Port atari open and close from cc65

mos-platform/atari8-common/CMakeLists.txt

@@ -28,5 +28,14 @@ target_link_libraries(atari8-common-crt0 PRIVATE common-asminc)
 add_platform_library(atari8-common-c
   putchar.c
   getchar.c
+
+  close.s
+  fdtab.s
+  fdtable.s
+  findfreeiocb.s
+  getfd.s
+  open.s
+  oserror.s
 )
-target_include_directories(atari8-common-c SYSTEM BEFORE PUBLIC .)
+target_include_directories(atari8-common-c BEFORE PUBLIC .)
+target_link_libraries(atari8-common-c PRIVATE common-asminc)

mos-platform/atari8-common/close.s

@@ -0,0 +1,38 @@
+; Copyright 2024 LLVM-MOS Project
+; Licensed under the Apache License, Version 2.0 with LLVM Exceptions.
+; See https://github.com/llvm-mos/llvm-mos-sdk/blob/main/LICENSE for license
+; information.
+
+; Originally from cc65. Modified from original version.
+
+;
+; Christian Groessler, May-2000
+;
+; int __fastcall__ close(int fd);
+;
+
+        .include "atari.inc"
+        .include "errno.inc"
+
+        .globl  close
+
+close:
+        jsr     fdtoiocb_down           ; get iocb index into X and decr. usage count
+        bmi     inverr
+        bne     ok                      ; not last one -> don't close yet
+        lda     #CLOSE
+        sta     ICCOM,x
+        jsr     CIOV
+        bmi     closerr
+ok:     ldx     #0
+        stx     __oserror               ; clear system specific error code
+        txa
+        rts
+
+inverr: lda     #<EINVAL
+        jmp     __directerrno
+
+closerr:
+        tya
+        jmp     __mappederrno
+

mos-platform/atari8-common/fd.inc

@@ -0,0 +1,27 @@
+; Copyright 2024 LLVM-MOS Project
+; Licensed under the Apache License, Version 2.0 with LLVM Exceptions.
+; See https://github.com/llvm-mos/llvm-mos-sdk/blob/main/LICENSE for license
+; information.
+
+; Originally from cc65. Modified from original version.
+
+; Christian Groessler, Oct-2000
+;
+; offsets and defines for fdtable (internal use only)
+;
+
+MAX_FD_INDEX    =       12      ; max. # of open fds
+MAX_FD_VAL      =       8       ; we have 8 IOCBs
+
+ft_entrylen = 4 ; length of table entry (it's not sufficient to change here!
+                ; the code sometimes does two bit shifts to multiply/divide by
+                ; this length)
+
+ft_usa  = 0     ; usage counter
+ft_iocb = 1     ; iocb index (0,$10,$20,etc.), $ff for empty entry
+ft_dev  = 2     ; device of open iocb (0 - device not remembered, eg. filename specified)
+ft_flag = 3     ; flags
+                ; lower 3 bits: device number (for R: and D:)
+                ; bit 3 - seeking supported by DOS/disk combination
+                ; bit 4 - indicates a fd opened by the program as apposed to the
+                ;         inherited ones from program start (fd 0 to fd 2)

mos-platform/atari8-common/fdtab.s

@@ -0,0 +1,34 @@
+; Copyright 2024 LLVM-MOS Project
+; Licensed under the Apache License, Version 2.0 with LLVM Exceptions.
+; See https://github.com/llvm-mos/llvm-mos-sdk/blob/main/LICENSE for license
+; information.
+
+; Originally from cc65. Modified from original version.
+
+;
+; Christian Groessler, Oct-2000
+; Daniel Serpell, Dec-2009
+;
+; the fdtable itself is defined here
+;
+
+        .include "fd.inc"
+
+        .globl fd_table,fd_index
+
+        .data
+
+fd_index:       ; fd number is index into this table, entry's value specifies the fd_table entry
+        .byte   0,0,0           ; at start, three first files are stdin/stdout/stderr.
+        .space  MAX_FD_INDEX-3,$ff
+
+fd_table:       ; each entry represents an open iocb
+        .byte   3,0,'E',0       ; system console, app starts with opened iocb #0 for E:
+        .byte   0,$ff,0,0
+        .byte   0,$ff,0,0
+        .byte   0,$ff,0,0
+        .byte   0,$ff,0,0
+        .byte   0,$ff,0,0
+        .byte   0,$ff,0,0
+        .byte   0,$ff,0,0
+