fasm as DLL

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masm

Joined: 10 Oct 2014
Posts: 6

masm 12 Aug 2019, 17:30

please helps how i can compile FASMX64.ASM ? when i complile with last version 1.73.16 it is give me erros.

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12 Aug 2019, 17:30

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8359
Location: Kraków, Poland

Tomasz Grysztar 12 Aug 2019, 19:41

I'm not sure what might have caused this problem in your case, but I have updated the fasmDLL.zip with re-assembled 1.73.16 version. Please check if the new one works for you.

12 Aug 2019, 19:41

DimonSoft

Joined: 03 Mar 2010
Posts: 1228
Location: Belarus

DimonSoft 12 Aug 2019, 21:13

My first guess was that you’re trying to compile PREPROCE.INC only (start from this file) which doesn’t contain the symbol. Looked through the file and checked that. Choose FASMX64.ASM tab before compiling or better assign it to compiler from context menu.

12 Aug 2019, 21:13

Abruzzi

Joined: 30 Sep 2019
Posts: 17

Abruzzi 09 Jan 2020, 16:02

I used FASM DLL to assembly a simple instruction like xor eax, eax and I wonder why the output_length for this particular instruction is 3 and output binary data is something like 0x6631C0.

I tried to add one more instruction to see how the output is changing and for these two lines

Code:

xor eax, eax
xor eax, eax

the output_length is 6 and output binary data is 0x6631C06631C0. What is this extra byte (0x66) used for?

09 Jan 2020, 16:02

ProMiNick

Joined: 24 Mar 2012
Posts: 805
Location: Russian Federation, Sochi

ProMiNick 09 Jan 2020, 16:48

try this sequence

Code:

use16
xor eax, eax

thou will see output is the same as thours
than try

Code:

use32
xor eax, eax

use16 mode is by default in fasm
thou could play with these samples too

Code:

use16
xor ax, ax

Code:

use32
xor ax, ax

Abruzzi, than I congratulate thou - thou explore bicicle.

09 Jan 2020, 16:48

Abruzzi

Joined: 30 Sep 2019
Posts: 17

Abruzzi 09 Jan 2020, 17:16

Many thanks ProMiNick. Indeed using use32 directive the output is 2 bytes length and the resulted opcode is 0x31C0 as I expect.

I tried your examples also.

Code:

use16
xor ax, ax

generates 0x31C0 as 32 bit mode if I use eax register and

Code:

use32
xor ax, ax

generates 0x6631C0 as 16 bit mode if I use eax register

I have to dig out to understand why it's encoded in that way. Right now it's just witchcraft. Shocked

09 Jan 2020, 17:16

ProMiNick

Joined: 24 Mar 2012
Posts: 805
Location: Russian Federation, Sochi

ProMiNick 09 Jan 2020, 17:33

try to dig out at https://www.youtube.com/channel/UCs_OWSjmFntZqjzSpgJoBhA/featured in decoding instructions

09 Jan 2020, 17:33

Abruzzi

Joined: 30 Sep 2019
Posts: 17

Abruzzi 09 Jan 2020, 18:10

It makes sense now why 66h prefix appear before instruction opcode when I am using 32 bit mode and 16 bit operands and vice versa as I could see. Thank you again ProMiNick.

09 Jan 2020, 18:10

soloworker

Joined: 09 Dec 2020
Posts: 9

soloworker 09 Dec 2020, 01:24

How can we use this assembler to get the relocatable offsets?

Code:

mov eax,401000h ;Offset
push eax

It would be great if it supports the read of these types like for example

"Offsets" it writes back the indexes to the offsets. Same for .data section.

Any idea how to achieve that?

09 Dec 2020, 01:24

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20454
Location: In your JS exploiting you and your system

revolution 09 Dec 2020, 05:08

If you use PE format and include a relocs table then you will get a fully relocatable exe.

09 Dec 2020, 05:08

soloworker

Joined: 09 Dec 2020
Posts: 9

soloworker 25 Dec 2020, 02:31

Thx revolution. I have noticed that unrefrenced code is not compiled. Why is this case?

25 Dec 2020, 02:31

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20454
Location: In your JS exploiting you and your system

revolution 25 Dec 2020, 03:15

If you use the normal fasm proc/endp macros then it has lines like this:

Code:

if used function ; in proc macro
;...
end if ; in endp macro

25 Dec 2020, 03:15

soloworker

Joined: 09 Dec 2020
Posts: 9

soloworker 25 Dec 2020, 03:46

revolution wrote:

If you use the normal fasm proc/endp macros then it has lines like this:
Code:
if used function ; in proc macro
;...
end if ; in endp macro    

You mean the define@proc macro?

Quote:

macro define@proc name,statement
{ local params,flag,regs,parmbytes,localbytes,current
if used name

Ok i found it. Thanks for your help.

25 Dec 2020, 03:46

soloworker

Joined: 09 Dec 2020
Posts: 9

soloworker 01 Jan 2021, 08:34

I have a question
Does fasm allocate memory for the same data used in source?
Like for example:

Code:

section '.data' data readable writeable
something  db 83886080 dup(?) '80MB

When assembling, the fasm.exe memory usage goes over 90 MB. Why is this?

01 Jan 2021, 08:34

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20454
Location: In your JS exploiting you and your system

revolution 01 Jan 2021, 08:37

fasm allocates all data and code in RAM. That includes all uninitialised values.

01 Jan 2021, 08:37

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8359
Location: Kraków, Poland

Tomasz Grysztar 01 Jan 2021, 11:48

soloworker wrote:

I have a question
Does fasm allocate memory for the same data used in source?
Like for example:
Code:
section '.data' data readable writeable
something  db 83886080 dup(?) '80MB     
When assembling, the fasm.exe memory usage goes over 90 MB. Why is this?

The way fasm handles uninitialized data definitions is very similar to initialized ones, it only cuts them out afterwards when possible.

This was improved in case of fasmg's engine - if you assemble the same thing with fasmg, that uninitialized definition is not going to cause any additional memory usage unless you force it to become initialized by putting something initialized after it in the same section.

01 Jan 2021, 11:48

soloworker

Joined: 09 Dec 2020
Posts: 9

soloworker 07 Mar 2021, 05:04

Tomasz Grysztar wrote:

soloworker wrote:
I have a question
Does fasm allocate memory for the same data used in source?
Like for example:
Code:
section '.data' data readable writeable
something  db 83886080 dup(?) '80MB     
When assembling, the fasm.exe memory usage goes over 90 MB. Why is this?
The way fasm handles uninitialized data definitions is very similar to initialized ones, it only cuts them out afterwards when possible.

This was improved in case of fasmg's engine - if you assemble the same thing with fasmg, that uninitialized definition is not going to cause any additional memory usage unless you force it to become initialized by putting something initialized after it in the same section.

Thanks for the tip.
I still don't understand why it uses huge memory (like 400mb) when compiling some relatively small exe under 2mb of size with only this code as data. But the size of the code of (.asm) file is 7mb. So big code with few data will also have this problem.

Code:

section '.data' data readable writeable
sss db 'AXaaaaaaaaaaaaAXaaaaaaaaaaaaAXaaaaaaaaaaaaAXaaaaaaaaaaaa',0
sss2 db 'atatatatatatatatatatatatatatatatatatatatat',0
sss3 db 'tatatatatatatatatatatatatatatatatata',0
sss4 db '53535535355353553535535355353553535535355353553535535355353553535535355353553535535355353553535',0

07 Mar 2021, 05:04

soloworker

Joined: 09 Dec 2020
Posts: 9

soloworker 09 Mar 2021, 23:42

I found why it uses huge memory.
The macro that is responsible for this is

Code:

allow_nesting

in WIN32AX.inc file.

If i remove it, fasm.exe uses way less memory. What does it do?

09 Mar 2021, 23:42

bitRAKE

Joined: 21 Jul 2003
Posts: 4075
Location: vpcmpistri

bitRAKE 10 Mar 2021, 03:16

iirc, allow_nesting enables using invoke as parameter to another invoke.

Code:

invoke CommandLineToArgvW, <invoke GetCommandlineW>,ADDR nargs

etc.

_________________
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10 Mar 2021, 03:16

Ben321

Joined: 07 Dec 2017
Posts: 70

Ben321 06 Dec 2023, 11:44

Tomasz Grysztar wrote:

The subject says all.

I've made fasm into a simple DLL which allows to assemble just inside the memory. The package contains short documentation, demonstration program (which also uses flat editor in DLL form) and the SOURCE directory, which needs to be merged with SOURCE directory of standard fasm's distributions.

I found a bug in the FASM DLL. Not sure if this also impacts the normal EXE version, but I found it certainly impacts the DLL version.

To tell it that a number is hexadecimal, you can either prepend "0x" or append "h" to the number. I found this doesn't work though if the first digit of the number is a hexadecimal letter. For example, 0xF00000 works, but F00000h generates an error. It's fine if the letter is elsewhere in the hex number. This means a temporary work around hers is to prepend a zero before the first letter, like 0F00000h will work. But it's not ideal. I hope this is a bug that you can fix.

06 Dec 2023, 11:44

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