add cat

.gitignore

@@ -1,2 +1,3 @@
 /true
 /false
+/cat

Makefile

@@ -4,8 +4,9 @@ LD = $(TARGET)-ld
 
 .SUFFIXES:
 
-all: true false
-#all: cat echo
+.PHONY: all
+all: true false cat
+#all: echo
 
 %: %.o
 	$(LD) -o $@ $<

cat.s

@@ -0,0 +1,68 @@
+.globl _start
+.option rvc # enable compressed instructions
+
+.data
+sigaction_ignore:
+    .dword 1 # sa_handler = SIG_IGN
+    .dword 0 # sa_flags
+    .dword 0  # sa_mask
+
+.bss
+.equ bufsize, 4<<10
+buf: .zero bufsize
+
+.text
+_start:
+    # ignore SIGPIPE
+    li a7, 134  # sys_rt_sigaction
+    li a0, 13   # SIGPIPE
+    la a1, sigaction_ignore # action
+    li a2, 0    # oldact = NULL
+                # if this is a non-null pointer the kernel will
+                # return a copy of the old action to us, but we don't care
+    li a3, 8    # signal set size (bytes)
+    ecall
+
+# TODO: cat args
+# TODO: error messages
+
+loop:
+    li a7, 63      # sys_read
+    li a0, 0       # fd = stdin
+    la a1, buf     # pointer to buffer
+    li a2, bufsize  # size of buffer
+    ecall
+    #li a0, 0
+
+    # return in a0
+    #   negative => error code
+    #   positive => number of byte read
+    #   zero     => end of input
+    bltz a0, error
+    beqz a0, done
+
+    mv s0, a0
+
+    li a7, 64      # sys_write
+    li a0, 1       # fd = stdout
+    la a1, buf     # pointer to string
+    mv a2, s0      # size of data
+    ecall
+
+    beq a0, s0, loop
+    # error, fall through
+
+    # check for EPIPE
+    li t0, -32
+    beq a0, t0, done # EPIPE
+
+error:
+    li a7, 93 # sys_exit
+    li a0, 1  # status code = failure
+    ecall
+
+done:
+    li a7, 93 # sys_exit
+    li a0, 0  # status code = success
+    ecall
+