x86_64 assembly execve *char[] syscall

Question

I am trying to get into a bit of Linux 64bit x86 assembly without using the standard libs, however I am having some issues dealing with arguments presented to my program (argv). I would think (based on documentation) that rsp marks the beginning of the argc qword, whilst [rsp + 8] would be argv. Unfortunately this is not the case, and the following (abridged) program causes EFAULT (Bad address).

sys_execve equ 59
sys_exit equ 60

section .data
    child db "/bin/sh", 0

global _start

section .text
    _start:
        mov rdi, child      ; #1 filename
        mov rsi, [rsp + 8]      ; #2 argv
        mov rdx, 0      ; #3 envp = 0

        mov rax, sys_execve ; execve
        syscall
        mov rax, rdi        ; #1 Return value
        mov rax, sys_exit   ; exit
        syscall

Help with regards to the amd64 calling convention and passing *char[] into the kernel would be appreciated.

Thanks

Answer 1

At rsp+8 you'll find the address of a string with the program path. The pointer to the first argument is at [rsp+16]. But for execve you need a pointer to an array of pointer to strings which begins with a pointer to a program path (you can (ab)use [rsp+8]).

So change

mov rsi, [rsp + 8]

to

lea rsi, [rsp + 8]