From 4335d248d18987a050d8ac26965c90718eef7562 Mon Sep 17 00:00:00 2001
From: user <user@clank>
Date: Thu, 16 Jul 2026 07:21:40 +0200
Subject: libc + CLI tools: a small C userland

- libc: add putc, puts, strlen, getargs (args string), EOF (=4) for readc.
- args: shell splits the command line at the first space ("cmd\0args\0" at
  $A000, inherited by the child via fork); getargs() returns the arg string.
- shell: exit on Ctrl-D/EOF; $ prompt over a clean read loop.
- tools (c/): echo (argv), cat (stdin->stdout to EOF), uname, pid (decimal
  print), true, false. Each built to a ROM-bank blob and registered.
- Makefile: CBLOBS list builds all C programs.
- README: document libc + the tool set.
---
 c/cat.c   | 10 ++++++++
 c/crt0.s  |  6 ++---
 c/echo.c  |  5 ++++
 c/false.c |  2 ++
 c/gbos.h  | 16 ++++++++----
 c/libc.s  | 84 +++++++++++++++++++++++++++++++++++++++++++--------------------
 c/pid.c   |  9 +++++++
 c/true.c  |  2 ++
 c/uname.c |  2 ++
 9 files changed, 102 insertions(+), 34 deletions(-)
 create mode 100644 c/cat.c
 create mode 100644 c/echo.c
 create mode 100644 c/false.c
 create mode 100644 c/pid.c
 create mode 100644 c/true.c
 create mode 100644 c/uname.c

(limited to 'c')

diff --git a/c/cat.c b/c/cat.c
new file mode 100644
index 0000000..4092778
--- /dev/null
+++ b/c/cat.c
@@ -0,0 +1,10 @@
+#include "gbos.h"
+/* cat: copy stdin to stdout until EOF (Ctrl-D / pipe end). */
+void main(void) {
+    char c;
+    for (;;) {
+        c = readc();
+        if (c == EOF) break;
+        putc(c);
+    }
+}
diff --git a/c/crt0.s b/c/crt0.s
index cde4b67..0d8371f 100644
--- a/c/crt0.s
+++ b/c/crt0.s
@@ -1,11 +1,11 @@
 	.module crt0
 	.globl _main
-	;; gbos C entry. exec() maps our ROM bank and jumps to the start of _CODE
-	;; (linked at 0x4000). Call main(), then exit(0). exec() already set SP.
+	;; gbos C entry. exec() maps our ROM bank and jumps here ($4000).
+	;; Call main(), then exit(0). (Args are fetched on demand via getargs().)
 	.area _CODE
 _start::
 	call	_main
 	ld	b, #0
-	ld	c, #0		; SYS_EXIT
+	ld	c, #0			; SYS_EXIT
 	rst	#0x30
 1$:	jr	1$
diff --git a/c/echo.c b/c/echo.c
new file mode 100644
index 0000000..f8d5125
--- /dev/null
+++ b/c/echo.c
@@ -0,0 +1,5 @@
+#include "gbos.h"
+void main(void) {
+    puts(getargs());
+    nl();
+}
diff --git a/c/false.c b/c/false.c
new file mode 100644
index 0000000..a124951
--- /dev/null
+++ b/c/false.c
@@ -0,0 +1,2 @@
+#include "gbos.h"
+void main(void) { sexit(1); }
diff --git a/c/gbos.h b/c/gbos.h
index 9a09a5d..3a10e06 100644
--- a/c/gbos.h
+++ b/c/gbos.h
@@ -1,9 +1,15 @@
-/* gbos userland C API (thin wrappers over rst $30 syscalls; see c/libc.asm) */
+/* gbos userland C API (thin wrappers over rst $30 syscalls; see c/libc.s) */
 #ifndef GBOS_H
 #define GBOS_H
-void          writes(const char *buf, unsigned char len); /* write to console */
-void          nl(void);                                   /* newline (CRLF)   */
-unsigned char readc(void);                                /* read one byte    */
-void          sexit(unsigned char code);                  /* exit(code)       */
+#define EOF 4                 /* readc() returns this at end of input */
+
+void          writes(const char *buf, unsigned char len);
+void          putc(char c);
+void          puts(const char *s);        /* write a NUL-terminated string */
+void          nl(void);                   /* newline (CRLF)                */
+unsigned char strlen(const char *s);
+char         *getargs(void);              /* this program's argument string */
+char          readc(void);                /* one input byte, EOF at end    */
+void          sexit(unsigned char code);
 unsigned char getpid(void);
 #endif
diff --git a/c/libc.s b/c/libc.s
index 4fca5e3..29031e9 100644
--- a/c/libc.s
+++ b/c/libc.s
@@ -1,19 +1,48 @@
 	.module libc
-	.globl _writes, _nl, _readc, _sexit, _getpid
+	.globl _writes, _putc, _puts, _nl, _strlen, _readc, _sexit, _getpid, _getargs
+	;; SDCC sm83 sdcccall(1): 1st arg -> A (byte) or DE (pointer); ret A / BC.
+	;; rst $30 (the trap) clobbers BC/DE/HL; SDCC treats them caller-saved, so
+	;; wrappers need not preserve them - but we compute cleanly regardless.
 	.area _CODE
+
 	;; void writes(const char *buf /*DE*/, unsigned char len /*A*/)
 _writes:
-	push	hl
-	push	de
-	push	bc
 	ld	b, a
-	ld	c, #3		; SYS_WRITE
+	ld	c, #3			; SYS_WRITE
 	rst	#0x30
-	pop	bc
-	pop	de
-	pop	hl
 	ret
-	;; void nl(void) - CRLF straight to serial
+
+	;; char *getargs(void) -> BC : the arg string (command line past word 1).
+	;; The shell leaves "cmd\0args\0" at 0xA000, inherited by the child via fork.
+_getargs:
+	ld	hl, #0xa000
+1$:	ld	a, (hl)
+	inc	hl
+	or	a
+	jr	nz, 1$
+	ld	b, h
+	ld	c, l
+	ret
+
+	;; void putc(char c /*A*/)
+_putc:
+	ld	(0xff01), a
+	ld	a, #0x81
+	ld	(0xff02), a
+	ret
+
+	;; void puts(const char *s /*DE*/) - write until NUL (no newline)
+_puts:
+1$:	ld	a, (de)
+	or	a
+	ret	z
+	ld	(0xff01), a
+	ld	a, #0x81
+	ld	(0xff02), a
+	inc	de
+	jr	1$
+
+	;; void nl(void) - CRLF
 _nl:
 	ld	a, #0x0d
 	ld	(0xff01), a
@@ -24,31 +53,34 @@ _nl:
 	ld	a, #0x81
 	ld	(0xff02), a
 	ret
-	;; unsigned char readc(void) -> A
+
+	;; unsigned char strlen(const char *s /*DE*/) -> A
+_strlen:
+	ld	c, #0
+1$:	ld	a, (de)
+	or	a
+	jr	z, 2$
+	inc	c
+	inc	de
+	jr	1$
+2$:	ld	a, c
+	ret
+
+	;; char readc(void) -> A   (4 = EOF)
 _readc:
-	push	hl
-	push	de
-	push	bc
-	ld	c, #2		; SYS_READ
+	ld	c, #2			; SYS_READ
 	rst	#0x30
-	pop	bc
-	pop	de
-	pop	hl
 	ret
-	;; void sexit(unsigned char code /*A*/)
+
+	;; void sexit(unsigned char code /*A*/) - never returns
 _sexit:
 	ld	b, a
-	ld	c, #0		; SYS_EXIT
+	ld	c, #0			; SYS_EXIT
 	rst	#0x30
 	ret
+
 	;; unsigned char getpid(void) -> A
 _getpid:
-	push	hl
-	push	de
-	push	bc
-	ld	c, #8		; SYS_GETPID
+	ld	c, #8			; SYS_GETPID
 	rst	#0x30
-	pop	bc
-	pop	de
-	pop	hl
 	ret
diff --git a/c/pid.c b/c/pid.c
new file mode 100644
index 0000000..a282a89
--- /dev/null
+++ b/c/pid.c
@@ -0,0 +1,9 @@
+#include "gbos.h"
+/* print an unsigned byte as decimal (no runtime division: subtract-based) */
+static void putu(unsigned char n) {
+    char buf[3]; unsigned char i = 0;
+    if (n == 0) { putc('0'); return; }
+    while (n) { buf[i++] = '0' + (n % 10); n = n / 10; }
+    while (i) putc(buf[--i]);
+}
+void main(void) { putu(getpid()); nl(); }
diff --git a/c/true.c b/c/true.c
new file mode 100644
index 0000000..4cf437e
--- /dev/null
+++ b/c/true.c
@@ -0,0 +1,2 @@
+#include "gbos.h"
+void main(void) { sexit(0); }
diff --git a/c/uname.c b/c/uname.c
new file mode 100644
index 0000000..511501d
--- /dev/null
+++ b/c/uname.c
@@ -0,0 +1,2 @@
+#include "gbos.h"
+void main(void) { puts("gbos sm83 (Game Boy Color)"); nl(); }
-- 
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