CODEWITHSUNDEEP
linuxgccnasmelfsystem-calls
jiamo
jiamo

Reputation: 1456

syscall return 07 when call _exit

I am looking a paper Size Is EverythingSize Is Everything with kernel 3.8.4 x64 nasm gcc-4.7.2 fedora

by type in moretiny.asm 

BITS 64

EXTERN _exit
GLOBAL _start
SECTION .text

_start:
    push dword 42
    call  _exit

\>nasm -f elf64 moretiny.asm 
\>gcc -Wall -s -nostartfiles -o moretiny.
\>./a.out ; echo $?

7

With gdb help . break at _exit

(gdb) display /i $pc
1: x/i $pc
=> 0x3a5e0bb750 <_exit>:    movslq %edi,%rdx
(gdb) si
0x0000003a5e0bb753 in _exit () from /lib64/libc.so.6
1: x/i $pc
=> 0x3a5e0bb753 <_exit+3>:  mov    0x2f56de(%rip),%r10        # 0x3a5e3b0e38
(gdb) 
0x0000003a5e0bb75a in _exit () from /lib64/libc.so.6
1: x/i $pc
=> 0x3a5e0bb75a <_exit+10>: mov    $0xe7,%r9d
(gdb) 
0x0000003a5e0bb760 in _exit () from /lib64/libc.so.6
1: x/i $pc
=> 0x3a5e0bb760 <_exit+16>: mov    $0x3c,%r8d
(gdb) 
0x0000003a5e0bb766 in _exit () from /lib64/libc.so.6
1: x/i $pc
=> 0x3a5e0bb766 <_exit+22>: jmp    0x3a5e0bb781 <_exit+49>
(gdb) 
0x0000003a5e0bb781 in _exit () from /lib64/libc.so.6
1: x/i $pc
=> 0x3a5e0bb781 <_exit+49>: mov    %rdx,%rdi
(gdb) 
0x0000003a5e0bb784 in _exit () from /lib64/libc.so.6
1: x/i $pc
=> 0x3a5e0bb784 <_exit+52>: mov    %r9d,%eax
(gdb) 
0x0000003a5e0bb787 in _exit () from /lib64/libc.so.6
1: x/i $pc
=> 0x3a5e0bb787 <_exit+55>: syscall 
(gdb) 
[Inferior 1 (process 32082) exited with code 07]

seem like the syscall return the code with 07 , I am not sure why .

Upvotes: 2

Views: 190

Answers (1)

Anya Shenanigans
Anya Shenanigans

Reputation: 94729

The x86_64 abi specifies the parameter passing convention.

In this case:

If the class is INTEGER, the next available register of the sequence %rdi, %rsi, %rdx, %rcx, %r8 and %r9 is used12 .

so you should use the %rdi register instead of pushing onto the stack.

This is quite evident from your single-step debugging into the _exit function call.

Upvotes: 3

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