added ability to configure custom ASM launcher code in target configuration file

codeCore/src/prog8/code/core/ICompilationTarget.kt

@@ -34,6 +34,7 @@ interface ICompilationTarget: IStringEncoding, IMemSizer {
     var zeropage: Zeropage
     var golden: GoldenRam
     val libraryPath: Path?
+    val customLauncher: List<String>?
 
     fun initializeMemoryAreas(compilerOptions: CompilationOptions)
     fun getFloatAsmBytes(num: Number): String

codeCore/src/prog8/code/target/AtariTarget.kt

@@ -11,6 +11,7 @@ class AtariTarget: ICompilationTarget, IStringEncoding by Encoder, IMemSizer by
     override val name = NAME
     override val defaultEncoding = Encoding.ATASCII
     override val libraryPath = null
+    override val customLauncher = null
 
     companion object {
         const val NAME = "atari"

codeCore/src/prog8/code/target/C128Target.kt

@@ -18,6 +18,7 @@ class C128Target: ICompilationTarget, IStringEncoding by Encoder, IMemSizer by N
     override val name = NAME
     override val defaultEncoding = Encoding.PETSCII
     override val libraryPath = null
+    override val customLauncher = null
 
     companion object {
         const val NAME = "c128"

codeCore/src/prog8/code/target/C64Target.kt

@@ -11,6 +11,7 @@ class C64Target: ICompilationTarget, IStringEncoding by Encoder, IMemSizer by No
     override val name = NAME
     override val defaultEncoding = Encoding.PETSCII
     override val libraryPath = null
+    override val customLauncher = null
 
     companion object {
         const val NAME = "c64"

codeCore/src/prog8/code/target/ConfigFileTarget.kt

@@ -26,6 +26,7 @@ class ConfigFileTarget(
     override val BSSGOLDENRAM_START: UInt,
     override val BSSGOLDENRAM_END: UInt,
     override val libraryPath: Path,
+    override val customLauncher: List<String>?,
     val ioAddresses: List<UIntRange>,
     val zpScratchB1: UInt,
     val zpScratchReg: UInt,
@@ -101,6 +102,12 @@ class ConfigFileTarget(
             if(!libraryPath.isDirectory())
                 throw IOException("invalid library path: $libraryPath")
 
+            val customLauncherStr = props.getProperty("custom_launcher", null)
+            val customLauncher =
+                if(customLauncherStr?.isNotBlank()==true)
+                    (customLauncherStr+"\n").lines().map { it.trimEnd() }
+                else null
+
             return ConfigFileTarget(
                 configfile.nameWithoutExtension,
                 Encoding.entries.first { it.prefix==props.getString("encoding") },
@@ -114,6 +121,7 @@ class ConfigFileTarget(
                 props.getInteger("bss_goldenram_start"),
                 props.getInteger("bss_goldenram_end"),
                 libraryPath,
+                customLauncher,
                 ioAddresses,
                 props.getInteger("zp_scratch_b1"),
                 props.getInteger("zp_scratch_reg"),

codeCore/src/prog8/code/target/Cx16Target.kt

@@ -18,6 +18,7 @@ class Cx16Target: ICompilationTarget, IStringEncoding by Encoder, IMemSizer by N
     override val name = NAME
     override val defaultEncoding = Encoding.PETSCII
     override val libraryPath = null
+    override val customLauncher = null
 
     companion object {
         const val NAME = "cx16"

codeCore/src/prog8/code/target/Neo6502Target.kt

@@ -10,6 +10,7 @@ class Neo6502Target: ICompilationTarget, IStringEncoding by Encoder, IMemSizer b
     override val name = NAME
     override val defaultEncoding = Encoding.ISO
     override val libraryPath = null
+    override val customLauncher = null
 
     companion object {
         const val NAME = "neo"

codeCore/src/prog8/code/target/PETTarget.kt

@@ -18,6 +18,7 @@ class PETTarget: ICompilationTarget, IStringEncoding by Encoder, IMemSizer by No
     override val name = NAME
     override val defaultEncoding = Encoding.PETSCII
     override val libraryPath = null
+    override val customLauncher = null
 
     companion object {
         const val NAME = "pet32"

codeCore/src/prog8/code/target/VMTarget.kt

@@ -11,6 +11,7 @@ class VMTarget: ICompilationTarget, IStringEncoding by Encoder, IMemSizer by Nor
     override val name = NAME
     override val defaultEncoding = Encoding.ISO
     override val libraryPath = null
+    override val customLauncher = null
 
     companion object {
         const val NAME = "virtual"

codeGenCpu6502/src/prog8/codegen/cpu6502/ProgramAndVarsGen.kt

@@ -87,6 +87,16 @@ internal class ProgramAndVarsGen(
             }
         }
 
+        if(options.compTarget.customLauncher?.isNotEmpty()==true) {
+            asmgen.out("; ---- custom launcher assembler program ----")
+            asmgen.out("* = ${options.loadAddress.toHex()}")
+            asmgen.out("prog8_program_start\t; start of program label")
+            for(line in options.compTarget.customLauncher) {
+                asmgen.out(line)
+            }
+            return
+        }
+
         if(options.output == OutputType.LIBRARY) {
 
             asmgen.out("; ---- library assembler program ----")

docs/source/targetsystem.rst

@@ -52,6 +52,13 @@ You also need to create some essential ``syslib`` library module for the configu
 compiler won't have a built in library that can be used this time. The customtarget examples also show how to build
 the essentials.
 
+The target configuration file also allows you to override the entire launcher assembly fragment that the compiler
+usually puts at the start of the program (immediately after the setting of the program counter/load address and
+the program start label). This allows you to have full control over exactly what code or data bytes appear at
+the program's load address. But with great power comes great responsibility: you'll have to make sure you take
+care of some very low level Prog8 internals if you want to support stuff like the `exit` builtin function.
+Maybe the best thing is to look at the code generated by the compiler for an existing target and adapt that.
+
 
 Memory Model
 ============

examples/customtarget/tinyc64.properties

@@ -33,5 +33,9 @@ virtual_registers = $cfe0
 # Where can we find the standard library (syslib.p8). You can still add more paths manually using -srcdirs
 library = ./libraries/tinyc64
 
+# if a custom launcher string is supplied, the compiler won't output ANY launcher / init code by itself,
+# and instead outputs whatever is specified here. (You can use \n here for newline and \ for line continuantions)
+custom_launcher =
+
 # TODO should the 64tass arguments be in here too perhaps? So that the "program" parameter that now selects 1 of a few fixed sets of arguments, can be removed?
 # TODO should an emulator command line also be in here perhaps? So that -emu will work too.

examples/customtarget/tinycx16.properties

@@ -33,5 +33,9 @@ virtual_registers = $02
 # Where can we find the standard library (syslib.p8). You can still add more paths manually using -srcdirs
 library = ./libraries/tinycx16
 
+# if a custom launcher string is supplied, the compiler won't output ANY launcher / init code by itself,
+# and instead outputs whatever is specified here. (You can use \n here for newline and \ for line continuantions)
+custom_launcher =
+
 # TODO should the 64tass arguments be in here too perhaps? So that the "program" parameter that now selects 1 of a few fixed sets of arguments, can be removed?
 # TODO should an emulator command line also be in here perhaps? So that -emu will work too.

examples/customtarget/tinypet.properties

@@ -33,5 +33,9 @@ virtual_registers = $7fe0
 # Where can we find the standard library (syslib.p8). You can still add more paths manually using -srcdirs
 library = ./libraries/tinypet
 
+# if a custom launcher string is supplied, the compiler won't output ANY launcher / init code by itself,
+# and instead outputs whatever is specified here. (You can use \n here for newline and \ for line continuantions)
+custom_launcher =
+
 # TODO should the 64tass arguments be in here too perhaps? So that the "program" parameter that now selects 1 of a few fixed sets of arguments, can be removed?
 # TODO should an emulator command line also be in here perhaps? So that -emu will work too.