# SysABI

Syscalls are a way for programms to communicate with the kernel.

To perform a syscall, you need to populate the following registers:

| Register | Value           |
|----------|-----------------|
| rax      | The syscalls ID |
| rdi      | Argument 1      |
| rsi      | Argument 2      |
| rdx      | Argument 3      |
| rcx      | Argument 4      |

---

The following calls should be implemented to some degree in noxos 1.0.

# Categories
## Files
| ID     | Name         | Description                                                                                                                                                                                                                                      | Arg1 | Arg2   | Arg3 | Arg4        | Result | Status      | 
|--------|--------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------|--------|------|-------------|--------|-------------|
| 0x0101 | `nx_fopen`   | Opens the file at the _len_ bytes long path _path_ and writes a file descriptor to the referenced file into _fd_ (which needs to be a pointer).                                                                                                  | path | len    | *fd  |             | status | Implemented |
| 0x0102 | `nx_fclose`  | Closes the file which is indicated by descriptor _fd_. This should always be called, otherwise the OS will have to unload files without knowledge of usage.                                                                                      | fd   |        |      |             | status | Implemented |
| 0x0103 | `nx_fread`   | Reads at most _n_ bytes from a file given as descriptor _fd_ and at a specific position _offset_ into a given memory region _mem_.                                                                                                               | fd   | offset | mem  | n           | status | Implemented |
| 0x0104 | `nx_fwrite`  | Writes _n_ bytes from a given memory region _mem_ into the file referenced by _fd_ at the given position _offset_, not inserting but either overwriting existing content or appending to the file.                                               | fd   | offset | mem  | n           | status | Implemented |
| 0x0105 | `nx_fdelete` | Completely delete the file or folder at a given path _path_, which is _len_ bytes long.                                                                                                                                                          | path | len    |      |             | status | Implemented |
| 0x0106 | `nx_flist`   | List all files and/or directories at the _len_ bytes long path _path_ and write their NULL-separated names into _mem_. When _mem_ is NULL, _needed_mem_ (which needs to be a pointer to an 32-bit integer) is filled with the appropriate value. | path | len    | mem  | *needed_mem | status | Implemented |
| 0x0107 | `nx_finfo`   | Writes the information about the files attribute _attr_ into mem. Types of attributes are described below.                                                                                                                                       | fd   | attr   | mem  |             | status | N/A         |

**Note:** The _len_ argument of paths isn't used at the moment, rather than using _len_, _path_ needs to be Null-Terminated.

## Memory
| ID     | Name        | Description                                                                                                                                     | Arg1 | Arg2 | Arg3  | Arg4 | Result | Status      | 
|--------|-------------|-------------------------------------------------------------------------------------------------------------------------------------------------|------|------|-------|------|--------|-------------|
| 0x0201 | `nx_mmap`   | Maps _n_ 4KB pages to address _addr_. You can provide a bitmap of flags with the _flags_ argument. Which flags can be used, is described below. | addr | n    | flags |      | status | Implemented |
| 0x0202 | `nx_munmap` | Unmaps _n_ 4KB pages at address _addr_.                                                                                                         | addr | n    |       |      | status | Implemented |

## Processes
| ID  | Name | Description | Arg1 | Arg2 | Arg3 | Arg4 | Result | Status | 
|-----|------|-------------|------|------|------|------|--------|--------|
|     |      |             |      |      |      |      |        |        |

## Runtime / Dynamic Linker
| ID  | Name | Description | Arg1 | Arg2 | Arg3 | Arg4 | Result | Status | 
|-----|------|-------------|------|------|------|------|--------|--------|
|     |      |             |      |      |      |      |        |        |

## Compatibility & Safety
| ID  | Name | Description | Arg1 | Arg2 | Arg3 | Arg4 | Result | Status | 
|-----|------|-------------|------|------|------|------|--------|--------|
|     |      |             |      |      |      |      |        |        |

## Kernel
The kernel syscalls can only be called from the kernels main process [link to processing article needed].
If another process calls them, they will just return without doing anything.


| ID  | Name | Description | Arg1 | Arg2 | Arg3 | Arg4 | Result | Status |
|-----|------|-------------|------|------|------|------|--------|--------|
|     |      |             |      |      |      |      |        |        |

---

## Appendixes

### Types of file attributes

| ID  | Name          | Description                                | Data Type | Status |
|-----|---------------|--------------------------------------------|-----------|--------|
| 0   | `permissions` | Who has what permission to access the file | uint16_t  | N/A    |
| 1   | `size`        | The files size in bytes                    | uint64_t  | N/A    |


### Memory mapping flags

| Bit | Name      | Description                               |
|-----|-----------|-------------------------------------------|
| 0   | `write`   | Enables write access to the mapped pages. |
| 1   | `no_exec` | Prevents execution of the mapped pages.   |