6502: Usermode execution start up code

diff --git a/Library/libs/crt0_6502.s b/Library/libs/crt0_6502.s
new file mode 100644 (file)
index 0000000..94db7cc
--- /dev/null
+++ b/Library/libs/crt0_6502.s
@@ -0,0 +1,72 @@
+;
+; Startup code for cc65 on FUZIX
+;
+; Based on code by Debrune Jérôme <jede@oric.org>
+; and Ullrich von Bassewitz <uz@cc65.org> 2014-08-22, Greg King
+;
+
+        .export         _exit
+        .import         initlib, donelib
+       .import         __CODE_SIZE__, __RODATA_SIZE__
+       .import         __DATA_SIZE__, __BSS_SIZE__
+       .import         __exit
+       .import         _environ
+
+        .include        "zeropage.inc"
+
+; Place the startup code in a special segment.
+
+.segment        "STARTUP"
+       jmp     start
+
+       .byte   'F'
+       .byte   'Z'
+       .byte   'X'
+       .byte   '1'
+       .byte   $20
+       .word   0
+       .word   __CODE_SIZE__ + __RODATA_SIZE__
+       .word   __DATA_SIZE__
+       .word   __BSS_SIZE__
+       .word   0
+
+;
+;      On entry sp/sp+1 have been set up by the kernel (this has to be
+;      done in kernel as we might take a signal very early on). Above the
+;      sp are the argument vectors, environment etc. In other words we
+;      are basically a straight function call from the kernel stub.
+;
+;      Our image has been loaded into RAM, any spare memory has been zeroed
+;      for us and we are ready to roll.
+;
+start:
+; Call the module constructors.
+        jsr     initlib
+
+; Push the command-line arguments; and, call main().
+;
+; Need to save the environment ptr. The rest of the stack should be
+; fine.
+;
+       lda     _sp
+       ldx     _sp+1
+       clc
+       adc     #4
+       bcc     l1
+       inx
+l1:    sta     _environ
+       stx     _environ+1
+       ldy     #4
+        jsr     callmain
+
+; Call the module destructors. This is also the exit() entry.
+
+_exit:  pha
+       txa
+       pha
+       jsr     donelib         ; Run module destructors
+       pla
+       tax
+       pla
+       jmp     __exit          ; exit syscall, AX holds our return code
+                               ; for a fastcall return to nowhere.
\ No newline at end of file