mtdbg: Check ebp for 0 instead of check initial esp

Signed-off-by: Max Logaev <maxlogaev@proton.me>

programs/develop/mtdbg/mtdbg.asm

@@ -240,10 +240,6 @@ do_reload:
         mov     ecx, (ctx_end-context)/4
         rep movsd
 
-    ; Save initial stack pointer 
-        mov     ecx, [_esp]
-        mov     [start_esp], ecx
-
     ; activate debugger window
         pop     ecx
         mcall   18, 3
@@ -1156,8 +1152,8 @@ OnDump:
 ;                            Print Backtrace
 
 struct STACK_FRAME
-        _ebp       rd 1
-        _eip       rd 1
+        prev_frame      rd 1
+        ret_addr        rd 1
 ends
 
 OnBacktrace:
@@ -1189,12 +1185,6 @@ OnBacktrace:
         test    ebp, ebp
         jz      .done
 
-        ; The frame must be within the stack
-        mov     eax, [start_esp]
-        sub     eax, sizeof.STACK_FRAME
-        cmp     ebp, eax
-        ja      .done
-
         mov     edi, stack_frame_dump
 
     .next:
@@ -1203,24 +1193,29 @@ OnBacktrace:
         mov     esi, read_mem_err
         jz      .exit
 
+        ; The address of the previous frame must be less than the current one
+        mov     eax, [edi + STACK_FRAME.prev_frame]
+        test    eax, eax
+        jz      .done
+
         ; Save stack_frame_dump
         push    edi
-        ; Save EBP
+        ; Save previous frame
         push    ebp
-        ; Save EIP
-        mov     eax, [edi + STACK_FRAME._eip]
+        ; Save return address
+        mov     eax, [edi + STACK_FRAME.ret_addr]
         push    eax
 
-        ; Print EBP and EIP
+        ; Print frame address and return address
         push    eax         ; pop in put_message_nodraw
         push    ebp         ; pop in put_message_nodraw
         mov     esi, aBacktraceFmt
         call    put_message_nodraw
 
-        ; Restore EIP
+        ; Restore return address
         pop     eax
 
-        ; Find symbol by EIP
+        ; Find symbol by return address
         call    find_near_symbol
         test    esi, esi
         jz      .print_stub
@@ -1238,23 +1233,17 @@ OnBacktrace:
         mov     esi, newline
         call    put_message_nodraw
 
-        ; Restore EBP
+        ; Restore previous frame
         pop     ebp
         ; Restore stack_frame_dump
         pop     edi
 
-        ; The address of the next frame must be greater than the previous one
-        cmp     [edi + STACK_FRAME._ebp], ebp
-        jbe     .done
+        ; The address of the previous frame must be greater than the current one.
+        cmp     [edi + STACK_FRAME.prev_frame], ebp
+        jna     .done
 
-        ; The frame must be within the stack
-        mov     eax, [start_esp]
-        sub     eax, sizeof.STACK_FRAME
-        cmp     [edi + STACK_FRAME._ebp], eax
-        ja      .done
-
-        ; Set next frame
-        mov     ebp,  [edi + STACK_FRAME._ebp]
+        ; Set previous frame
+        mov     ebp,  [edi + STACK_FRAME.prev_frame]
         dec     [bt_depth]
         jnz     .next
 
@@ -2628,7 +2617,6 @@ disasm_cur_pos          dd ?
 disasm_cur_str          dd ?
 disasm_string           rb 256
 
-start_esp               rd 1
 stack_frame_dump        rb sizeof.STACK_FRAME
 bt_depth                rd 1
 prev_bt_sym             rd 1