.import pushax, pusha0, push0, push1, decax1
.import _malloc, _free, _memset
+ .import __ZP_START__ ; Linker generated
.importzp sp, ptr1, tmp1, regbank
.macpack generic
Stack: .byte 0 ; Old stackpointer
RegBankSave: .res 6 ; Save area for register bank
-; The header of the o65 file. Since we don't need the 8 bytes any longer,
-; once we've checked them, we will overlay them with other data to save a
-; few bytes.
+; The header of the o65 file. Since we don't need the first 8 bytes any
+; longer, once we've checked them, we will overlay them with other data to
+; save a few bytes.
Header: .res O65_HDR_SIZE ; The o65 header
; Input
InputByte = Header ; Byte read from input
-; Stuff needed for relocation
-TextReloc = Header + 1 ; Relocation value for code seg
-DataReloc = Header + 3 ; Relocation value for data seg
-BssReloc = Header + 5 ; Relocation value for bss seg
+; Stuff needed for relocation. Since the ld65 linker uses a relocation base
+; address of zero for all segments, the relocation values needed are actually
+; the start addresses of the segments. Among other things this means that the
+; relocation value for the text segment is the same as the start address as
+; the whole module block.
+TextReloc = Module ; Relocation value for code seg
+DataReloc = Header + 1 ; Relocation value for data seg
+BssReloc = Header + 3 ; Relocation value for bss seg
.data
Read: jmp $FFFF ; Jump to read routine
;------------------------------------------------------------------------------
; RestoreRegBank: Restore the register bank contents from the save area. Will
-; destroy A and X
+; destroy A and X (the latter will be zero on return).
.code
RestoreRegBank:
- ldx #6-1
-@L1: lda RegBankSave,x
- sta regbank,x
+ ldx #6
+@L1: lda RegBankSave-1,x
+ sta regbank-1,x
dex
- bpl @L1
+ bne @L1
rts
;------------------------------------------------------------------------------
ldx BssReloc+1
rts
-@L3: lda #MLOAD_ERR_FMT
+@L3: cmp #O65_SEGID_ZP
+ bne FormatError
+ lda #<__ZP_START__
+ ldx #>__ZP_START__
+ rts
+
+;------------------------------------------------------------------------------
+; FormatError: Bail out with an o65 format error
+
+FormatError:
+ lda #MLOAD_ERR_FMT
; bne CleanupAndExit ; Branch always
;------------------------------------------------------------------------------
;------------------------------------------------------------------------------
; ReadByte: Read one byte with error checking into InputByte and A.
+; ReadAndCheckError: Call read with the current C stack and check for errors.
.code
ReadByte:
ldx #>InputByte
jsr pushax
jsr push1
+
+; This is a second entry point used by the other calls to Read
+
+ReadAndCheckError:
jsr Read
; Check the return code and bail out in case of problems
; Done
-@L1: lda InputByte
+@L1: lda InputByte ; If called ReadByte, load the byte read
Done: rts
;------------------------------------------------------------------------------
; Check for and handle the different relocation types.
cmp #O65_RTYPE_WORD
- bne @L3
+ beq RelocWord
+ cmp #O65_RTYPE_HIGH
+ beq RelocHigh
+ cmp #O65_RTYPE_LOW
+ bne FormatError
+
+; Relocate the low byte
+
+RelocLow:
ldy #0
clc
lda (TPtr),y
adc ptr1
sta (TPtr),y
- iny
- bne @L4 ; Branch always (add high byte)
+ jmp Loop
-@L3: cmp #O65_RTYPE_HIGH
- bne @L5
+; Relocate a high byte
+
+RelocHigh:
jsr ReadByte ; Read low byte from relocation table
ldy #0
clc
adc ptr1 ; We just need the carry
-@L4: lda (TPtr),y
+AddHigh:lda (TPtr),y
adc ptr1+1
sta (TPtr),y
jmp Loop ; Done, next entry
-@L5: cmp #O65_RTYPE_LOW
- beq @L6
-
-; Problem: Invalid relocation code
+; Relocate a word
- lda #MLOAD_ERR_FMT
- jmp CleanupAndExit
-
-@L6: ldy #0
+RelocWord:
+ ldy #0
clc
lda (TPtr),y
adc ptr1
sta (TPtr),y
-
-; Finished with this relocation
-
- jmp Loop
+ iny
+ bne AddHigh ; Branch always (add high byte)
;------------------------------------------------------------------------------
; mod_load: Load and relocate an o65 module
jsr pushax
lda #O65_HDR_SIZE
jsr pusha0 ; Always less than 256
- jsr Read
-
-; Check the return code
-
- tax
- beq @L2
- lda #MLOAD_ERR_READ
- jmp CleanupAndExit
+ jsr ReadAndCheckError ; Bails out in case of errors
; We read the o65 header successfully. Validate it.
-@L2: ldy #ExpectedHdrSize-1
+ ldy #ExpectedHdrSize-1
@L3: lda Header,y
cmp ExpectedHdr,y
beq @L4
jmp OneOpt
OptDone:
-; Skipped all options. Calculate the sizes of several areas needed later
+; Skipped all options. Calculate the size of text+data and of text+data+bss
+; (the latter is the size of the memory block we need). We will store the
+; total module size also into the control structure for evaluation by the
+; caller
lda Header + O65_HDR_TLEN
add Header + O65_HDR_DLEN
sta TPtr+1
lda TPtr
add Header + O65_HDR_BLEN
- sta tmp1
+ pha ; Save low byte of total size
+ ldy #MODCTRL_MODULE_SIZE
+ sta (Ctrl),y
lda TPtr+1
adc Header + O65_HDR_BLEN + 1
-
-; Load the total module size into a/x and store it into the control structure
-
- ldy #MODCTRL_MODULE_SIZE + 1
+ iny
sta (Ctrl),y
tax
- dey
- lda tmp1
- sta (Ctrl),y
+ pla ; Restore low byte of total size
-; Allocate memory, check if we got it
+; Total memory size is now in a/x. Allocate memory, check if we got it.
jsr _malloc
sta Module
; structure. We will use internal knowlege about the layout of the structure
; here to save some code.
-GotMem: lda Module
+GotMem: lda Module ; Ctrl->module = Module;
ldy #MODCTRL_MODULE
sta (Ctrl),y
- ldy #MODCTRL_CODE
+ ldy #MODCTRL_CODE ; Ctrl->code = Module;
sta (Ctrl),y
txa
iny
cpy #MODCTRL_SIZE
bne CLoop
-; Missing in the control structure now: start of the data and bss segments
+; Missing in the control structure now: start of the data and bss segments.
+; Since the linker relocates all segments to zero, these addresses are also
+; the relocation values for the segments.
ldy #MODCTRL_DATA
lda Module
add Header + O65_HDR_TLEN
sta (Ctrl),y
+ sta DataReloc
iny
lda Module + 1
adc Header + O65_HDR_TLEN + 1
sta (Ctrl),y
+ sta DataReloc + 1
ldy #MODCTRL_BSS
lda Module
add TPtr
sta (Ctrl),y
+ sta BssReloc
iny
lda Module+1
add TPtr+1
sta (Ctrl),y
+ sta BssReloc + 1
; Control structure is complete now. Load code and data segment into memory.
-; The sum of the sizes of code and data segment is still in TPtr.
+; The sum of the sizes of code+data segment is still in TPtr.
; C->read (C, C->module, H.tlen + H.dlen)
jsr PushCtrl
lda TPtr
ldx TPtr+1
jsr pushax
- jsr Read
-
-; Check for errors
-
- tax
- beq LoadOk
- lda #MLOAD_ERR_READ
- jmp CleanupAndExit
+ jsr ReadAndCheckError ; Bails out in case of errors
; We've got the code and data segments in memory. Next section contains
; undefined references which we don't support. So check if the count of
; undefined references is actually zero.
-LoadOk: jsr ReadByte
+ jsr ReadByte
bne Undef
jsr ReadByte
beq Reloc
-Undef: lda #MLOAD_ERR_FMT
- jmp CleanupAndExit
+Undef: jmp FormatError
; Number of undefined references was zero. Next sections are the relocation
-; tables for code and data segment. Before doing the actual relocation, we
-; have to setup the relocation values for the three segments.
+; tables for code and data segment. Relocate the code segment
Reloc: lda Module
- sub Header + O65_HDR_TBASE
- sta TextReloc
- lda Module + 1
- sbc Header + O65_HDR_TBASE + 1
- sta TextReloc + 1
-
- ldy #MODCTRL_DATA
- lda (Ctrl),y
- sub Header + O65_HDR_DBASE
- sta DataReloc
- iny
- lda (Ctrl),y
- sbc Header + O65_HDR_DBASE + 1
- sta DataReloc + 1
-
- ldy #MODCTRL_BSS
- lda (Ctrl),y
- sub Header + O65_HDR_BBASE
- sta BssReloc
- iny
- lda (Ctrl),y
- sbc Header + O65_HDR_BBASE + 1
- sta BssReloc + 1
-
-; Relocate the code segment
-
- lda Module
- ldx Module + 1 ; Code segment address
+ ldx Module + 1 ; Code segment address
jsr RelocSeg
; Relocate the data segment
ldy #MODCTRL_DATA + 1
- jsr LoadCtrl ; Get data segment address
+ jsr LoadCtrl ; Get data segment address
jsr RelocSeg
; Clear the bss segment
ldy #MODCTRL_BSS + 1
- jsr LoadCtrl ; Load bss segment address
+ jsr LoadCtrl ; Load bss segment address
jsr pushax
jsr push0
- ldy #MODCTRL_BSS_SIZE + 1
- jsr LoadCtrl ; Load bss segment size
- jsr _memset ; memset (bss, 0, bss_size);
+ lda Header + O65_HDR_BLEN
+ ldx Header + O65_HDR_BLEN+1
+ jsr _memset ; memset (bss, 0, bss_size);
; We're done. Restore the register bank and return a success code
- jsr RestoreRegBank
+ jsr RestoreRegBank ; X will be zero on return
lda #MLOAD_OK
rts
projects / cc65 / commitdiff