NASM-Template-MacOS
Adopted from here
This is a template for writing assembly using NASM on Mac OS X.
It has a template "main" file, makefile, and a few helper functions "IO.inc" to help with I/O without having to use syscalls explicitly.
Function Guide:
| Function | Parameters | Returns | Description |
|---|---|---|---|
| ReadChar | N/A | al: Character read | Reads a character from STDIN and saves it in al. |
| WriteChar | al: Character | N/A | Writes the specified ASCII character to STDOUT. |
| ReadString | ecx: String max length esi: Address of storage location | eax: Number of bytes read | Reads a string from STDIN and saves it at the specified address. |
| WriteString | ecx: Length of the string esi: Address of the string | N/A | Writes the specified string to STDOUT. |
| WriteLine | N/A | N/A | Writes a new line ('\n') to STDOUT. |
| WriteDec | eax: Value to be written | N/A | Writes the specified value in base-10 (Decimal) to STDOUT. |
| ReadHexByte | N/A | al: Value read | Reads a hex byte from STDIN, without 0x or h. Ex: 3A or F5 |
| WriteHex | eax: Value to be written | N/A | Writes the specified hex value to STDOUT. |
| Print4x4Matrix | esi: byte array of length 16 | N/A | Write the array as a 4x4 hex grid. |
Usage
- Install nasm with
brew install nasm - Write assembly in program.asm
- Compile project with
make - Run
./program
Syscalls
On MacOS, syscalls work slightly differently. If you want to invoke a syscall, you have to OR the syscall id placed in rax with i<<24 where i is a number from 0 to 4 denoting the syscall class. For example, for UNIX write syscall, put 0x02000004 into rax. The identifiers placed in rax for each syscall are also slightly different. For a list of them, refer here.