Simple puts() function in x64 assembly

up vote
2
down vote

favorite

I'm trying to write as simple I/O library in x64 using linux syscalls

section .text
strlen:
 xor rdx, rdx
 .loop:
 cmp [rsi + rdx], 0
 je .exit
 inc rdx
 jmp .loop
 .exit:
 ret ; value in rdx

puts:
 ; string passed through rsi
 mov rax, 1 ; WRITE syscall
 mov rdi, 1 ; fd for stdout
 call strlen
 syscall

edited 16 mins ago

asked 4 hours ago

Meme myself and a very creepy

514

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up vote
2
down vote

favorite

I'm trying to write as simple I/O library in x64 using linux syscalls

section .text
strlen:
 xor rdx, rdx
 .loop:
 cmp [rsi + rdx], 0
 je .exit
 inc rdx
 jmp .loop
 .exit:
 ret ; value in rdx

puts:
 ; string passed through rsi
 mov rax, 1 ; WRITE syscall
 mov rdi, 1 ; fd for stdout
 call strlen
 syscall

edited 16 mins ago

asked 4 hours ago

Meme myself and a very creepy

514

add a commentÂ |Â

up vote
2
down vote

favorite

I'm trying to write as simple I/O library in x64 using linux syscalls

section .text
strlen:
 xor rdx, rdx
 .loop:
 cmp [rsi + rdx], 0
 je .exit
 inc rdx
 jmp .loop
 .exit:
 ret ; value in rdx

puts:
 ; string passed through rsi
 mov rax, 1 ; WRITE syscall
 mov rdi, 1 ; fd for stdout
 call strlen
 syscall

edited 16 mins ago

asked 4 hours ago

Meme myself and a very creepy

514

I'm trying to write as simple I/O library in x64 using linux syscalls

section .text
strlen:
 xor rdx, rdx
 .loop:
 cmp [rsi + rdx], 0
 je .exit
 inc rdx
 jmp .loop
 .exit:
 ret ; value in rdx

puts:
 ; string passed through rsi
 mov rax, 1 ; WRITE syscall
 mov rdi, 1 ; fd for stdout
 call strlen
 syscall

strings io linux assembly x86

edited 16 mins ago

asked 4 hours ago

Meme myself and a very creepy

514

edited 16 mins ago

asked 4 hours ago

Meme myself and a very creepy

514

edited 16 mins ago

asked 4 hours ago

Meme myself and a very creepy

514

asked 4 hours ago

Meme myself and a very creepy

514

asked 4 hours ago

Meme myself and a very creepy

514

add a commentÂ |Â

1 Answer
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up vote
2
down vote

Your loop uses 2 jumps (je/jmp) on every iteration! Jumping is expensive, so a solution that needs only 1 jump (jne) will be more effective.

strlen:
 xor rdx, rdx
 dec rdx ; This compensates for the INC that is happening first.
.next:
 inc rdx
 cmp byte [rsi + rdx], 0
 jne .next
 ret

Do keep things logically together. There's no point in setting RAX before the call to strlen.

puts:
 ; string passed through rsi
 call strlen ; Result is in RDX

 mov rax, 1
 syscall

answered 3 hours ago

Fifoernik

30027

Would it be best to make an generalization of this and cal it fputs then have puts just mov rdi, 1 and call puts?
â€“Â Meme myself and a very creepy
19 mins ago

add a commentÂ |Â

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1 Answer
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active

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1 Answer
1

active

oldest

votes

up vote
2
down vote

Your loop uses 2 jumps (je/jmp) on every iteration! Jumping is expensive, so a solution that needs only 1 jump (jne) will be more effective.

strlen:
 xor rdx, rdx
 dec rdx ; This compensates for the INC that is happening first.
.next:
 inc rdx
 cmp byte [rsi + rdx], 0
 jne .next
 ret

Do keep things logically together. There's no point in setting RAX before the call to strlen.

puts:
 ; string passed through rsi
 call strlen ; Result is in RDX

 mov rax, 1
 syscall

answered 3 hours ago

Fifoernik

30027

Would it be best to make an generalization of this and cal it fputs then have puts just mov rdi, 1 and call puts?
â€“Â Meme myself and a very creepy
19 mins ago

add a commentÂ |Â

up vote
2
down vote

Your loop uses 2 jumps (je/jmp) on every iteration! Jumping is expensive, so a solution that needs only 1 jump (jne) will be more effective.

strlen:
 xor rdx, rdx
 dec rdx ; This compensates for the INC that is happening first.
.next:
 inc rdx
 cmp byte [rsi + rdx], 0
 jne .next
 ret

Do keep things logically together. There's no point in setting RAX before the call to strlen.

puts:
 ; string passed through rsi
 call strlen ; Result is in RDX

 mov rax, 1
 syscall

answered 3 hours ago

Fifoernik

30027

Would it be best to make an generalization of this and cal it fputs then have puts just mov rdi, 1 and call puts?
â€“Â Meme myself and a very creepy
19 mins ago

add a commentÂ |Â

up vote
2
down vote

Your loop uses 2 jumps (je/jmp) on every iteration! Jumping is expensive, so a solution that needs only 1 jump (jne) will be more effective.

strlen:
 xor rdx, rdx
 dec rdx ; This compensates for the INC that is happening first.
.next:
 inc rdx
 cmp byte [rsi + rdx], 0
 jne .next
 ret

Do keep things logically together. There's no point in setting RAX before the call to strlen.

puts:
 ; string passed through rsi
 call strlen ; Result is in RDX

 mov rax, 1
 syscall

answered 3 hours ago

Fifoernik

30027

Your loop uses 2 jumps (je/jmp) on every iteration! Jumping is expensive, so a solution that needs only 1 jump (jne) will be more effective.

strlen:
 xor rdx, rdx
 dec rdx ; This compensates for the INC that is happening first.
.next:
 inc rdx
 cmp byte [rsi + rdx], 0
 jne .next
 ret

Do keep things logically together. There's no point in setting RAX before the call to strlen.

puts:
 ; string passed through rsi
 call strlen ; Result is in RDX

 mov rax, 1
 syscall

answered 3 hours ago

Fifoernik

30027

answered 3 hours ago

Fifoernik

30027

answered 3 hours ago

Fifoernik

30027

answered 3 hours ago

Fifoernik

30027

Would it be best to make an generalization of this and cal it fputs then have puts just mov rdi, 1 and call puts?
â€“Â Meme myself and a very creepy
19 mins ago

add a commentÂ |Â

Would it be best to make an generalization of this and cal it fputs then have puts just mov rdi, 1 and call puts?
â€“Â Meme myself and a very creepy
19 mins ago

Would it be best to make an generalization of this and cal it fputs then have puts just mov rdi, 1 and call puts?
â€“Â Meme myself and a very creepy
19 mins ago

add a commentÂ |Â

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