Red Bear OS
50 lines
1.3 KiB
Rust
50 lines
1.3 KiB
Rust
use core::mem;
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use syscall::{data::Map, flag::MapFlags, number::SYS_FMAP};
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const STACK_SIZE: usize = 64 * 1024; // 64 KiB
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pub const USERMODE_END: usize = 0x0000_8000_0000_0000;
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pub const STACK_START: usize = USERMODE_END - syscall::KERNEL_METADATA_SIZE - STACK_SIZE;
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static MAP: Map = Map {
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offset: 0,
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size: STACK_SIZE,
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flags: MapFlags::PROT_READ
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.union(MapFlags::PROT_WRITE)
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.union(MapFlags::MAP_PRIVATE)
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.union(MapFlags::MAP_FIXED_NOREPLACE),
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address: STACK_START, // highest possible user address
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};
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core::arch::global_asm!(
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"
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.globl _start
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_start:
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# Setup a stack.
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mov rax, {number}
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mov rdi, {fd}
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mov rsi, offset {map} # pointer to Map struct
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mov rdx, {map_size} # size of Map struct
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syscall
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# Test for success (nonzero value).
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cmp rax, 0
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jg 1f
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# (failure)
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ud2
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1:
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# Subtract 16 since all instructions seem to hate non-canonical RSP values :)
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lea rsp, [rax+{stack_size}-16]
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mov rbp, rsp
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# Stack has the same alignment as `size`.
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call start
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# `start` must never return.
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ud2
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",
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fd = const usize::MAX, // dummy fd indicates anonymous map
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map = sym MAP,
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map_size = const mem::size_of::<Map>(),
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number = const SYS_FMAP,
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stack_size = const STACK_SIZE,
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);
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