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Index > Compiler Internals > Suggestions on 'strict-ness' of FASM

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Joined: 28 Jan 2004
Posts: 1590
Location: Toronto, Canada
AsmGuru62 29 Dec 2011, 13:43
Hi everyone,

Lately I was writing a lot of code and I made some 'blunders'.
Now, that I thought about it -- FASM as a compiler could warn me of a code situations, which are probably incorrect.
I wonder if FASM has any warnings right now in its arsenal.
I know that HLLs have quite a bit of warnings -- protecting the programmer, so to speak.

So, I have two warning suggestions.

First is about the 'virtual' directive.
Say, I have the following statement:
virtual at 0
    .Field1  dd ?
       .Field2  rd 16
      .Field3  rw 32
      .size = $
end virtual

Now, somewhere in my code I want to point my register at TApplication.Field3:
mov ebx, [glb_pApp]             ; points to instance of TApplication
lea esi, [ebx + TApplication]   ; <-- Here I forgot the ".Field3"
; The above is incorrect!
; The below is what I needed.
lea       esi, [ebx + TApplication.Field3]

Now, the debugger shows that label from a virtual statement evaluates to 0 and that is fine, however it would have been nice if FASM can warn about a situation where the label is used without a field.

Second is about the anonymous label ("@@:" <-- this one!).
Usually, these labels are good in short distances. When the distance increases -- there is a possibility of a mistake to be made. The code usually contains procedures and it would be nice if FASM could warn if a target for anonymous JMP (@f,@r) is located in another procedure:
  test    eax, eax
    jz      @f
 test    eax, eax
    jz      @f
 ...     ; <-- Somewhere here is forgotten '@@:'

  mov     ecx, 256
@@:             ; <-- Code from Procedure1 will fall here!
 loop    @r
Post 29 Dec 2011, 13:43
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When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20220
Location: In your JS exploiting you and your system
revolution 29 Dec 2011, 13:52
I have two simple solutions for your two problems:

1. Don't use virtual for structures. Use struc, that is what it is for.

2. Don't use @@ anywhere. It is just a lazy way to create a label and IMO should not be used.

Post 29 Dec 2011, 13:52
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Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8346
Location: Kraków, Poland
Tomasz Grysztar 29 Dec 2011, 14:35
fasm doesn't have any warning system, its directives are quite low-level, a building blocks which can be used to do many different things. So if only assembling the given composition of those pieces is possible, it is correct -simple as that. Warnings may discourage use of fasm's features in a way that was not predicted earlier, thus I do not plan to have any in the fasm's core. However you can have warnings implemented in some high-level macros, like "struct", which would be designed to be used strictly for one purpose, so it would be good to discourage any non-standard usage in their case.
Post 29 Dec 2011, 14:35
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