ld --dynamic-linker /lib/ld-linux.so.2 -o [name] -lc [name].o
When we apply it we have “Accessing a corrupted shared library”. I am using Linux Mint 13, based on Ubuntu 12.04, and /lib/ld-linux.so.2 is symlink to 32 bit library:
$ ls -l /lib/ld-linux.so.2
lrwxrwxrwx 1 root root 25 Sep 30 16:38 /lib/ld-linux.so.2 -> i386-linux-gnu/ld-2.15.so
Since we are on 64 bit architecture we need to modify linking to use appropriate architecture:
ld --dynamic-linker /lib/x86_64-linux-gnu/ld-linux-x86-64.so.2 -o [name] -lc [name].o
That should eliminate “Accessing a corrupted shared library” problem. Now we have calling printf problem. On 32 bit architecture we simply push on the stack parameters and on 64 bit machine that just doesn’t work. Calling convention for 64 bit architecture is the following: result will end up in %rax, parameters, in order of appearance, will go into %rdi, %rsi, %rdx, %rcx and so on. There is quite good article about it GNU x86_64 assembler - Calling printf by Aleksandar Mitrevski. Now we can try some Hello World examples.
.section .data
hws:
.asciz "Hello World!\n"
.section .text
.globl _start
_start:
mov $hws, %rdi
call printf
call exit
We place our zero terminated string into register %rdi and call printf. To compile, link and execute we execute the following from terminal:
$ as -o helloworld.o helloworld.s
$ ld --dynamic-linker /lib/x86_64-linux-gnu/ld-linux-x86-64.so.2 -o helloworld -lc helloworld.o
$ ./helloworld
Now slightly more complicated example:
.section .data
whatever:
.int 1234
format:
.asciz "Our integer is %d\n"
.section .text
.globl _start
_start:
movq whatever, %rsi
movq $format, %rdi
movq $0, %rax
call printf
movl $1, %eax
movl $0, %ebx
int $0x80
The last three lines can be replaced with call exit, but this is more like examples from book Professional assembly language by Richard Blum. Final example with even more parameters and some addition:
.section .data
a:
.int 1234
b:
.int 766
format:
.asciz "%d + %d = %d\n"
.section .text
.globl _start
_start:
movq a, %rsi
movq b, %rdx
movq $format, %rdi
movq %rsi, %rcx
addq %rdx, %rcx
movq $0, %rax
call printf
call exit
If you managed to build and execute all three examples, quickly go and update your CV with freshly acquired assembly on Linux experience.
