Print Page - alignment declared in structure don't work

Title: alignment declared in structure don't work
Post by: ToutEnMasm on February 08, 2008, 02:41:13 PM

Hello,
I try to align a structure as follow

Quote
   .486
   .model flat, stdcall
   option casemap :none ; case sensitive
;............. include,...
LKEYDATA STRUCT 16
;another maner to write a record
RepeatCount DD (1111111111111111b    SHL 0)
ScanCode     DD (11111111b       SHL 16)
ExtendedKey DD (1b         SHL 24)
Reserved DD (1111b         SHL 25)
ContextCode DD (1b         SHL 29)
PreviousKeyState DD (1b         SHL 30)
TransitionState DD (1b         SHL 31)
LKEYDATA ENDS
.data
onebyte db 0
;---- here align 16 work
clavier LKEYDATA <>
.code
lea eax,infoclav      ;41c008
xor edx,edx
mov ecx,16
div ecx
.if edx != 0
invoke MessageBox,NULL,SADR("LKEYDATA bad Alignement"),SADR("infoclav"),MB_OK
.endif

invoke exitprocess,NULL

Any idea ?

Title: Re: alignment declared in structure don't work
Post by: MichaelW on February 08, 2008, 05:32:03 PM

AFAIK the only valid values for the alignment are 1, 2, and 4, the actual alignment is the minimum of the field size and the specified alignment, and this applies only to the alignment between the fields in the structure. To control the alignment of the structure in memory you must align the data definition. You can also control the alignment between the fields in the structure by placing alignment directives in the structure declaration. So this structure declaration:

Code Select


    LKEYDATA STRUCT 
      ;another maner to write a record
      RepeatCount       DD (1111111111111111b SHL 0)
      align 16
      ScanCode          DD (11111111b SHL 16)
      align 16
      ExtendedKey       DD (1b SHL 24)
      align 16
      Reserved          DD (1111b SHL 25)
      align 16
      ContextCode       DD (1b SHL 29)
      align 16
      PreviousKeyState  DD (1b SHL 30)
      align 16
      TransitionState   DD (1b SHL 31)
    LKEYDATA ENDS

Combined with this data definition:

Code Select


      align 16
      clavier LKEYDATA <>

Should ensure that all of the fields will be aligned on a 16-byte boundary.

Title: Re: alignment declared in structure don't work
Post by: ToutEnMasm on February 08, 2008, 06:20:22 PM

I have written a macro for testing the alignment.
Something put me on trouble.
Using ml /Zp4 must align the structures,don't work also

Quote
.data
onebyte db 0
clavier LKEYDATA <> ;isn't align to 4 by ml /Zp4

Quote
   TESTALIGN MACRO argument
   Local findesalign
   lea eax,argument
   xor edx,edx
   mov ecx,16
   div ecx
   .if edx == 0
      invoke MessageBox,NULL,SADR("16"),SADR("Alignment 16"),MB_OK
      jmp findesalign
   .endif
   lea eax,argument
   xor edx,edx
   mov ecx,8
   div ecx
   .if edx == 0
      invoke MessageBox,NULL,SADR("QWORD"),SADR("Alignment 8"),MB_OK
      jmp findesalign
   .endif
   lea eax,argument
   xor edx,edx
   mov ecx,4
   div ecx
   .if edx == 0
      invoke MessageBox,NULL,SADR("DWORD"),SADR("Alignment 4"),MB_OK
      jmp findesalign
   .endif
   lea eax,argument
   xor edx,edx
   mov ecx,2
   div ecx
   .if edx == 0
      invoke MessageBox,NULL,SADR("WORD"),SADR("Alignment 2"),MB_OK
      jmp findesalign
   .endif
   lea eax,argument
   xor edx,edx
   mov ecx,1
   div ecx
   .if edx == 0
      invoke MessageBox,NULL,SADR("BYTE"),SADR("Alignment 1"),MB_OK
      jmp findesalign
   .endif
   findesalign:
   ENDM

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