mirror of
https://github.com/cc65/cc65.git
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0ee9b2e446
So far the INIT segment was run from the later heap+stack. Now the INIT segment is run from the later BSS. The background is that so far the INIT segment was pretty small (from $80 to $180 bytes). But upcoming changes will increase the INIT segment in certain scenarios up to ~ $1000 bytes. So programs with very limited heap+stack might just not been able to move the INIT segment to its run location. But moving the INIT segment to the later BSS allows it to occupy the later BSS+heap+stack. In order to allow that the constructors are _NOT_ allowed anymore to access the BSS. Rather they must use the DATA segment or the new INITBSS segment. The latter isn't cleared at any point so the constructors may use it to expose values to the main program. However they must make sure to always write the values as they are not pre-initialized.
140 lines
3.2 KiB
ArmAsm
140 lines
3.2 KiB
ArmAsm
;
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; Startup code for cc65 (C64 version)
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;
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.export _exit
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.export __STARTUP__ : absolute = 1 ; Mark as startup
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.import initlib, donelib
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.import moveinit, zerobss, callmain
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.import BSOUT
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.import __MAIN_START__, __MAIN_SIZE__ ; Linker generated
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.import __STACKSIZE__ ; from configure file
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.importzp ST
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.include "zeropage.inc"
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.include "c64.inc"
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; ------------------------------------------------------------------------
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; Startup code
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.segment "STARTUP"
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Start:
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; Switch to the second charset.
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lda #14
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jsr BSOUT
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; Switch off the BASIC ROM.
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lda $01
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sta mmusave ; Save the memory configuration
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and #$F8
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ora #$06 ; Enable Kernal+I/O, disable BASIC
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sta $01
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tsx
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stx spsave ; Save the system stack ptr
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; Allow some re-entrancy by skipping the next task if it already was done.
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; This sometimes can let us rerun the program without reloading it.
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ldx move_init
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beq L0
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; Move the INIT segment from where it was loaded (over the bss segments)
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; into where it must be run (over the BSS segment).
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jsr moveinit
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dec move_init ; Set to false
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; Save space by putting some of the start-up code in the INIT segment,
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; which can be re-used by the BSS segment, the heap and the C stack.
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L0: jsr runinit
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; Clear the BSS data.
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jsr zerobss
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; Push the command-line arguments; and, call main().
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jsr callmain
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; Back from main() [this is also the exit() entry]. Run the module destructors.
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_exit: pha ; Save the return code on stack
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jsr donelib
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; Copy back the zero-page stuff.
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ldx #zpspace-1
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L2: lda zpsave,x
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sta sp,x
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dex
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bpl L2
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; Place the program return code into BASIC's status variable.
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pla
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sta ST
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; Restore the system stuff.
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ldx spsave
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txs ; Restore stack pointer
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ldx mmusave
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stx $01 ; Restore memory configuration
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; Back to BASIC.
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rts
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; ------------------------------------------------------------------------
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.segment "INIT"
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runinit:
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; Save the zero-page locations that we need.
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ldx #zpspace-1
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L1: lda sp,x
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sta zpsave,x
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dex
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bpl L1
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; Set up the stack.
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lda #<(__MAIN_START__ + __MAIN_SIZE__ + __STACKSIZE__)
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ldx #>(__MAIN_START__ + __MAIN_SIZE__ + __STACKSIZE__)
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sta sp
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stx sp+1 ; Set argument stack ptr
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; Call the module constructors.
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jmp initlib
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; ------------------------------------------------------------------------
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; Data
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.data
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; These two variables were moved out of the BSS segment, and into DATA, because
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; we need to use them before INIT is moved off of BSS, and before BSS is zeroed.
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mmusave:.res 1
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spsave: .res 1
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move_init:
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.byte 1
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.segment "INITBSS"
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zpsave: .res zpspace
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