I have a code in C which simply prints hello world, like this
#include <stdio.h>
int main(void)
{
printf("Hello, world\n");
}
to compile the code in ubuntu I used the command
make filename
which gives me an assembly code like this:
.text
.file "hello.c"
.globl main
.align 16, 0x90
.type main,@function
main: # @main
.cfi_startproc
# BB#0:
pushq %rbp
.Ltmp0:
.cfi_def_cfa_offset 16
.Ltmp1:
.cfi_offset %rbp, -16
movq %rsp, %rbp
.Ltmp2:
.cfi_def_cfa_register %rbp
subq $16, %rsp
movabsq $.L.str, %rdi
movb $0, %al
callq printf
xorl %ecx, %ecx
movl %eax, -4(%rbp) # 4-byte Spill
movl %ecx, %eax
addq $16, %rsp
popq %rbp
retq
.Lfunc_end0:
.size main, .Lfunc_end0-main
.cfi_endproc
.type .L.str,@object # @.str
.section .rodata.str1.1,"aMS",@progbits,1
.L.str:
.asciz "Hello, world\n"
.size .L.str, 14
.ident "clang version 3.8.0-2ubuntu4 (tags/RELEASE_380/final)"
.section ".note.GNU-stack","",@progbits
Which I then translated into machine language using xxd -b hello
, which gives me (subset of the output)
00000006: 00001010 00001001 00101110 01100110 01101001 01101100 ...fil
0000000c: 01100101 00001001 00100010 01101000 01100101 01101100 e."hel
00000012: 01101100 01101111 00101110 01100011 00100010 00001010 lo.c".
00000018: 00001001 00101110 01100111 01101100 01101111 01100010 ..glob
0000001e: 01101100 00001001 01101101 01100001 01101001 01101110 l.main
00000024: 00001010 00001001 00101110 01100001 01101100 01101001 ...ali
0000002a: 01100111 01101110 00001001 00110001 00110110 00101100 gn.16,
My Question is: Why does the (dot ".") have different representations in binary like in the first and fourth lines we have consecutive dots but with different representations?
I know it's an odd question, but it's only for sake of interest & knowledge, any help would be appreciated
This looks like the dumping tool is representing all non-printable characters by dots.
There are multiple non-printable characters, so there are multiply binary value that are represented by dots.