https://github.com/barimehdi77/libasm
The aim of this project is to get familiar with assembly language.
https://github.com/barimehdi77/libasm
Last synced: 7 months ago
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The aim of this project is to get familiar with assembly language.
- Host: GitHub
- URL: https://github.com/barimehdi77/libasm
- Owner: barimehdi77
- Created: 2020-12-15T13:08:12.000Z (almost 5 years ago)
- Default Branch: main
- Last Pushed: 2021-06-01T17:36:15.000Z (over 4 years ago)
- Last Synced: 2025-02-02T01:13:49.418Z (8 months ago)
- Language: C
- Size: 24.4 KB
- Stars: 2
- Watchers: 2
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
# 🧰 libasm
The aim of this project is to get familiar with assembly language.
# 🤔 Description:
Write the following functions in x64 assembly (in the Intel syntax):
```C
int ft_strlen(char const *str);
int ft_strcmp(char const *s1, char const *s2);
char *ft_strcpy(char *dst, char const *src);
ssize_t ft_write(int fd, void const *buf, size_t nbyte);
ssize_t ft_read(int fd, void *buf, size_t nbyte);
char *ft_strdup(char const *s1);
```
# 📟 Registers
```
; 64-bit [QWORD]
R0 R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 R14 R15
RAX RCX RDX RBX RSP RBP RSI RDI
; 32-bit [DWORD]
R0D R1D R2D R3D R4D R5D R6D R7D R8D R9D R10D R11D R12D R13D R14D R15D
EAX ECX EDX EBX ESP EBP ESI EDI
; 16-bit [WORD]
R0W R1W R2W R3W R4W R5W R6W R7W R8W R9W R10W R11W R12W R13W R14W R15W
AX CX DX BX SP BP SI DI
; 8-bit [BYTE]
R0B R1B R2B R3B R4B R5B R6B R7B R8B R9B R10B R11B R12B R13B R14B R15B
AL CL DL BL SPL BPL SIL DIL
; 128-bit (used for floating point operations mostly)
XMM0 ... XMM15
```
# 🔑 Common
```
; Save register
push REG
pop REG
; Set register value
mov REG, VALUE ; DEST = VALUE
; Common operations
add DEST, VALUE ; DEST = DEST + VALUE
sub - ; DEST = DEST - VALUE
inc REG ; REG++
dec - ; REG--
and DEST, REG ; DEST = DEST & REG
xor - ; DEST = DEST ^ REG
xor REG, REG ; = mov REG, 0
mul REG ; REG = REG * RAX
div REG ; REG = REG / RAX
; Dereferenced value
[REG] ; = *REG
; Compare
cmp REG, VALUE ; Set flags used by jmp variants
; Label
label:
jmp label ; next jumps depends on compare flags from cmp
je - ; is equal
jne - ; is not equal
jl - ; < VALUE
jle - ; <= VALUE
jz - ; = 0
jnz - ; != 0
jg - ; > VALUE
jge - ; >= VALUE
```
# 🕹 Functions
```
; Function call
call FUNCTION
; Parameters registers
RDI RSI RDX RCX R8 R9
; Register to preserve
RBP RBX R12 R13 R14 R15 ; You **MUST** push/pop them if you use them
; Return register
RAX
; syscall
mov rax, CODE ; Then RDI, RSI etc.. for params
; Add 0x2000000 to the syscall number, see table below
syscall
```
# 👨💻 Ressources
* [syscalls MacOS](https://opensource.apple.com/source/xnu/xnu-1504.3.12/bsd/kern/syscalls.master)
* [Linux syscalls](https://blog.rchapman.org/posts/Linux_System_Call_Table_for_x86_64/)
* [Hello, world!](https://gist.github.com/FiloSottile/7125822)
* [NASM Tutorial](https://cs.lmu.edu/~ray/notes/nasmtutorial/)
* [Stack Alignment](https://forum.nasm.us/index.php?topic=1689.0)