fix: non-page code overflow into kernel-reserved I/O space

.vscode/settings.json

@@ -0,0 +1,5 @@
+{
+  "cSpell.words": [
+    "endlogical"
+  ]
+}

modules/_scripts/makebuild.py

@@ -11,14 +11,24 @@
 
 import os
 import re
-import sys
 from pathlib import Path
 from typing import TextIO
 
 # regex for exported labels
 export_re = re.compile(r"^\s*Export_(\w+)\s*:\s*(;.*)?$")
 
 
+PAGE2_BEGIN = """
+.section page2
+.logical * + $2000
+"""
+
+PAGE2_END = """
+.endlogical
+.send page2
+"""
+
+
 def main(*, module_name: str, build_dir: Path, page: int = 1) -> None:
     """Generate a single assembly build file for the specified module."""
     if not build_dir.exists():
@@ -59,26 +69,28 @@ def process_source(path: Path, out: TextIO, *, page: int = 1) -> list[str]:
             if page == 2:
                 normalized = " ".join(line.split())
                 if normalized == ".section code":
-                    out.write("\t\t.section page2\n")
-                    out.write("\t\t.logical * + $2000\n")
+                    out.write(PAGE2_BEGIN)
                     continue
                 elif normalized == ".send code":
-                    out.write("\t\t.here\n")
-                    out.write("\t\t.send page2\n")
+                    out.write(PAGE2_END)
                     continue
 
             out.write(f"{line.rstrip()}\n")
 
     return exports
 
 
-def dump_exports(build_dir: Path, module_name: str, exports: list[str], *, page: int = 1) -> None:
+def dump_exports(
+    build_dir: Path, module_name: str, exports: list[str], *, page: int = 1
+) -> None:
     """Save module exports to the corresponding `.exports` file."""
     if not exports:
         return
 
     suffix = "_p2" if page == 2 else ""
-    with open(build_dir / (module_name + suffix + ".exports"), "w", encoding="utf-8") as out:
+    with open(
+        build_dir / (module_name + suffix + ".exports"), "w", encoding="utf-8"
+    ) as out:
         for export in exports:
             out.write(f"{export}\n")
 
@@ -109,8 +121,12 @@ def collect_sources(module_name: str) -> list[Path]:
 
     parser = argparse.ArgumentParser(description="Build module assembly file")
     parser.add_argument("module_name", help="Name of the module to build")
-    parser.add_argument("build_dir", nargs="?", default=".build", help="Build output directory")
-    parser.add_argument("--page", type=int, default=1, choices=[1, 2], help="Module page (1 or 2)")
+    parser.add_argument(
+        "build_dir", nargs="?", default=".build", help="Build output directory"
+    )
+    parser.add_argument(
+        "--page", type=int, default=1, choices=[1, 2], help="Module page (1 or 2)"
+    )
     args = parser.parse_args()
 
     main(

modules/_scripts/makeexport.py

@@ -22,48 +22,7 @@ def main(*, build_dir: Path) -> None:
     print(f"PagingEnabled = {1 if paging else 0}")
 
     has_page2 = any(exports[m]["page"] == 2 for m in exports)
-
-    if paging and has_page2:
-        # These routines are included inside an existing .section code block
-        # in 00start.asm, so no .section/.send wrappers are needed here.
-        # Slot3ModulePage/Slot3Depth/Slot3Saved are declared in 04data.inc
-        # (placed before numberBuffer/decimalBuffer to survive buffer overflows).
-        print("")
-        print("; --- Slot 3 module bank switching ---")
-        print("")
-        print("Slot3Init:")
-        print("\tstz Slot3Depth")
-        print("\tlda 8+4")
-        print("\tclc")
-        print("\tadc #3")
-        print("\tsta Slot3ModulePage")
-        print("\trts")
-        print("")
-        print("Slot3BankIn:")
-        print("\tphy")
-        print("\tpha")
-        print("\tinc Slot3Depth")
-        print("\tlda Slot3Depth")
-        print("\tcmp #1")
-        print("\tbne +")
-        print("\tldy 8+3")
-        print("\tsty Slot3Saved")
-        print("\tldy Slot3ModulePage")
-        print("\tsty 8+3")
-        print("+\tpla")
-        print("\tply")
-        print("\trts")
-        print("")
-        print("Slot3BankOut:")
-        print("\tpha")
-        print("\tphy")
-        print("\tdec Slot3Depth")
-        print("\tbne +")
-        print("\tldy Slot3Saved")
-        print("\tsty 8+3")
-        print("+\tply")
-        print("\tpla")
-        print("\trts")
+    print(f"HasPage2 = {1 if has_page2 else 0}")
 
     for module in exports:
         page = exports[module]["page"]
@@ -74,25 +33,39 @@ def main(*, build_dir: Path) -> None:
             print(f"{routine}:")
             if paging:
                 if page == 1:
-                    print("\tinc 8+5")
-                    print(f"\tjsr\tExport_{routine}")
-                    print("\tphp")
-                    print("\tdec 8+5")
-                    print("\tplp")
-                    print("\trts")
+                    print(page1_thunk(routine))
                 elif page == 2:
-                    print("\tjsr Slot3BankIn")
-                    print(f"\tjsr\tExport_{routine}")
-                    print("\tphp")
-                    print("\tjsr Slot3BankOut")
-                    print("\tplp")
-                    print("\trts")
+                    print(page2_thunk(routine))
+                else:
+                    raise RuntimeError(f"Unknown page #{page}")
             else:
                 print(f"\tjmp\tExport_{routine}")
 
         print("\t.endif")
 
 
+def page1_thunk(routine: str) -> str:
+    return f"""
+    inc 8+5
+    jsr Export_{routine}
+    php
+    dec 8+5
+    plp
+    rts
+"""
+
+
+def page2_thunk(routine: str) -> str:
+    return f"""
+    jsr Slot3BankIn
+    jsr Export_{routine}
+    php
+    jsr Slot3BankOut
+    plp
+    rts
+"""
+
+
 def read_exports(build_dir: Path) -> dict[str, dict]:
     """Read all `.exports` files from the build directory.
 

source/_basic.asm

@@ -159,16 +159,25 @@
 
 
 .section code
+    ; issuing a warning instead of an error so one can examine output listing for details
+    .cwarn * > $C000, "BROKEN BUILD: non-paged code overflows into kernel-reserved I/O space ($C000-$DFFF) by ", * - $C000," bytes"
+
 StartModuleCode:
-	.if PagingEnabled==1
-	* = $A000
-	.offs $2000
-	.endif
+    .if PagingEnabled==1
+        * = $A000
+        .offs $2000
+    .endif
 .send code
+
 	.include	"../modules/.build/hardware.module.asm"
 	.include	"../modules/.build/tokeniser.module.asm"
 	.include	"../modules/.build/graphics.module.asm"
 
+.section code
+    ; issuing a warning instead of an error so one can examine output listing for details
+    .cwarn * > $C000, "BROKEN BUILD: page 1 code overflows into kernel-reserved I/O space ($C000-$DFFF) by ", * - $C000," bytes"
+.send code
+
 ; --- Startup banner data in boot section ($6000-$7FFF) ---
 	.include	"../modules/hardware/startup/.build/banner.dat"
 
@@ -180,3 +189,10 @@ StartModuleCode:
 	.include	"./common/generated/_errortext_p2.asm"
 	.include	"../modules/.build/kernel_p2.module.asm"
 	.include	"../modules/.build/sound_p2.module.asm"
+
+.section page2
+.logical * + $2000
+    ; issuing a warning instead of an error so one can examine output listing for details
+    .cwarn * > $8000, "BROKEN BUILD: page 2 code overflows into SuperBASIC ROM space ($8000-$BFFF) by ", * - $8000," bytes"
+.endlogical
+.send page2

source/common/aa.system/00start.asm

@@ -33,6 +33,7 @@ KernelHeader:
 ;;
 Boot:	jmp 	Start
 		.include "../../../modules/.build/_exports.module.asm"
+		.include "./_slot3banking.asm"
 
 Start:	ldx 	#$FF 						; stack reset
 		txs
@@ -45,11 +46,12 @@ Start:	ldx 	#$FF 						; stack reset
 
 		jsr 	EXTInitialize 				; hardware initialization
 		jsr 	EXTShowStartupBanner        ; reads banner data from slot 3
-		jsr 	DisplayBannerText           ; print hardware, ROM & build info
 
 		lda 	#3 							; remap slot 3 to RAM page 3
 		sta 	$0008+3 					; (frees $6000-$7FFF for arrays/temp buffers)
 
+		jsr 	DisplayBannerText           ; print hardware, ROM & build info
+
 		lda 	0  							; turn on editing of MMU LUT
 		ora 	#$80
 		sta 	0

source/common/aa.system/_slot3banking.asm

@@ -0,0 +1,48 @@
+;;
+; Slot 3 module bank switching
+;
+; Note that slot 3 (page 2) banking is about 4x slower than slot 5 (page 1),
+; ~29 cycles vs ~112 cycles per thunk.
+;
+; `Slot3ModulePage`, `Slot3Depth`, and `Slot3Saved` are declared in
+; `04data.inc` (placed before `numberBuffer`/`decimalBuffer` to survive
+; buffer overflows).
+;;
+
+.if PagingEnabled==1 && HasPage2==1
+
+Slot3Init:
+	stz Slot3Depth
+	lda 8+4
+	clc
+	adc #3
+	sta Slot3ModulePage
+	rts
+
+Slot3BankIn:
+	phy
+	pha
+	inc Slot3Depth
+	lda Slot3Depth
+	cmp #1
+	bne +
+	ldy 8+3
+	sty Slot3Saved
+	ldy Slot3ModulePage
+	sty 8+3
++	pla
+	ply
+	rts
+
+Slot3BankOut:
+	pha
+	phy
+	dec Slot3Depth
+	bne +
+	ldy Slot3Saved
+	sty 8+3
++	ply
+	pla
+	rts
+
+.endif

source/common/generated/_errortext.asm

@@ -1,6 +1,7 @@
 ;
 ;	This is automatically generated.
 ;
+
 .section code
 ErrorText:
 	.text	"Break",0

source/common/generated/_errortext_p2.asm

@@ -1,8 +1,9 @@
 ;
 ;	This is automatically generated.
 ;
-	.section page2
-	.logical * + $2000
+
+.section page2
+.logical * + $2000
 ErrorText:
 	.text	"Break",0
 	.text	"Syntax error",0
@@ -35,5 +36,5 @@ ErrorText:
 	.text	"Too many parameters",0
 	.text	"Formula too complex",0
 	.text	"Initialization error",0
-	.here
-	.send page2
+.endlogical
+.send page2