#3109 SDLDGB has fixed base address for _CODE area

[Tony Pavlov]

there is an order of areas defined in crt0.s:

    ;; Ordering of segments for the linker
    ;; Code that really needs to be in bank 0
    .area    _HOME
    ;; Similar to _HOME
    .area    _BASE
    ;; Code
    .area    _CODE
    ;; Constant data
    .area    _LIT
    ;; Constant data used to init _DATA
    .area    _GSINIT
    .area    _GSINITTAIL
    .area    _GSFINAL
    ;; Initialised in ram data
    .area    _DATA
    ;; Uninitialised ram data
    .area    _BSS
    ;; For malloc
    .area    _HEAP

    .area    _BSS

if you don't pass base address of _CODE into the linker - that result into broken rom, because it's base address assigned to 0 and header gets overwritten.

but when you set base address of _CODE with linker commandline to 0x0200, that produces valid ROM, but results in inserting _CODE section before _HOME and _BASE. that is wrong, because _HOME contains ISRs, trampolines for banked calls, etc, and, depending on the size of the _CODE, that might result into pushing critical code out of bank 0. base address of _CODE should be calculated the same way as _BASE and _HOME. (actually, assigning _CODE base address in the linker should be simply removed).

[Tony Pavlov]

ps: SDCC itself, when calling the linker also passes base address for _CODE in SDCCmain.c:

          WRITE_SEG_LOC ("_CODE", options.code_loc);

and in z80/main.c:

  options.code_loc = 0x200;

it should not do that.