Follow-up fix of linkscript after [1]. The linkscript
incorrectly relies on lazy evaluation to computes the
start of the .bss segment in RAM, leaving all linked
symbols incorrectly shifted in memory.
Re-work the backup RAM definition in the linkscript
with a proper MEMORY command, and expose macros in
the ngdevkit API to override the start and length of
the backup RAM at link-time.
After the linkscript update to support large P-ROMs [1,2],
the ordering of the bss and backup RAM segments has changed,
and this broke the logic used to compute the start of the .bss
segment in RAM. Fix accordingly.
After #78 and #81, the .bss segment is now linked prior to the
.data segment. The crt0 still assumes the opposite, so the
memory is incorrectly initialized.
Since the linker now exposes symbol __bss_start_in_ram, the crt0
no longer needs to assume any ordering. Fix it accordingly.
New API to map a specific chunk of the the second P-ROM into the
P-ROM2 memory address space at runtime (0x200000..0x2fffff).
To support bank-switching transparently, the order in which the
ELF sections are linked is modified: the devkit's code is always
linked in the first P-ROM, as well as all data. The user code
gets linked last, and all files whose path contain the substring
`__bank` get implicitly linked in the second P-ROM.
This changes the way the program ROM are linked. The
BRAM, BSS and RAM segments go first, the code itself being
linked at the very end of the P-ROM adress space.
The linker now allows the full 1MiB address space for
large P-ROM, as well as 2MiB non-contiguous P-ROM (2x1MiB).
This is a breaking change, the .text sections in the output
ELF file are no longer padded automatically. You now need to
add the proper padding when extracting code with objcopy.
dciabrin/ngdevkit-examples@03c250a0ee55bb05501a79ebb4c9401217d9959d
has been updated to implement padding appropriately.
A new section in ngdevkit linkscript and an associated
C macro allows variables to be stored in a location that
gets automatically saved to backup RAM on MVS.
