Anyway to check defines after they've been declared?

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sid123

Joined: 30 Jul 2013
Posts: 338
Location: Asia, Singapore

sid123 09 Jul 2014, 09:20

Hi,
I'm writing a VM which uses my own executable format. It uses fasm as the assembler and all instructions are done through macros. What I want is to check for the stack size given by the programmer, and if it's not defined then fall back to default.
My programs look like this:

Code:

include 'cpu.inc'
DEFINE STACK_SIZE 200
..code....

"cpu.inc" contains the header for the programs and a few macros that define CPU instructions.
Basically I want to check if STACK_SIZE was defined by the programmer anywhere in the source code and then set the "stack_buf" entry manually in the header.
Something like:

Code:

ifdef STACK_BUF
dd _end_bss + STACK_BUF
else 
; Fall back to default stack size
dd _end_bss + 200
endif

Cheers,
sid123

_________________
"Those who can make you believe in absurdities can make you commit atrocities" -- Voltaire https://github.com/Benderx2/R3X
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09 Jul 2014, 09:20

JohnFound

Joined: 16 Jun 2003
Posts: 3499
Location: Bulgaria

JohnFound 09 Jul 2014, 10:54

Use assembling stage constants instead of preprocessor one:

Code:

STACK_SIZE = 200

Then use:

Code:

if defined STACK_SIZE

09 Jul 2014, 10:54

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8466
Location: Kraków, Poland

Tomasz Grysztar 09 Jul 2014, 11:54

You should follow JohnFound's suggestion, because for anything that is numeric and needs to be forward-referenced you should use the assembly-time variables.

But I'd like to show a little trick that demonstrates how to use some of the newest fasm's features to make it work with your "DEFINE STACK_SIZE" sources:

Code:

postpone { local S
           irpv s,STACK_SIZE \{ S = s \}
           if defined S
             STACK_BUF = S
           end if }

if defined STACK_BUF
  dd _end_bss + STACK_BUF
else
  ; Fall back to default stack size
  dd _end_bss + 200
end if

This code defines the global STACK_BUF label with the last value of STACK_SIZE symbolic variable (in case when there was more than one DEFINE). STACK_BUF, as opposed to STACK_SIZE, is assembly-time variable and can be used with "if defined".

09 Jul 2014, 11:54

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