…ated, by default.

…nt-before/after can be parsed correctly.

Signed-off-by: Paul Osmialowski <[email protected]>

Signed-off-by: Paul Osmialowski <[email protected]>

Some caveat:

- The Z80 backend emits a lot of compiler library calls as specified in
  llvm/lib/Target/Z80/Z80ISelLowering.cpp making it slightly harder for
  practical use

The story:

Following the ability of the other 8-bit platform supported by LLVM (AVR) to
generate ELF object files, I have prepared this crude ELF code emitter
for Z80. It was not extensively tested, mostly due to the lack of a compatible
runtime library (e.g. for CP/M system). Yet for the testing purposes, I have
prepared something rudimentary, some minimalistic mockup of CP/M's libc allowing
me to prepare a simple executable .COM file. It consists of the following files:

1. _bdos.s

  .text

  .globl __csave
__csave:
  pop   hl      ; get the return address
  push  iy      ; preserve iy
  push  ix      ; preserve ix
  ld    ix, 0
  add   ix, sp  ; new frame pointer
  jp    (hl)    ; jump to return address

  .globl __crestore
__crestore:
  ld    sp, ix
  pop   ix      ; restore ix
  pop   iy      ; restore iy
  ret

; uint16_t _bdos(uint8_t function, uint16_t arg)
  .globl __bdos
__bdos:
  call  __csave
  ld    c, (ix + 6) ; ix + 6: function
  ld    e, (ix + 8) ; ix + 8: arg (LO)
  ld    d, (ix + 9) ; ix + 9: arg (HI)
  push  iy      ; preserve iy
  push  ix      ; preserve ix
  call  0x05    ; call BDOS
  pop   ix      ; restore ix
  pop   iy      ; restore iy
  ld    l, a    ; return the result in l
  rla           ; get the highest bit to the carry flag
  sbc   a, a    ; keep the carry flag
  ld    h, a    ; return the highest bit in h
  jp    __crestore

Compile this with the GNU 'as' from binutils built with --target=z80-none-elf
'configure' flag, e.g.:

z80-none-elf-as -o _bdos.o _bdos.s

2. _exit.s

  .text
  .globl __Exit
__Exit:
  pop hl        ; get rid of the return address
  pop hl        ; exit status
  ld (0x80), hl ; store exit status at the address 0x80
  jp 0          ; return to CP/M

Similarly:

z80-none-elf-as -o _exit.o _exit.s

3. crtcpm.c

_Noreturn void _Exit(int);

int main(int, char **);

_Noreturn void start(void) __attribute__((no_builtin))
{
  // TODO: parse whatever there is at 0x80
  static char *argv[] =  { (char *)(0x80) };

  _Exit(main(1, argv));
}

Compile this (to 'crtcpm.o') with the LLVM compiler built with
-DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD="Z80", -DLLVM_TARGETS_TO_BUILD="" and
-DLLVM_DEFAULT_TARGET_TRIPLE="z80-none-elf" 'cmake' flags, namely:

clang -Wall -O0 -fintegrated-as -fomit-frame-pointer -c crtcpm.c

4. main.c

uint16_t _bdos(uint8_t, uint16_t);

static void putch(int c)
{
  if ('\n' == c)
    _bdos(0x02U, '\r');
  _bdos(0x02U, c);
}

int main(int argc, char **argv)
{
  int i;
  int c;
  const int n = ((unsigned char)(argv[0][0]));

  for (i = 0; i < n; i++) {
    c = ((unsigned char)(argv[0][1 + i]));
    putch('[');
    if (' ' == c) {
      putch('s');
      putch('p');
    } else
      putch(c);
    putch(']');
  }
  putch('\n');
  return argc;
}

Similarly, build 'main.o':

clang -Wall -fintegrated-as -c main.c

Create rudimentary 'libc.a' library from '_bdos.o' and '_exit.o' using GNU 'ar'
and 'runlib' from binutils built as described earlier:

z80-none-elf-ar r libc.a _bdos.o _exit.o
z80-none-elf-ranlib libc.a

Link the final .COM file, e.g.:

z80-none-elf-ld -o main.com --oformat binary -Ttext=0x100 crtcpm.o main.o -L. -lc

Every CP/M program should start at 0x100, hence the .text segment is set to
start at that address. The .data segment will be placed right after last byte of
the .text segment. Note that 'crtcpm.o' is kept separately from 'libc.a' and is
listed as the very first file needed to link the final program. This ensures
that the only function defined in 'crtcpm.o' (the _start() function) will be the
very first thing placed at the address 0x100.

Copy the 'main.com' file to a disk image and execute it in CP/M. Basically,
the 'main.com' program should print whatever was given as parameters with each
character put into brackets (and spaces printed as [sp]):

A>main hello, world
[sp][H][E][L][L][O][,][sp][W][O][R][L][D]

Note that CP/M turns all the characters in the command line arguments
into upper-case.

Signed-off-by: Paul Osmialowski <[email protected]>