From bd9a62c1ce3355c59d76439904d45dd56da5d6e3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Juhani=20Krekel=C3=A4?= <juhani@krekelä.fi>
Date: Thu, 23 Mar 2023 18:27:40 +0200
Subject: [PATCH] Properly access directory when launching files

---
 ponydos_static.inc |  2 ++
 shell.asm          | 16 ++++++++++++----
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/ponydos_static.inc b/ponydos_static.inc
index 58cb2cf..7775791 100644
--- a/ponydos_static.inc
+++ b/ponydos_static.inc
@@ -5,6 +5,8 @@ GLOBAL_DIRENTS equ 0x2000
 
 FS_DIRENT_SIZE equ 32
 FS_DIRENT_NAME_SIZE equ 30
+FS_DIRENT_NAME_OFFSET equ 2
+FS_DIRECTORY_DIRENTS equ 512/FS_DIRENT_SIZE
 FS_FILE_MAX_SIZE equ 128
 
 COLUMNS equ 80
diff --git a/shell.asm b/shell.asm
index 5659e59..f3f9799 100644
--- a/shell.asm
+++ b/shell.asm
@@ -396,6 +396,8 @@ click:
 		sub ax, [si + window.y]
 		jz .end
 		dec ax
+		cmp ax, FS_DIRECTORY_DIRENTS
+		jae .end
 
 		push ds
 
@@ -406,9 +408,15 @@ click:
 		mul bp
 		mov si, GLOBAL_DIRENTS
 		add si, ax
-		add si, 2 ; File name begins two bytes into the start of the dirent
+
+		cmp word [si], 0
+		jne .dirent_present
+		pop ds
+		jmp .end
+		.dirent_present:
 
 		; Copy file name to launch_filename
+		add si, FS_DIRENT_NAME_OFFSET
 		mov di, launch_filename
 		mov cx, FS_DIRENT_NAME_SIZE
 		rep movsb
@@ -752,11 +760,11 @@ print_ls:
 
 	push cx
 	push di
-	mov si, GLOBAL_DIRENTS + 2
+	mov si, GLOBAL_DIRENTS + FS_DIRENT_NAME_OFFSET
 
 	xor ax, ax ; Maximum filename size
 	.name_loop:
-		cmp word [ds:si - 2], 0
+		cmp word [ds:si - FS_DIRENT_NAME_OFFSET], 0
 		je .done_names
 
 		push cx
@@ -789,7 +797,7 @@ print_ls:
 		add di, dx
 
 		add si, FS_DIRENT_SIZE
-		cmp si, GLOBAL_DIRENTS + 0x200
+		cmp si, GLOBAL_DIRENTS + FS_DIRECTORY_DIRENTS*FS_DIRENT_SIZE
 		jge .done_names
 
 		dec cx