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riscv-rt: validate hard ID earlier and allow abort to be located anywhere #308

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Merged
romancardenas merged 1 commit into from
Jun 25, 2025
Merged

riscv-rt: validate hard ID earlier and allow abort to be located anywhere #308

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6 changes: 4 additions & 2 deletions riscv-rt/CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -9,11 +9,13 @@ and this project adheres to [Semantic Versioning](http://semver.org/).

### Changed

- Main function no longer needs to be close to _start. A linker script may copy
all code to RAM and keep .init in flash/ROM.
- `main` function no longer needs to be close to `_start`. A linker script may copy
all code to RAM and keep `.init` in flash/ROM.
- By default, the stack is now split into equal parts based on the number of
harts.
- In M-mode, the hart ID is moved to `a0` at the beginning of the runtime.
- `abort` function no longer needs to be close to `_start`.
- In multi-hart targets, the hart ID is now validated earlier in the boot process.

### Fixed

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11 changes: 8 additions & 3 deletions riscv-rt/src/asm.rs
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Expand Up @@ -72,6 +72,14 @@ _abs_start:
"csrw stvec, t0",
#[cfg(not(feature = "s-mode"))]
"csrw mtvec, t0",
// If multi-hart, assert that hart ID is valid
#[cfg(not(feature = "single-hart"))]
"lui t0, %hi(_max_hart_id)
add t0, t0, %lo(_max_hart_id)
bgeu t0, a0, 1f
la t0, abort // If hart_id > _max_hart_id, jump to abort
jr t0
1:", // only valid harts reach this point
);

// ZERO OUT GENERAL-PURPOSE REGISTERS
Expand All @@ -91,9 +99,6 @@ cfg_global_asm!(
#[cfg(not(feature = "single-hart"))]
cfg_global_asm!(
"mv t2, a0
lui t0, %hi(_max_hart_id)
add t0, t0, %lo(_max_hart_id)
bgtu t2, t0, abort
lui t0, %hi(_hart_stack_size)
add t0, t0, %lo(_hart_stack_size)",
#[cfg(riscvm)]
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