Remove dependence on perl, depend on python instead

Makefile

@@ -96,8 +96,8 @@ _%: %.o $(ULIB)
 	$(OBJDUMP) -S $@ > $*.asm
 	$(OBJDUMP) -t $@ | sed '1,/SYMBOL TABLE/d; s/ .* / /; /^$$/d' > $*.sym
 
-$U/usys.S : $U/usys.pl
-	perl $U/usys.pl > $U/usys.S
+$U/usys.S : $U/usys.py
+	python3 $U/usys.py > $U/usys.S
 
 $U/usys.o : $U/usys.S
 	$(CC) $(CFLAGS) -c -o $U/usys.o $U/usys.S

user/usys.pl

@@ -1,40 +0,0 @@
-#!/usr/bin/perl -w
-
-# Generate usys.S, the stubs for syscalls.
-
-print "# generated by usys.pl - do not edit\n";
-
-print "#include \"kernel/syscall.h\"\n";
-
-sub entry {
-    my $name = shift;
-    print ".global $name\n";
-    print "${name}:\n";
-    print " li a7, SYS_${name}\n";
-    print " ecall\n";
-    print " ret\n";
-}
-
-entry("fork");
-entry("exit");
-entry("wait");
-entry("pipe");
-entry("read");
-entry("write");
-entry("close");
-entry("kill");
-entry("exec");
-entry("open");
-entry("mknod");
-entry("unlink");
-entry("fstat");
-entry("link");
-entry("mkdir");
-entry("chdir");
-entry("dup");
-entry("getpid");
-entry("sbrk");
-entry("sleep");
-entry("uptime");
-entry("trace");
-entry("halt");

user/usys.py

@@ -0,0 +1,47 @@
+#!/usr/bin/env python3
+
+template = """.global {name}
+{name}:
+    li a7, SYS_{name}
+    ecall
+    ret"""
+
+
+def genstub(syscall: str):
+    return template.format(name=syscall)
+
+
+syscalls = [
+    "fork",
+    "exit",
+    "wait",
+    "pipe",
+    "read",
+    "write",
+    "close",
+    "kill",
+    "exec",
+    "open",
+    "mknod",
+    "unlink",
+    "fstat",
+    "link",
+    "mkdir",
+    "chdir",
+    "dup",
+    "getpid",
+    "sbrk",
+    "sleep",
+    "uptime",
+    "trace",
+    "halt",
+]
+
+assembly = "\n\n".join(map(genstub, syscalls))
+
+# TODO: Perhaps do some more specific assertions on the code here
+assert len(assembly) > 0, "No assembly code generated. Something is fishy"
+
+print("# generated by usys.py - do not edit\n")
+print('#include "kernel/syscall.h"\n')
+print(assembly)