How to print a string in assembly intel x86 without changing the data-CodePudding

I have this piece:

.global main

.data
helloworld: .ascii "Hello world\n"
helloworldend:
goodluck: .asciz "Good Luck!\n"
goodluckend:

.text
main:
    # printf(helloworld)
    movq $1, %rax
    movq $1, %rdi
    movq $helloworld, %rsi
    movq $helloworldend-helloworld, %rdx
    syscall

    # printf(goodluck)
    movq $1, %rax
    movq $1, %rdi
    movq $goodluck, %rsi
    movq $goodluckend-goodluck, %rdx
    syscall

    xorq %rax, %rax
    ret

And I have to somehow make it also print "Hello Luck" without changing the data section. What I did is add a new data section inside the main:

...
main:
   
.section .data
msg: .ascii "Hello Luck\n"
msgend:

.section .text
start:
    movq $1, %rax
    movq $1, %rdi
    movq $msg, %rsi
    movq $msgend-msg, %rdx
    syscall
...

And obviously that works but I'm not sure that that was the idea.. Is there a different way of printing it without adding a new data section and without changing the existing one?

CodePudding user response：

Kernel syscall sys_write expects RDX=number of bytes and RSI=pointer to the string, which doesn't have to be null-terminated, so just change those two registers:

main:
    # printf("Hello ")
    movq $1, %rax
    movq $1, %rdi
    movq $helloworld, %rsi ; Pointer to "Hello World\n".
    movq $6, %rdx          ; Size of "Hello ".
    syscall

    # printf("Luck\n")
    movq $1, %rax
    movq $goodluck   5, %rsi ; Pointer to "Luck\n".
    movq $5, %rdx             ; Size of "Luck\n".  
    syscall

    xorq %rax, %rax
    ret