stack-problem with amd64

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Spinne

Joined: 17 Apr 2006
Posts: 2
Location: Germany

Spinne 17 Apr 2006, 10:32

Hello.
When I wrote 32-bit programs, it was no problem to print characters from the stack on the screen. I simply pushed the characters and called sys_write with ecx=esp (the address of the characters) ... and it worked.
But now I'm trying to do so in a 64-bit programm. But unfortunately it doesn't work. Here is a simple code for demonstrating my problem:

Code:

format ELF64 executable
segment writeable readable executable
entry $
 mov rax,0x4141414141414141 ; 'AAAAAAAA'
 push rax
 mov rax,4
 mov rbx,1
 mov rcx,rsp
 mov rdx,1
 int 0x80
 pop rax

 mov rax,1
 int 0x80

The same program in 32-bit worked fine, but nothing happens now. I hope you can help me seeing my mistake.

17 Apr 2006, 10:32

Endre

Joined: 29 Dec 2003
Posts: 215
Location: Budapest, Hungary

Endre 20 Apr 2006, 09:13

1. If you have 32bit kernel then you have to use the legacy 32 bit system calls across int 0x80 and 32bit registers.
2. If you have 64bit kernel then you have to use the new system call technique which is no longer based on int 0x80 but on instructions syscall, sysret. This means that system calls are no longer interrupt but call-gates.

20 Apr 2006, 09:13

Spinne

Joined: 17 Apr 2006
Posts: 2
Location: Germany

Spinne 01 May 2006, 11:26

Yes, I'm using a 64bit kernel. And with syscall it works. Thank you.

01 May 2006, 11:26

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