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Vihaan Jim 2023-08-26 21:58:16 -04:00
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apps/app-loader/spawn/README.md
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# Spawn a process
# Spawn a process & Read an ELF File
This crate represents an initial program that will run when a process
starts up. It will listen on a Server and take orders from the parent
process to finish setting itself up.
## Initialization
The process starts with a stack and a text section but no heap, BSS,
or data section. The entrypoint looks like this:
```rust
pub extern "C" init(a1: u32, a2: u32, a3: u32, a4: u32) -> ! {
let sid = xous::SID::from_u32(a1, a2, a3, a4);
loop {}
}
```
This process is responsible for performing its own bootstrapping (i.e. allocating/initializing
.data and .bss), after which it should accept messages on the connection and copy data as necessary.
This crate is based on the one in services/test_spawn. The main
difference is that this one has the ability to read, load, and
execute an ELF file through the opcode `LoadElf`.
## API
The following messages are supported:
| Mnemonic | Opcode | Type | Description |
| ---------------- | ------ | ---- | -------------------------------------------------------------------------------------------------------- |
| WriteMemory | 1 | M | Write memory into an area of memory. The `Offset` field is used to determine where the block will start. |
| WriteArgs | 2 | M | Reserved |
| WriteEnvironment | 3 | M | Reserved |
| FinishSetup | 255 | * | Terminate the loop, shutdown the server, and start the program. |
| Mnemonic | Opcode | Type | Description |
|--------------|--------|------|----------------------------------------------------------------------------------------------------------|
| LoadElf | 1 | M | Reads and loads an ELF file sent as a MemoryMessage. `Offset` is used to determine where the file starts |
| PingResponse | 2 | S | Returns the scalar sent except that arg1 += 1 |
## A Note on Building
In case you need to recompile this program for use in `app-loader`,
use the following commands:
```
$ cargo build --package spawn --target riscv32imac-unknown-xous-elf --release
$ cargo run --package tools --bin copy-object target/riscv32imac-unknown-xous-elf/release/spawn
$ cp target/riscv32imac-unknown-xous-elf/release/spawn.bin apps/app-loader/src
```