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494 lines
15 KiB
ArmAsm
494 lines
15 KiB
ArmAsm
;*****************************************************************************/
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;* */
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;* modload.s */
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;* */
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;* o65 module loader for the cc65 library */
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;* */
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;* */
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;* */
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;* (C) 2002 Ullrich von Bassewitz */
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;* Wacholderweg 14 */
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;* D-70597 Stuttgart */
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;* EMail: uz@musoftware.de */
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;* */
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;* */
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;* This software is provided 'as-is', without any expressed or implied */
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;* warranty. In no event will the authors be held liable for any damages */
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;* arising from the use of this software. */
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;* */
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;* Permission is granted to anyone to use this software for any purpose, */
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;* including commercial applications, and to alter it and redistribute it */
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;* freely, subject to the following restrictions: */
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;* */
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;* 1. The origin of this software must not be misrepresented; you must not */
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;* claim that you wrote the original software. If you use this software */
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;* in a product, an acknowledgment in the product documentation would be */
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;* appreciated but is not required. */
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;* 2. Altered source versions must be plainly marked as such, and must not */
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;* be misrepresented as being the original software. */
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;* 3. This notice may not be removed or altered from any source */
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;* distribution. */
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;* */
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;*****************************************************************************/
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.include "o65.inc"
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.include "modload.inc"
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.import pushax, pusha0, push0, push1, decax1
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.import _malloc, _free, _memset
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.import __ZP_START__ ; Linker generated
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.importzp sp, ptr1, tmp1, regbank
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.macpack generic
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;------------------------------------------------------------------------------
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; Variables stored in the register bank in the zero page. Placing the variables
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; here will protect them when calling other C functions.
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Module = regbank+0 ; Pointer to module memory
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Ctrl = regbank+2 ; Pointer to mod_ctrl structure
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TPtr = regbank+4 ; Pointer to module data for relocation
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;------------------------------------------------------------------------------
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; Static module data
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.bss
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; Save areas and error recovery data
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Stack: .byte 0 ; Old stackpointer
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RegBankSave: .res 6 ; Save area for register bank
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; The header of the o65 file. Since we don't need the first 8 bytes any
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; longer, once we've checked them, we will overlay them with other data to
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; save a few bytes.
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Header: .res O65_HDR_SIZE ; The o65 header
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; Input
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InputByte = Header ; Byte read from input
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; Segment addresses. Since the ld65 linker uses a relocation base address
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; of zero for all segments, the addresses of the segments are also the
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; relocation values.
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CodeAddr = Module ; Address of code seg
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DataAddr = Header + 1 ; Address of data seg
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BssAddr = Header + 3 ; Address of bss seg
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.data
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Read: jmp $FFFF ; Jump to read routine
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.rodata
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ExpectedHdr: .byte $01, $00 ; non C64 marker
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.byte $6F, $36, $35 ; Magic ("o65")
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.byte $00 ; Version
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.word $0000 ; Mode word
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ExpectedHdrSize = * - ExpectedHdr
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;------------------------------------------------------------------------------
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; PushCtrl: Push the address of the control structure onto the C stack.
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.code
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PushCtrl:
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lda Ctrl
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ldx Ctrl+1
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jmp pushax
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;------------------------------------------------------------------------------
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; RestoreRegBank: Restore the register bank contents from the save area. Will
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; destroy A and X (the latter will be zero on return).
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.code
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RestoreRegBank:
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ldx #6
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@L1: lda RegBankSave-1,x
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sta regbank-1,x
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dex
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bne @L1
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rts
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;------------------------------------------------------------------------------
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; GetReloc: Return a relocation value based on the segment in A
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.code
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GetReloc:
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cmp #O65_SEGID_TEXT
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bne @L1
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lda CodeAddr
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ldx CodeAddr+1
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rts
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@L1: cmp #O65_SEGID_DATA
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bne @L2
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lda DataAddr
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ldx DataAddr+1
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rts
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@L2: cmp #O65_SEGID_BSS
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bne @L3
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lda BssAddr
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ldx BssAddr+1
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rts
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@L3: cmp #O65_SEGID_ZP
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bne FormatError
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lda #<__ZP_START__
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ldx #>__ZP_START__
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rts
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;------------------------------------------------------------------------------
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; FormatError: Bail out with an o65 format error
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FormatError:
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lda #MLOAD_ERR_FMT
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; bne CleanupAndExit ; Branch always
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;------------------------------------------------------------------------------
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; CleanupAndExit: Free any allocated resources, restore the stack and return
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; to the caller.
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.code
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CleanupAndExit:
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; Restore the stack so we may return to the caller from here
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ldx Stack
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txs
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; Save the error return code
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pha
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; Check if we have to free the allocated block
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lda Module
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ora Module+1
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beq @L1 ; Jump if no memory allocated
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lda Module
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ldx Module+1
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jsr _free ; Free the allocated block
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; Restore the register bank
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@L1: jsr RestoreRegBank
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; Restore the error code and return to the caller
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ldx #$00 ; Load the high byte
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pla
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rts
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;------------------------------------------------------------------------------
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; ReadByte: Read one byte with error checking into InputByte and A.
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; ReadAndCheckError: Call read with the current C stack and check for errors.
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.code
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ReadByte:
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; C->read (C, &B, 1)
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jsr PushCtrl
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lda #<InputByte
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ldx #>InputByte
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jsr pushax
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jsr push1
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; This is a second entry point used by the other calls to Read
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ReadAndCheckError:
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jsr Read
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; Check the return code and bail out in case of problems
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tax
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beq @L1 ; Jump if ok
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lda #MLOAD_ERR_READ
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bne CleanupAndExit
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; Done
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@L1: lda InputByte ; If called ReadByte, load the byte read
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Done: rts
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;------------------------------------------------------------------------------
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; RelocSeg: Relocate the segment pointed to by a/x
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.code
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RelocSeg:
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jsr decax1 ; Start value is segment-1
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sta TPtr
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stx TPtr+1
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Loop: jsr ReadByte ; Read byte from relocation table
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beq Done ; Bail out if end of table reached
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cmp #255 ; Special offset?
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bne @L1
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; Increment offset by 254 and continue
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lda TPtr
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add #254
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sta TPtr
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bcc Loop
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inc TPtr+1
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jmp Loop
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; Increment offset by A
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@L1: add TPtr
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sta TPtr
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bcc @L2
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inc TPtr+1
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; Read the relocation byte, extract the segment id, fetch the corresponding
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; relocation value and place it into ptr1
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@L2: jsr ReadByte
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and #O65_SEGID_MASK
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jsr GetReloc
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sta ptr1
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stx ptr1+1
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; Get the relocation byte again, this time extract the relocation type.
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lda InputByte
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and #O65_RTYPE_MASK
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; Check for and handle the different relocation types.
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cmp #O65_RTYPE_WORD
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beq RelocWord
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cmp #O65_RTYPE_HIGH
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beq RelocHigh
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cmp #O65_RTYPE_LOW
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bne FormatError
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; Relocate the low byte
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RelocLow:
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ldy #0
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clc
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lda (TPtr),y
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adc ptr1
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sta (TPtr),y
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jmp Loop
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; Relocate a high byte
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RelocHigh:
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jsr ReadByte ; Read low byte from relocation table
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ldy #0
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clc
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adc ptr1 ; We just need the carry
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AddHigh:lda (TPtr),y
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adc ptr1+1
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sta (TPtr),y
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jmp Loop ; Done, next entry
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; Relocate a word
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RelocWord:
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ldy #0
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clc
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lda (TPtr),y
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adc ptr1
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sta (TPtr),y
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iny
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bne AddHigh ; Branch always (add high byte)
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;------------------------------------------------------------------------------
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; mod_load: Load and relocate an o65 module
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.code
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_mod_load:
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; Save the register bank and clear the Module pointer
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pha
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ldy #6
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@L1: lda regbank-1,y
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sta RegBankSave-1,y
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dey
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bne @L1
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sty Module
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sty Module+1
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pla
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; Save the passed parameter
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sta Ctrl
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stx Ctrl+1
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; Save the stack pointer so we can bail out even from subroutines
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tsx
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stx Stack
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; Get the read function pointer from the control structure and place it into
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; our call vector
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ldy #MODCTRL_READ
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lda (Ctrl),y
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sta Read+1
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iny
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lda (Ctrl),y
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sta Read+2
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; Read the o65 header: C->read (C, &H, sizeof (H))
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jsr PushCtrl
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lda #<Header
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ldx #>Header
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jsr pushax
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lda #O65_HDR_SIZE
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jsr pusha0 ; Always less than 256
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jsr ReadAndCheckError ; Bails out in case of errors
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; We read the o65 header successfully. Validate it.
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ldy #ExpectedHdrSize-1
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@L3: lda Header,y
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cmp ExpectedHdr,y
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beq @L4
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lda #MLOAD_ERR_HDR
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jmp CleanupAndExit
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@L4: dey
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bpl @L3
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; Header is ok as far as we can say now. Read and skip all options. We may
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; add a check here for the OS option later.
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Opt: jsr ReadByte
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beq OptDone ; Jump if done
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sta TPtr ; Use TPtr as a counter
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OneOpt: dec TPtr
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beq Opt ; Next option
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jsr ReadByte ; Skip one byte
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jmp OneOpt
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OptDone:
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; Skipped all options. Calculate the size of text+data and of text+data+bss
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; (the latter is the size of the memory block we need). We will store the
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; total module size also into the control structure for evaluation by the
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; caller
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lda Header + O65_HDR_TLEN
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add Header + O65_HDR_DLEN
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sta TPtr
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lda Header + O65_HDR_TLEN + 1
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adc Header + O65_HDR_DLEN + 1
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sta TPtr+1
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lda TPtr
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add Header + O65_HDR_BLEN
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pha ; Save low byte of total size
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ldy #MODCTRL_MODULE_SIZE
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sta (Ctrl),y
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lda TPtr+1
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adc Header + O65_HDR_BLEN + 1
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iny
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sta (Ctrl),y
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tax
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pla ; Restore low byte of total size
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; Total memory size is now in a/x. Allocate memory, check if we got it.
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jsr _malloc
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sta Module
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stx Module+1
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ora Module+1
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bne GotMem
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; Could not allocate memory
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lda #MLOAD_ERR_MEM
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jmp CleanupAndExit
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; We got the memory block. Place a pointer to the memory block also in the
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; module control structure.
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GotMem: lda Module ; Ctrl->module = Module;
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ldy #MODCTRL_MODULE
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sta (Ctrl),y
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txa
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iny
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sta (Ctrl),y
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; Calculate the start addresses of the segments. Since the linker uses a
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; base address of zero for all segments, the load addresses are also the
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; relocation values for the segments.
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lda Module
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add Header + O65_HDR_TLEN
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sta DataAddr
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lda Module + 1
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adc Header + O65_HDR_TLEN + 1
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sta DataAddr + 1
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lda Module
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add TPtr
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sta BssAddr
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lda Module+1
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add TPtr+1
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sta BssAddr + 1
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; Control structure is complete now. Load code and data segment into memory.
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; The sum of the sizes of code+data segment is still in TPtr.
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; C->read (C, C->module, H.tlen + H.dlen)
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jsr PushCtrl
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lda Module
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ldx Module+1
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jsr pushax
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lda TPtr
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ldx TPtr+1
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jsr pushax
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jsr ReadAndCheckError ; Bails out in case of errors
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; We've got the code and data segments in memory. Next section contains
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; undefined references which we don't support. So check if the count of
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; undefined references is actually zero.
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jsr ReadByte
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bne Undef
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jsr ReadByte
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beq Reloc
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Undef: jmp FormatError
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; Number of undefined references was zero. Next come the relocation tables
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; for code and data segment. Relocate the code segment
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Reloc: lda Module
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ldx Module + 1 ; Code segment address
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jsr RelocSeg
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; Relocate the data segment
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lda Module
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add Header + O65_HDR_TLEN
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pha
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lda Module + 1
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adc Header + O65_HDR_TLEN + 1
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tax
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pla ; Date segment address in a/x
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jsr RelocSeg
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; Clear the bss segment: memset (bss_addr, 0, bss_size)
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lda BssAddr
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ldx BssAddr + 1
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jsr pushax
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jsr push0
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lda Header + O65_HDR_BLEN
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ldx Header + O65_HDR_BLEN+1
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jsr _memset ; memset (bss, 0, bss_size);
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; We're done. Restore the register bank and return a success code
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jsr RestoreRegBank ; X will be zero on return
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lda #MLOAD_OK
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rts
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