Aligned structures using "struc"

(repost from here)

recently i had funny alignment problem with FASM.

I had structure, let's say STRUC1

Code:

struc STRUC1 x,y,z{
.x dd x+0
.y dd y+0
.z db z+0
}

I wanted to align it

Code:

struc STRUC1 x,y,z{
.x dd x+0
.y dd y+0
.z db z+0
align 4  ;<----
}

This worked nicely, structure size was aligned. Later, I "overloaded" it with STRUC2:

Code:

struc STRUC2 x,y,z,xx,yy,zz{
. STRUC1 x,y,z
.xx dd xx+0
.yy dd yy+0
.zz db zz+0
align 4
}

This seemed to work too, until once i found that some data of intialized STRUC2 structure were shifted by two bytes against where they should be. It took me nearly hour and half to realize what is happening:

the initialized structure was being declared on unaligned offset. so the resulting declaration (after preprocessing of struct) looked like:

Code:

; jano  STRUC2  1,2,3,4,5,6
jano:
.x dd 1
.y dd 2
.z db 3
align 4
.xx dd 4
.yy dd 5
.zz db 6
align 4

first members of structure were declared unaligned, until first align was reached.

So for every structure with aligned members in FASM, also align the structure itself, like this:

Code:

struc STRUC1 x,y,z{
align 4
.:
.x dd x+0
.y dd y+0
.z db z+0
align 4
}

but of course, it's always better to use standard STRUCT macros.