Possible linker optimisations

[colinleroy]

Hi,
I'm currently on a project where the executables are big, due to my use of video, which reserves $2000-$3FFF for video). There is also too much code to use --start-addr 0x4000, so my binary looks like this, with code split below and above HGR video memory:

NULL                  000000  000000  000000  00001
ZEROPAGE              000080  000099  00001A  00001
EXEHDR                0007C9  000802  00003A  00001
STARTUP               000803  000839  000037  00001
LOWCODE               00083A  001FDA  0017A1  00001
HGR                   002000  003FFF  002000  00001
CODE                  004000  00867F  004680  00100
RODATA                008680  008F2D  0008AE  00001
DATA                  008F2E  009118  0001EB  00001
INIT                  009119  009177  00005F  00001
RT_ONCE               009178  009C9C  000B25  00001
BSS                   009C9D  009FFD  000361  00001
ONCE                  009C9D  009E0A  00016E  00001
LC                    00D400  00DFAC  000BAD  00001

In this example, I have a problem where I would like to reserve the second graphics page ($4000-$5FFF) to be able to do double-buffering. But this doesn't work, because there is too much code:

ld65: Warning: ../../config/apple2enh-avstreamer.cfg:34: Segment 'BSS' with type 'bss' contains initialized data
ld65: Warning: ../../config/apple2enh-avstreamer.cfg:17: Segment 'LC' overflows memory area 'MAIN' by 2866 bytes
ld65: Error: ../../config/apple2enh-avstreamer.cfg:18: Size of memory area 'BSS' is negative: -535

It would be nice to be able to build a tighter binary. This could be done by storing the ONCE segment somewhere inside $2000-5FFF. The LC segment, which is an Apple2enh target thing, also stores code at the end of the binary, after ONCE, and relocates it to $D400 at startup.

Having the ability to store ONCE and LC at $4000 would allow my executable to build and run fine.
I have tried to move ONCE and LC in the linker config file, but there are assumptions both at build and runtime that ONCE is at the end of the binary.