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Jump-and-link instruction #630

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Merged
Dentosal merged 6 commits into from
Jul 28, 2025
Merged

Jump-and-link instruction #630

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3e8c8af
Add JAL instruction
Dentosal Mar 14, 2025
023cd4b
Merge branch 'master' into dento/jal-instruction
Dentosal Mar 24, 2025
8d726c8
Correctly use imm * 4 in all fields
Dentosal Mar 27, 2025
b33db4c
Merge branch 'master' into dento/jal-instruction
Dentosal Apr 14, 2025
17eb8f3
Merge branch 'master' into dento/jal-instruction
Dentosal May 13, 2025
5682a25
Merge branch 'master' into dento/jal-instruction
Dentosal Jun 26, 2025
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16 changes: 16 additions & 0 deletions src/fuel-vm/instruction-set.md
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Original file line number Diff line number Diff line change
Expand Up @@ -61,6 +61,7 @@
- [`JNZF`: Jump if not zero relative forwards](#jnzf-jump-if-not-zero-relative-forwards)
- [`JNEB`: Jump if not equal relative backwards](#jneb-jump-if-not-equal-relative-backwards)
- [`JNEF`: Jump if not equal relative forwards](#jnef-jump-if-not-equal-relative-forwards)
- [`JAL`: Jump and link](#jal-jump-and-link)
- [`RET`: Return from context](#ret-return-from-context)
- [Memory Instructions](#memory-instructions)
- [`ALOC`: Allocate memory](#aloc-allocate-memory)
Expand Down Expand Up @@ -1299,6 +1300,21 @@ Panic if:

- `$pc + ($rC + imm + 1) * 4 > VM_MAX_RAM - 1`

### `JAL`: Jump and link

| | |
|-------------|-----------------------------------------------------------------------------------------------|
| Description | Set `$rA` to address of the next instruction. Jump to instruction at address `$rB + imm * 4`. |
| Operation | `if $rA is not $zero { $rA = $pc + 4 }` <br> `$pc = $rB + imm * 4` |
| Syntax | `jal $rA $rB imm` |
| Encoding | `0x00 rA rB i i` |
| Notes | If `$rA` is `$zero`, the return address discarded. |

Panic if:

- `$rA` is a reserved register other than `$zero`
- `$rB + imm * 4 >= VM_MAX_RAM`

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@Voxelot Voxelot May 12, 2025

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Should we panic if $rB == $pc && imm == 0 to avoid jumping into the exact same spot?

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@Dentosal Dentosal May 13, 2025

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Likely not. It's not like you couldn't otherwise make an infinite loop if you want, and then you'll just run out of gas anyway.

### `RET`: Return from context

| | |
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