From bcb4f66286476d6697c1f363a41eb167c958b40a Mon Sep 17 00:00:00 2001
From: "B. Watson" <urchlay@slackware.uk>
Date: Tue, 28 May 2024 15:38:08 -0400
Subject: unprotbas: -p/-pc now actually inserts a new line of code with the
 bad offset.

---
 unprotbas.1   |  6 +++---
 unprotbas.c   | 40 +++++++++++++++++++++++++++++++---------
 unprotbas.rst |  6 +++---
 3 files changed, 37 insertions(+), 15 deletions(-)

diff --git a/unprotbas.1 b/unprotbas.1
index 1e1b919..b8123f1 100644
--- a/unprotbas.1
+++ b/unprotbas.1
@@ -228,9 +228,9 @@ The program \fBUNPROTEC\fP, from the \fIPirate\(aqs Treasure Chest\fP, can
 fix bad pointers in protected programs, though it doesn\(aqt do
 anything about variable name scrambling.
 .sp
-\fBunprotbas \-pc\fP also does this type of protection. Beware: the
-last line of code must never actually be executed by the program,
-or BASIC will freeze when it tries to execute it.
+\fBunprotbas \-pc\fP also does this type of protection. It works by
+adding a line 32767 to the program, with a bad next\-line pointer.
+This will fail if there\(aqs already a line 32767.
 .UNINDENT
 .sp
 One more thing \fBunprotbas\fP can do is remove extra data from the end
diff --git a/unprotbas.c b/unprotbas.c
index efc1b2f..6edb38f 100644
--- a/unprotbas.c
+++ b/unprotbas.c
@@ -40,6 +40,15 @@
 /* entire file gets read into memory (for now) */
 unsigned char data[BUFSIZE];
 
+/* for the -p/-pc options: 32767 END */
+unsigned char badcode[] = {
+	0xff, 0x7f,   /* line number 32767      */
+	0x00,         /* *bad* next-line offset */
+	0x06,         /* next-statement offset  */
+	0x15,         /* END token              */
+	0x16,         /* end-of-line token      */
+};
+
 /* for the -r option */
 #define MAP_FILE "varnames.txt"
 unsigned char varnames[BUFSIZE];
@@ -200,7 +209,7 @@ int fixcode(void) {
 		offset = data[pos + 2];
 		/* fprintf(stderr, "pos %d, line #%d, offset %d\n", pos, lineno, offset); */
 		if(offset < 6) {
-			if(verbose) fprintf(stderr, "Found invalid offset %d (<6) at line %d, file offset %04x\n", offset, lineno, pos + 2);
+			if(verbose) fprintf(stderr, "Found invalid offset %d (<6) at line %d, file offset %04x\n", offset, lineno, pos);
 			offset += fixline(pos);
 			result++;
 		}
@@ -222,7 +231,7 @@ int fixcode(void) {
 	return result;
 }
 
-/* iterate over all the lines, zero out the offset of the last one
+/* iterate over all the lines, insert a poisoned line 32767 just
 	before line 32768 */
 void breakcode(void) {
 	int pos = codestart, oldpos = 0;
@@ -244,13 +253,26 @@ void breakcode(void) {
 		}
 	}
 
-	if(!oldpos) {
-		die("can't protect code because there are no lines of code");
-	} else {
-		data[oldpos + 2] = 0;
-		if(verbose)
-			fprintf(stderr, "set invalid line length 0 at line %d, file offset %04x\n", lineno, oldpos + 2);
-	}
+	if(!oldpos) die("can't protect code because there are no lines of code");
+	if(lineno == 32767) die("can't protect code because there is already a line 32767");
+
+	/* pos is now the start of line 32768, move it up to make room for
+		the new line */
+	offset = sizeof(badcode);
+	memmove(data + pos + offset, data + pos, filelen);
+
+	/* insert new line */
+	memmove(data + pos, badcode, offset);
+
+	if(verbose)
+		fprintf(stderr, "Inserted line 32767 with invalid offset at file offset %04x\n", pos);
+
+	/* update pointers that would be affected by the code move */
+	stmcur += offset;
+	starp += offset;
+	set_header_vars();
+	read_header();
+	filelen += offset;
 }
 
 /* sometimes the variable name table isn't large enough to hold
diff --git a/unprotbas.rst b/unprotbas.rst
index cf7ca84..1df865f 100644
--- a/unprotbas.rst
+++ b/unprotbas.rst
@@ -202,9 +202,9 @@ Bad next-line pointer
   fix bad pointers in protected programs, though it doesn't do
   anything about variable name scrambling.
 
-  **unprotbas -pc** also does this type of protection. Beware: the
-  last line of code must never actually be executed by the program,
-  or BASIC will freeze when it tries to execute it.
+  **unprotbas -pc** also does this type of protection. It works by
+  adding a line 32767 to the program, with a bad next-line pointer.
+  This will fail if there's already a line 32767.
 
 One more thing **unprotbas** can do is remove extra data from the end
 of the file. It's possible for BASIC files to contain extra data that
-- 
cgit v1.2.3