ansaurus

Question

Answer 1

+4 A:

You need to diagnose your crash.

Install and setup DrWatson so that it catches crash data.
run ML again with options to output a pdb file
trigger the crash again - you DrWatson should trap it.

Alternative: Run your program through a debugger. Since VS 2008, VS has MASM (ML) built-in, so you might even be able to get source debugging. I documented activating MASM in VS 2008 Express SP1 - free - (and presumably following versions) there. Otherwise, use windbg (not as friendly).

Now I didn't go at all through your algorithm, but the way you use ESP kinda scares me: Are you REALLY sure ESP still points to your PUSHAD stack-based save area when you execute the POPAD in SORT_ARRAY?...

I have programmed and maintained very large software pieces using ML, and my recommendation would be to never messup with ESP, and let MASM take care of (E)BP in most circumstances. The only exceptions relate to heavy systems programming, like bitness mode changing (entering / leaving prot mode) and implementing a threading monitor (state saving / restoration).

A few others:
Don't use jumps anymore, use .IF / .ELSE / .ENDIF, .REPEAT / .WHILE / .UNTIL, etc. and the like.
Don't bother with EBP for parms and local vars, let ML pseudo-ops take care of parms and local variable addressing. Use MASM-managed parameter passing (through INVOKE instead of CALL) and use MASM-managed local variables (through the LOCAL in-PROC directive). You can even define arrays in LOCAL with a syntax such as

Foo[6]: BYTE

In the sample that follows:
CheckRAMPresent is called with two DWORD Parms, LinBufferBase and BufferSize.
Upon entry and exit, MASM saves and restore EAX ECX EBX DI ES because I told it the PROC uses it.
SMAPBuffer, RAMBank and RAMBankEnd are local (stack based) variables (SMPOutput is a STRUCT). MASM manipulates the stack pointer to allocated / deallocate upon entry / exit, and manages the BP-based address mode - see how the code in the PROC addresses both the parms and the local vars.
Finally, you have examples of .IF .ELSE .ENDIF and even a .REPEAT / .UNTIL
Note that you can use condition flags

.IF CARRY?

or HLL-like condition expressions:

(ES:[DI].RangeType == 1)

or even the more complex:

((ECX >= EAX) && (ECX <= EBX)) || ((EDX >= EAX) && (EDX <= EBX))

Those generate totally predictable code, so this is still assembly language. But it's just a much more readable / maintainable kind of assembly. For all the HLL pseudo-ops, look at the generated code (there's an ML option for that).

The whole set of MASM documentation explaining the HLL constructs can be found there in ZIPped .doc & HTML formats. You can find it elsewere in PDF form, methinks (Google around). The Programmer's Guide is by far the most useful part. The MASM reference manual is mostly obsolete, you'd rather use the Intel developer's guide instead.

CheckRAMPresent PROC NEAR STDCALL PUBLIC \
                 USES EAX ECX EBX DI ES,
                   LinBufferBase: DWORD,
                   BufferSize:    DWORD

               LOCAL SMAPBuffer: SMAPOutput,
                   RAMBank:      DWORD,
                   RAMBankEnd:   DWORD


 MOV AX,SS                   ; Get ES:DI => SMAP buffer,
 MOV ES,AX
 LEA DI, SMAPBuffer
 MOV ECX, SIZEOF SMAPBuffer  ;  ECX = SMAP buffer size.

 PUSHCONTEXT ASSUMES
 ASSUME DI:PTR SMAPOutput

 XOR EBX,EBX                 ; Set initial continuation pointer.
 MOV RAMBank, EBX            ; Zero the RAM bank tracker.
 MOV RAMBankEnd, EBX

   .REPEAT
   INVOKE GetSMAP
   .BREAK .IF CARRY?
     ; If type is Available, then process that range.
     .IF (ES:[DI].RangeType == 1) ; If Available RAM, check what we have.
     SAVE EBX, ECX
     MOV EAX, ES:[DI].LowBase    ; Get Bank start in EAX,
     MOV EBX, EAX
     ADD EBX, ES:[DI].LowLng     ;   and bank end in EBX.
     MOV ECX, LinBufferBase      ; Get buffer start in ECX
     MOV EDX,ECX
     ADD EDX, BufferSize         ;  and buffer end in EDX.

       ; If either the lower end or the upper end of the buffer
       ; intersects with the bank, take that bank (if this is the
       ; first) or try to coalesce it with the existing one (if we already
       ; have one).
       ; This translates as:
       ; If either the low address (ECX) or the high address (EDX) of the
       ; buffer is within the bank boundaries [EAX - EBX], then the buffer
       ; intersects with the bank.
       .IF   ((ECX >= EAX) && (ECX <= EBX)) \ ; If buffer intersects,
          || ((EDX >= EAX) && (EDX <= EBX))
         ; then if this is the first intersecting RAM bank, too, then
select it.
         .IF (!RAMBank && !RAMBankEnd)
         MOV RAMBank, EAX    ; Remember bank.
         MOV RAMBankEnd, EBX
         .ELSE
         ; We already have a RAM bank.
           ; If this new one starts where the one we have ends,
           ; the end of the new one become the end of the merged blocks.
           ; Else if the end of the new block is the beginning of the one
           ; we have, then the new block is located just before the one we
           ; have and its start become the start of the merged blocks.
           ; Otherwise, the new bank is not contiguous with the previously
           ; computed one and there's nothing we can do (at least using this
           ; algorithm).
           .IF (EAX == RAMBankEnd)
           MOV RAMBankEnd, EBX
           .ELSEIF (EBX == RAMBank)
           MOV RAMBank, EAX
           .ENDIF
         .ENDIF
       .ENDIF
     RESTORE EBX, ECX
     .ENDIF

   .UNTIL (EBX == 0)         ; If SMAP returned EBX == 0, we just did the
                             ; last SMAP bank.

 MOV EAX, LinBufferBase      ; Get buffer start in EAX
 MOV ECX,EAX
 ADD ECX, BufferSize         ;  and buffer end in ECX.

   ; If our start and our end are both in the bank,
   ; we win. Otherwise, we loose.
   .IF (EAX >= RAMBank) && (ECX <= RAMBankEnd)
   CLC
   .ELSE
   STC
   .ENDIF

 RET
CheckRAMPresent ENDP

Have fun! ;-)

filofel 2010-10-27 08:01:17

ansaurus

tags:

views:

answers:

selection sort in assembly language

related questions