Rosetta runs AVX2, FMA, BMI1/2, F16C and MOVBE, but, unlike an Intel
host, it has neither RDSEED, CLWB nor RDPID. --to-rosetta converts
everything --to-intel does and lowers these three as well:
- RDSEED becomes RDRAND (the /6 form of the same opcode), which also
returns a random value and sets CF.
- CLWB only writes a cache line back, so it becomes a NOP of the same
length.
- RDPID becomes a load of 0 through an optional stub: Rosetta's TSC_AUX
is a constant, not a processor index, so every thread reports
processor 0. A site with no movable instruction after it for the jump
is kept.
The flag implies --to-intel and conflicts with --windows. It is
independent of --macos: it only changes what the conversion produces, so
--macos alone leaves these instructions as they are, as on an Intel Mac,
and a title for Rosetta is relinked with --macos --to-rosetta. Intel
output is unchanged: the target is a parameter of the converter, Intel by
default.
SHA-1 and SHA-256 instructions with a [rip+disp32] operand, and
instructions with one that a short site absorbs, now move into the
stub. The stub records each displacement as a relocation relative to
the site, and the Linux, guest and Windows placements resolve it once
the stub address is known. Indirect branches through [rip+disp32]
still fail the relink.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Each in-place substitution went through X64InstructionRewriter::Rewrite,
which copies the whole code segment and decodes every instruction in it
to adjust references. The converter only accepts equal-length
replacements, so the adjustment is always zero and the copy and scan are
wasted: conversion time grew by one segment scan per substitution. Copy
the replacement bytes into the segment instead.
RSQRTPS and RCPPS are approximations whose low bits differ between Intel
and AMD. Intel returns 0x3F7FF000 for 1/sqrt(1.0), and two Newton-Raphson
steps on it settle on 0.99999994 instead of 1.0. PPSA21564 renormalises
its spring quaternions that way: an identity quaternion keeps w at
0.99999994 with a zero axis, its axis-angle conversion then normalises the
zero axis into NaNs, and the NaN bone poses reach keyframed physics bodies.
A NaN body later moves to an invalid broadphase cell and the game crashes
a few seconds into its hub level.
--to-intel now replaces the VEX.128 register forms with an out-of-line stub
that computes 1/sqrt(x) with SQRTPS and DIVPS (1/x with DIVPS), keeping
the upper half of the destination cleared and the scratch register intact.
A site with no room for the jump, including one followed by a branch
target or a RIP-relative instruction, keeps the native instruction and is
reported as kept instead of failing the relink.
In 64-bit mode a REX prefix only takes effect when it immediately
precedes the opcode; a REX followed by a legacy prefix or another REX is
ignored. The instruction decoder, the rewriter's reference classifier,
DecodedInstruction and the SSE4a, SHA-256 and CLZERO operand decoders
read legacy prefixes and then at most one REX. `48 F3 0F 2B 00`
(MOVNTSS) was therefore scanned as `[48 F3][0F 2B 00]` and kept, and
`48 67 0F 01 FC` lost its address-size prefix.
All of them now accept REX bytes among the prefixes and keep only one
that directly precedes the opcode. The converter's guard against
prefix-only fragments is removed, since the decoder no longer produces
them, and the TechnicalDebt entry describing the split is dropped.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Lower CLZERO out of line instead of failing the relink: the 64-byte line
containing rAX (EAX with 67h) is cleared with four MOVNTDQ stores of
zero, the same non-temporal, weakly ordered store. The line address is
masked in xmm0 so RFLAGS stays untouched; xmm0 and rcx are spilled below
the red zone. Short sites share stubs through MatchSequence. CLZERO with
LOCK, an FS/GS override, a 66/F2/F3 prefix or longer than 15 bytes fails
the relink.
The decoder splits a REX followed by another prefix into a separate
instruction, which would hide a prefix that changes what CLZERO or the
next instruction does. The converter now fails the relink when such a
prefix-only fragment directly precedes an AMD-only instruction or would
be moved into a stub as a trailing instruction.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
EXTRQ, INSERTQ, MOVNTSS and MOVNTSD are rewritten at relink time: same-length in-place forms
where they exist, otherwise a jmp rel32 into an appended executable section holding a
scratch-free SSE body and a jump back, so no code shifts and no RIP-relative or jump-table
operand needs adjusting. Decoder fixes for POPCNT and 0F BB (BTC), codegen and elfpatcher
tests, README and technical-debt notes. The runtime illegal-instruction trap stays as a
fallback.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0177gthrWEBBfBu5xJDXgBfo
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