pairs (machine:read-batch addr-to-size))]
+       (lume.merge (collect [addr bytes (pairs (machine:read-batch addr-to-size))]
-         (values (. addr-to-label addr) bytes))))
+                     (values (. addr-to-label addr) bytes))
+                   (if (?. self.source :read-hotswap) (self.source:read-hotswap machine prg-new) {}))))
    :write-hotswap
    (fn [self machine hotswap]
      (machine:write-batch

link/mame.fnl

@@ -174,7 +174,7 @@
   (self:set-bp addr
     #(util.in-coro (fn []
        (self:clear-bp addr)
-       (local hotswap (prg-old:read-hotswap self))
+       (local hotswap (prg-old:read-hotswap self prg-new))
        (prg-new:upload self)
        (prg-new:write-hotswap self hotswap)
        (self:jump (prg-new:lookup-addr :on-hotswap))

ssc/hotswap.fnl

@@ -0,0 +1,119 @@
+; hotswap support
+(local {: addr-parser} (require :asm.65816))
+(local util (require :lib.util))
+(local {: bytes-to-uint16 : bytes-to-uint24 : int16-to-bytes : int24-to-bytes} util)
+
+; Hotswap theory:
+; The common case is code moving around in memory; even if you are not changing the content of code that
+; is currently executing, any changes to anything mean that pointers to that code will need to change.
+; If you try not to store pointers in globals (when everything is statically allocated, you should explicitly
+; name things, like in Forth) then the main place that persistent pointers to code exist is in call stacks -
+; specifically, the values on the stack consumed by "rts" or "rtl". When hotswapping, we need to walk the
+; callstack and A. find these values, and B. patch them to their new values. For this, we need to be able to
+; map any address that might be returned to from the old program to the new program - we can easily do this
+; by generating symbols for each callsite and setting up a reverse lookup table. We _also_ need to know the
+; stack layout at the time of each call so that we can find the next link in the chain, and to verify that
+; this hasn't changed (if the function has changed enough, then we can't modify it mid-execution).
+
+(fn assert-local-matches [funcname loc-old loc-new]
+  (each [_ key (ipairs [:type :name :returnaddr])]
+    (assert (= (. loc-old key) (. loc-new key)) (.. "Stack mismatch when patching " funcname))))
+
+(fn assert-locals-match [funcname locals-old locals-new]
+  (assert (= (length locals-old) (length locals-new)) (.. "Stack size mismatch when patching " funcname))
+  (each [iloc loc-old (ipairs locals-old)]
+    (assert-local-matches funcname loc-old (. locals-new iloc))))
+
+(fn next-callsite-offset [locals]
+  (var offset 0)
+  (var start-counting false)
+  (each [_ loc (ipairs locals)]
+    (if start-counting (let [size (match loc.type :placeholder 0 :word 2 :long 4)] (set offset (+ offset size)))
+        loc.returnaddr (set start-counting true)))
+  offset)
+
+(fn next-callsite-far? [locals]
+  (var far? false)
+  (each [_ loc (ipairs locals)]
+    (when (and loc.returnaddr (= loc.type :long))
+      (set far? true)))
+  far?)
+
+(fn read-callsite-addr [stack bank far]
+  (if far (bytes-to-uint24 stack 1) ; lowest byte (top of stack) is preserved B register
+          (bit.bor (bytes-to-uint16 stack) (bit.lshift bank 16))))
+
+(fn lookup-callsite [ssc addr]
+  (if (= addr (- (ssc.prg:lookup-addr :yield-forever) 1))
+      {:callsite-sym :yield-forever :locals [] :calling :yield-forever :funcname "<base task>"}
+    (. ssc.addr-to-callsite addr)))
+
+(fn patch-stack [ssc-old ssc-new stack bank far]
+  (print (length stack) bank far)
+  (if (= (length stack) 0) stack
+      ; top-of-stack should be a callsite; look it up
+    (let [callsite-addr (read-callsite-addr stack bank far)
+          {: callsite-sym : locals : funcname} (assert (lookup-callsite ssc-old callsite-addr)
+                                                 (.. "Top of stack value " callsite-addr " is not a recognized callsite"))
+          new-addr (- (ssc-new.prg:lookup-addr callsite-sym) 1)
+          {:locals new-locals} (lookup-callsite ssc-new  new-addr)
+          new-bank (bit.rshift new-addr 16)
+          _ (when (not far) (assert (= (bit.band callsite-addr 0xff0000) (bit.band new-addr 0xff0000))
+                              (.. funcname " moved banks from " bank " to " new-bank)))
+          _ (print (.. "patching " callsite-sym " from " callsite-addr " to " new-addr))
+          _ (assert-locals-match funcname locals new-locals)
+          new-top (if far (.. (stack:sub 1 1) (int24-to-bytes new-addr))
+                          (int16-to-bytes new-addr))
+          iaftertop (if far 5 3)
+          inextstack (+ iaftertop (next-callsite-offset locals))
+          _ (print (.. "locals " (fv locals) " offset " (next-callsite-offset locals)) inextstack)]
+      (.. new-top (stack:sub iaftertop (- inextstack 1))
+          (if (= funcname ssc-old.prg.start-symbol) (stack:sub inextstack) ; stop when we hit the boot-up function
+            (patch-stack ssc-old ssc-new (stack:sub inextstack) new-bank (next-callsite-far? locals)))))))
+
+(fn split-equally [s size]
+  (values (fn [s iprev] (let [i (+ iprev 1)
+                              istart (+ (* (- i 1) size) 1)
+                              iend (* i size)]
+                          (when (>= (length s) iend) (values i (s:sub istart iend)))))
+          s 0))
+
+(fn read-stacks [link ssc]
+  (let [stack-bounds-addr (ssc.prg:lookup-addr :first-task)
+        stack-bounds-bytes (link:read stack-bounds-addr 4)
+        first-task (bytes-to-uint16 stack-bounds-bytes)
+        last-task (bytes-to-uint16 stack-bounds-bytes 2)
+        task-size 0x100
+        read-size (+ (- last-task first-task) task-size)
+        task-count (/ read-size task-size)
+        task-bytes (link:read first-task read-size)
+        sp-offset (addr-parser ssc.TASK-STACK)]
+    (icollect [_ task (split-equally task-bytes task-size)]
+      (let [sp-addr (bytes-to-uint16 task sp-offset)
+            istackstart (bit.band sp-addr 0xff)
+            stack (task:sub (+ istackstart 2))]
+        {:sp-addr (+ sp-addr 1) : stack}))))
+
+(fn lookup-yield-bank [ssc] (bit.rshift (ssc.prg:lookup-addr :yield) 16))
+(fn filter-nonyielding-stacks [ssc stacks]
+  (let [yield-bank (lookup-yield-bank ssc)]
+    (print "yield-bank" yield-bank)
+    (icollect [_ stack (ipairs stacks)]
+      (let [callsite-addr (read-callsite-addr stack.stack yield-bank false)
+            callsite (lookup-callsite ssc callsite-addr)
+            funcname (?. callsite :calling)]
+        (print "top callsite:" (string.format "%X" callsite-addr) (fv callsite))
+        (when (= funcname :yield) stack)))))
+
+(fn hotswap-stacks [link ssc-old ssc-new]
+  (print "hotswappin time" link ssc-old ssc-new)
+  (let [stacks (read-stacks link ssc-old)
+        _ (print "read stacks" (fv stacks))
+        yielding-stacks (filter-nonyielding-stacks ssc-old stacks)]
+    (print "filtered stacks" (length stacks) (length yielding-stacks))
+    (collect [_ {: sp-addr : stack} (ipairs yielding-stacks)]
+      (let [(success new-stack) (pcall #(patch-stack ssc-old ssc-new stack (lookup-yield-bank ssc-old) false))]
+        (if success (do (print "patched" (stack:tohex) "to" (new-stack:tohex)) (values (tostring sp-addr) new-stack))
+          (error (.. new-stack ": stack at " (string.format "%X" sp-addr))))))))
+
+{: hotswap-stacks}

ssc/iigs/bootstub.fnl

@@ -3,13 +3,16 @@
 
 #(compile $1
    (start-symbol boot)
+   (predef-fn boot () void far)
+   (predef-fn [(or $2 :main)] () void far)
+
    [(when (not= link.name :udpdebug) (! (do ;udpdebug boots into 16-bit mode
      (start-symbol boot-8)
      (org 0x1000)
      (fn boot-8 ()
-       (asm (clc) (xce) (rep 0x30)  ; disable emulation mode, 16-bit index registers
+       (asm (clc) (xce) (rep 0x30))  ; disable emulation mode, 16-bit index registers
-            (jsr boot)
+       (boot)
-            (sec) (xce))) ; re-enter emulation mode
+       (asm (sec) (xce))) ; re-enter emulation mode
    )))]
 
    (org 0x060000)
@@ -42,7 +45,7 @@
      (set! BootHandle-e0 (NewHandle 0x4000 BootUserID 0xb017 0xe02000))
      (set! BootHandle-e1 (NewHandle 0x8000 BootUserID 0xb017 0xe12000))
 
-     (asm (jsl [(or $2 :main)]))
+     ( [(or $2 :main)] )
 
      (DisposeHandle BootHandle-e1)
      (DisposeHandle BootHandle-e0)

ssc/init.fnl

@@ -207,7 +207,7 @@
 
 (fn Ssc.compile-function-generic [self name args body post-body returnaddr-type call-instruction]
   (let [arglocals (self:parse-parameters args)]
-    (self:define-fn name (lume.concat arglocals [{:type returnaddr-type :comment :returnaddr}])
+    (self:define-fn name (lume.concat arglocals [{:type returnaddr-type :returnaddr true}])
       #(let [(c-function etype) (self:expr-poly body)]
          (self.org:append name c-function (table.unpack post-body))
          {:arity (length args) :args arglocals :org self.org :type etype : name : call-instruction}))))
@@ -482,8 +482,9 @@
         locals (lume.clone self.locals)
         callid (or (. self.callsites f.name) 0)
         _ (tset self.callsites f.name (+ callid 1))
-        callsite-sym (.. "<callsite " self.defining-fn " " f.name ":" callid ">")
+        funcname self.defining-fn
-        capture-addr (fn [addr] (tset self.addr-to-callsite addr {: callsite-sym : locals}))
+        callsite-sym (.. "<callsite " funcname " " f.name ":" callid ">")
+        capture-addr (fn [addr] (tset self.addr-to-callsite (- addr 1) {: callsite-sym : locals : funcname :calling f.name}))
         post (icollect [_ (countiter (length args))] (self:drop))]
     (values (lume.concat [:block] pre [[f.call-instruction f.name] callsite-sym [:export callsite-sym] [:meta capture-addr]] post) f.type)))
 
@@ -541,6 +542,11 @@
 
 (fn Ssc.assemble [self]
   (self.prg:assemble)
+  (set self.prg.source self)
   self.prg)
 
+(fn Ssc.read-hotswap [self machine prg-new]
+  (local {: hotswap-stacks} (require :ssc.hotswap))
+  (hotswap-stacks machine self prg-new.source))
+
 Ssc

ssc/task.fnl

@@ -24,7 +24,8 @@
             [:tsc] [:and 0xff] [:ora task-base] [:tcs]])])
 
   (fn yield ()
-    (asm (tsc) (sta [$1.TASK-STACK])
+    (asm (tsc) (sta [$1.TASK-STACK]) ;  
+         debug-stub on-hotswap (export debug-stub) (export on-hotswap) ; todo: cleanup mame hotswap logic
          (lda [$1.TASK-NEXT]) (tcd)
          (lda [$1.TASK-STACK]) (tcs)))