[SOLVED] Question: Getting environment variables

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n0tmuch

Joined: 10 Oct 2025
Posts: 2

n0tmuch 10 Oct 2025, 19:38

Hello! This may sound a bit dumb as the solution is probably simple, but how do I get the environment variables for my program? The flat assembler.'s examples doesn't include this right now. Sad

Arch is x86_64.

Last edited by n0tmuch on 10 Oct 2025, 20:32; edited 1 time in total

10 Oct 2025, 19:38

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8461
Location: Kraków, Poland

Tomasz Grysztar 10 Oct 2025, 20:09

You can find an example in fasmg source:

Code:

  start:
        mov     rcx,[rsp]
        mov     [argc],rcx
        lea     rbx,[rsp+8]
        mov     [argv],rbx
        lea     rsi,[rsp+8+rcx*8+8]
        mov     [env],rsi

This pointer is then used by get_environment_variable function in system.inc.

10 Oct 2025, 20:09

n0tmuch

Joined: 10 Oct 2025
Posts: 2

n0tmuch 10 Oct 2025, 20:31

That explains it! The simplified code for anyone else finding this:

Code:

mov rbp, [rsp]
lea rbx, [rsp+8+rbp*8+8]
mov [env], rbx

This could be used for execve and similar, by moving [env] into rdx.

10 Oct 2025, 20:31

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