e6d43a23ac
Bundles state that lives OUTSIDE the xenia-rs repo so a fresh clone on
another machine can be brought up to identical configuration via
migration/setup.sh:
- claude-memory/ ~/.claude/projects/-home-fabi-RE-Project-Sylpheed/memory/
(103 files, 1.1 MB - MEMORY.md + every
project_xenia_rs_*.md from audits
addis_signext through audit-058)
- project-root/dot-claude/ <project-root>/.claude/settings.json
(Stop hook + permissions)
- project-root/ppc-manual/ <project-root>/ppc-manual/
(PowerPC reference docs, 397 files, 3.7 MB)
- project-root/run-canary.sh <project-root>/run-canary.sh
- README.md Human-readable setup checklist
- setup.sh Idempotent installer (also reclones
xenia-canary at pinned HEAD 6de80dffe)
- MANIFEST.md Per-file mapping + per-file-not-bundled
restoration recipe
Excluded from bundle (not shippable via git):
- Sylpheed ISO (7.8 GB; copyright; manual copy required)
- sylpheed.db (395 MB; regenerable from XEX via analysis tooling)
- target/ build artifacts (rebuild on target)
- audit-runs probe firehoses (.log/.stdout/.stderr ~11 GB; rerun if needed)
- audit-runs memory dumps (.bin ~4.5 GB; rerun audit-026/027/029 if needed)
- xenia-canary checkout (setup.sh reclones from
git.mc02.dev/fabi/Xenia-Canary.git at HEAD 6de80dffe)
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
122 lines
4.8 KiB
Markdown
122 lines
4.8 KiB
Markdown
# `extsbx` — Extend Sign Byte
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> **Category:** [Integer ALU](../categories/alu.md) · **Form:** [X](../forms/X.md) · **Opcode:** `0x7c000774`
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<!-- GENERATED: BEGIN -->
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## Assembler Mnemonics
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| Mnemonic | XML entry | Flags | Description |
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| --- | --- | --- | --- |
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| `extsb` | `extsbx` | — | Extend Sign Byte |
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| `extsb.` | `extsbx` | Rc=1 | Extend Sign Byte |
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## Syntax
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```asm
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extsb[Rc] [RA], [RS]
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```
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## Encoding
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### `extsbx` — form `X`
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- **Opcode word:** `0x7c000774`
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- **Primary opcode (bits 0–5):** `31`
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- **Extended opcode:** `954`
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- **Synchronising:** no
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| Bits | Field | Meaning |
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| --- | --- | --- |
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| 0–5 | `OPCD` | primary opcode |
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| 6–10 | `RT/FRT/VRT` | destination |
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| 11–15 | `RA/FRA/VRA` | source A |
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| 16–20 | `RB/FRB/VRB` | source B |
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| 21–30 | `XO` | extended opcode (10 bits) |
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| 31 | `Rc` | record-form flag |
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## Operands
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| Field | Role | Description |
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| --- | --- | --- |
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| `RS` | extsbx: read | Source GPR (alias for RD in some stores). |
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| `RA` | extsbx: write | Source GPR (`r0`–`r31`). |
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| `CR` | extsbx: write (conditional) | Condition-register update. When `Rc=1`, CR field 0 (or CR6 for vector compares, CR1 for FPU) is updated from the result. |
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## Register Effects
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### `extsbx`
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- **Reads (always):** `RS`
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- **Reads (conditional):** _none_
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- **Writes (always):** `RA`
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- **Writes (conditional):** `CR`
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## Status-Register Effects
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- `extsbx`: **CR0** ← signed-compare(result, 0) with `SO ← XER[SO]`, when `Rc=1`.
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## Operation (pseudocode)
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```
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RA <- EXTS_8_to_64((RS)[56:63])
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```
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## C Translation Example
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```c
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/* C translation: the xenia-rs interpreter arm below in */
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/* Implementation References is the authoritative semantic */
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/* snapshot. Translate it line-by-line: */
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/* - ctx.gpr[N] -> r[N] (or f[]/v[] for FPRs/VRs) */
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/* - mem.read_u*/write_u* -> mem_read_u*_be / mem_write_u*_be */
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/* - ctx.update_cr_signed(fld, v) -> update_cr_signed(fld, v) */
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/* - ctx.xer_ca / xer_ov / xer_so -> xer.CA / xer.OV / xer.SO */
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/* The Register Effects and Status-Register Effects tables above */
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/* enumerate every side effect a faithful translation must emit. */
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```
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## Implementation References
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**`extsbx`**
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- xenia-canary XML: [`tools/ppc-instructions.xml` — search for `mnem="extsbx"`](../../xenia-canary/tools/ppc-instructions.xml)
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- xenia-canary emit: [`src/xenia/cpu/ppc/ppc_emit_alu.cc:714`](../../xenia-canary/src/xenia/cpu/ppc/ppc_emit_alu.cc#L714)
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- xenia-rs opcode: [`crates/xenia-cpu/src/opcode.rs:25`](../../xenia-rs/crates/xenia-cpu/src/opcode.rs#L25)
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- xenia-rs decoder: [`crates/xenia-cpu/src/decoder.rs:849`](../../xenia-rs/crates/xenia-cpu/src/decoder.rs#L849)
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- xenia-rs interpreter: [`crates/xenia-cpu/src/interpreter.rs:589-595`](../../xenia-rs/crates/xenia-cpu/src/interpreter.rs#L589-L595)
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<details><summary>xenia-rs interpreter body (frozen snapshot)</summary>
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```rust
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PpcOpcode::extsbx => {
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// PPCBUG-034: 32-bit ABI — sign-extend byte to i32, write zero-extended.
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// PPCBUG-036 (coupled): CR0 must view result as i32, not i64.
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ctx.gpr[instr.ra()] = ctx.gpr[instr.rs()] as i8 as i32 as u32 as u64;
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if instr.rc_bit() { ctx.update_cr_signed(0, ctx.gpr[instr.ra()] as u32 as i32 as i64); }
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ctx.pc += 4;
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}
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```
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</details>
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<!-- GENERATED: END -->
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## Special Cases & Edge Conditions
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- **Sign-extends the low 8 bits of `RS` to 64 bits.** Bit 56 of `RS` (the sign bit of the byte) becomes bits 0–55 of `RA`; bits 56–63 are copied verbatim.
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- **Common after a byte load.** `lbz` zero-extends from memory; `extsb` converts the result to a signed-byte view. Many compilers emit this pair; the recent ISA `lba`/`lbau` family is *not* available on the Xenon, so this two-instruction sequence is the canonical pattern.
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- **`Rc=1` updates CR0 from the full 64-bit signed value** — but xenia-rs truncates to 32 bits in [`interpreter.rs:384`](../../xenia-rs/crates/xenia-cpu/src/interpreter.rs#L384). For `extsb.` this is harmless because the result fits in 8 bits sign-extended; the low 32 bits already encode the sign correctly.
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- **Operand convention** is the X-form one (`RA` destination, `RS` source). Same as the rest of the logical family.
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- **No `XER` side effects.**
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- **`RB` field unused.** Set to 0 by assemblers; ignored on decode.
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- **Aliasing is fine.** `extsb r3, r3` rewrites `r3` in place.
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## Related Instructions
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- [`extshx`](extshx.md) — sign-extend half-word (16 bits).
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- [`extswx`](extswx.md) — sign-extend word (32 bits).
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- [`rlwinmx`](rlwinmx.md), [`rldiclx`](rldiclx.md) — for *zero*-extending or extracting non-byte-aligned fields.
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- `lbz`, `lha` (memory ops, outside this page set) — pair with this for signed byte loads.
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## IBM Reference
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- [AIX 7.3 — `extsb` (Extend Sign Byte)](https://www.ibm.com/docs/en/aix/7.3.0?topic=set-extsb-extend-sign-byte-instruction)
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