From e8fb22c826a84008654b6ce78ec6641cb6fc4e5b Mon Sep 17 00:00:00 2001
From: Elaina Claus <elaina.claus@chtm.me>
Date: Fri, 11 Oct 2024 14:25:01 -0400
Subject: [PATCH] somewhat of a cludge, but added a macro to save all caller
 saved regs

---
 include/cdecl16.inc         | 16 ++++++++++++++++
 include/fat32/FAT32_SYS.inc | 24 +++++++++++++++++++++---
 2 files changed, 37 insertions(+), 3 deletions(-)

diff --git a/include/cdecl16.inc b/include/cdecl16.inc
index 81477e8..60583ad 100644
--- a/include/cdecl16.inc
+++ b/include/cdecl16.inc
@@ -38,4 +38,20 @@
     mov sp, bp
     pop bp
 %endmacro
+%endif
+
+%ifnmacro __CDECL16_CALLER_SAVE
+%macro __CDECL16_CALLER_SAVE 0
+    push ax
+    push cx
+    push dx
+%endmacro
+%endif
+
+%ifnmacro __CDECL16_CALLER_RESTORE
+%macro __CDECL16_CALLER_RESTORE 0
+    pop dx
+    pop cx
+    pop ax
+%endmacro
 %endif
\ No newline at end of file
diff --git a/include/fat32/FAT32_SYS.inc b/include/fat32/FAT32_SYS.inc
index 70d91ac..902d887 100644
--- a/include/fat32/FAT32_SYS.inc
+++ b/include/fat32/FAT32_SYS.inc
@@ -91,6 +91,8 @@ SearchFATDIR:
         mov eax, [fat32_ebpb + FAT32_ebpb_t.root_dir_cluster_32]
         mov dword [fat32_state + FAT32_State_t.active_dir_cluster_32], eax
 
+        __CDECL16_CALLER_SAVE
+
         push dword eax          ; cluster
         lea ax, [dir_buffer]
         push ax                 ; offset
@@ -99,16 +101,20 @@ SearchFATDIR:
         call ReadFATCluster     ; uint8_t ReadFATCluster(uint16_t seg, uint16_t offset, uint32_t cluster)
         add sp, 0x8
 
+        __CDECL16_CALLER_RESTORE
+
         lea si, [dir_buffer]
         jmp SearchFATDIR.empty_dir_entry
 
     .load_next_dir:
         ; if eax >= 0x0FFFFFF8 then there are no more clusters (end of chain)
         ; if eax == 0x0FFFFFF7 then this is a cluster that is marked as bad
+        __CDECL16_CALLER_SAVE
         mov eax, dword [fat32_state + FAT32_State_t.active_dir_cluster_32]
         push dword eax
         call NextCluster        ; uint32_t NextCluster(uint32_t active_cluster);
         add sp, 0x4
+        __CDECL16_CALLER_RESTORE
 
         cmp eax, 0x0fff_fff7
         jb SearchFATDIR.load_next_dir_next_OK
@@ -116,15 +122,18 @@ SearchFATDIR:
 
     .load_next_dir_next_OK:
         ; load 512 bytes of directory entries from data sector
+        __CDECL16_CALLER_SAVE
         mov eax, [fat32_state + FAT32_State_t.active_dir_cluster_32]
+        push dword eax          ; cluster
 
-        push dword eax
-        lea ax, [dir_buffer]    ; cluster
+        lea ax, [dir_buffer]    
         push ax                 ; offset
+
         xor ax, ax
         push ax                 ; segment
         call ReadFATCluster     ; uint8_t ReadFATCluster(uint16_t seg, uint16_t offset, uint32_t cluster)
         sub sp, 0x8
+        __CDECL16_CALLER_RESTORE
 
         lea si, [dir_buffer]
     .empty_dir_entry:
@@ -181,7 +190,7 @@ SearchFATDIR:
 .endp:
     __CDECL16_EXIT
     ret
-
+; BUG: this function needs review
 ; uint32_t NextCluster(uint32_t active_cluster);
 ; if eax >= 0x0FFFFFF8 then there are no more clusters (end of chain)
 ; if eax == 0x0FFFFFF7 then this is a cluster that is marked as bad
@@ -232,6 +241,7 @@ NextCluster:
     add eax, ecx        ; fat_sector + first_fat_sector
     mov dword [si + FAT32_NextClusterData_t.fat_sector], eax
 .load_fat_table:
+    __CDECL16_CALLER_SAVE
     movzx ax, [bp - 2]
     push ax
 
@@ -249,6 +259,7 @@ NextCluster:
     push ax
     call read_disk_raw  
     add sp, 0xC
+    __CDECL16_CALLER_RESTORE
     ; uint8_t read_stage2_raw(uint16_t buf_segment, uint16_t buf_offset, 
 ;                         uint32_t lba,
 ;                         uint16_t count, uint16_t drive_num)
@@ -281,6 +292,7 @@ ALIGN 4, db 0x90
 ReadFATCluster:
     __CDECL16_ENTRY
 .func:
+    __CDECL16_CALLER_SAVE
     mov bx, [boot_drive_ptr]
     mov ax, [bx + 0]
     mov byte [bp - 2], al                        ; save boot drive as a local for easy access
@@ -290,7 +302,9 @@ ReadFATCluster:
     call ClusterToLBA    ; uint32_t ClusterToLBA(uint32_t cluster)
     add sp, 0x4         ; eax == LBA
     mov dword [bp - 6], eax
+    __CDECL16_CALLER_RESTORE
 
+    __CDECL16_CALLER_SAVE
     movzx ax, [bp - 2]
     push ax
 
@@ -305,8 +319,12 @@ ReadFATCluster:
 
     xor ax, ax
     push ax
+; uint8_t read_stage2_raw(uint16_t buf_segment, uint16_t buf_offset, 
+;                         uint32_t lba,
+;                         uint16_t count, uint16_t drive_num)
     call read_disk_raw  
     add sp, 0xC
+    __CDECL16_CALLER_RESTORE
 .endp:
     __CDECL16_EXIT
     ret