diff --git a/amogus.h b/amogus.h
index 714565b..4cab2c3 100644
--- a/amogus.h
+++ b/amogus.h
@@ -1 +1,15 @@
-int entry(char* regex, char** output);
+// int entry(...)
+//
+// Parse regex. Find matching string.
+// If found:
+//   call callback(
+//     matched string (only valid before callback return),
+//     length of the string including NUL delimiter,
+//     data passed in the data argument
+//   )
+//   return 0
+// Else:
+//   return 1
+
+typedef void (entry_callback)(char* match, int size, void* data);
+int entry(char* regex, entry_callback *callback, void *data);
diff --git a/meow.s b/meow.s
index 6addb5e..48e1f59 100644
--- a/meow.s
+++ b/meow.s
@@ -10,11 +10,11 @@ _start:
 	pop %rax
 	mov %rax,argv(%rip)
 	cmp $1,%rdi
-	jg endif
+	jg _start_endif
 	mov $1,%rdi
 	call usage
 	jmp _exit
-endif:
+	_start_endif:
 	
 	mov $0,%rdi
 	jmp _exit
@@ -58,17 +58,33 @@ write:
 	mov $1,%rdi
 	syscall
 	ret
+
 help0:
 	.ascii "Usage: "
 	.set help0l, .-help0
 help1:
 	.ascii " regex0 [regex1 ...]\nstdout: NUL-separated list of matching strings\n"
 	.set help1l, .-help1
+
+# rdi - exit code
 _exit:
 	mov $0x3c,%rax
 	syscall
 	ret
+
 entry:
+	push %r12
+	sub $8,%r12
+	mov %rsp,%r12
+	entry_parse_begin:
+		test %rdi,%rdi
+		jnz entry_parse_end
+		mov %rdi,%rcx
+		inc %rdi
+	entry_parse_end:
+	mov %r12,%rsp
+	add $8,%r12
+	pop %r12
 	ret
 
 .bss
@@ -76,5 +92,3 @@ argc:
 	.zero 8
 argv:
 	.zero 8
-buf:
-	.zero 65536
diff --git a/test.c b/test.c
index c2fee51..87943c5 100644
--- a/test.c
+++ b/test.c
@@ -1,9 +1,17 @@
 #include <amogus.h>
 #include <stdio.h>
+#include <stdlib.h>
+#include <memory.h>
+
+void callback(char* str, int size, void* data) {
+	char** out = (char**)data;
+	*out = (char*)malloc(size);
+	memcpy(str, *out, size);
+}
 
 int main() {
 	char* match;
-	if(!entry("meow.*|m(r(r(p..*)))",&match))
+	if(!entry("meow.*|m(r(r(p..*)))",callback,&match))
 		return 1;
 	printf("%s",match);
 }