Skip to content

fix(#378): fail honestly on out-of-layout local — never guess a frame offset #379

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
avrabe merged 1 commit into from
Jun 19, 2026
Merged

fix(#378): fail honestly on out-of-layout local — never guess a frame offset #379

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
65 changes: 29 additions & 36 deletions crates/synth-synthesis/src/instruction_selector.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -5579,24 +5579,19 @@ impl InstructionSelector {
});
(dst, false)
} else {
// Local not in layout (shouldn't happen for valid wasm,
// but fall back to legacy behaviour for compatibility).
let dst = alloc_temp_or_spill(
&mut next_temp,
&mut stack,
&mut instructions,
&mut spill,
&live_params,
idx,
)?;
instructions.push(ArmInstruction {
op: ArmOp::Ldr {
rd: dst,
addr: MemAddr::imm(Reg::SP, (*local_idx as i32 - 4) * 4),
},
source_line: Some(idx),
});
(dst, false)
// #378 honesty: a local absent from the computed frame
// layout is either malformed wasm (out-of-range index,
// which validation should have rejected) or a
// layout-computation bug. Either way, FAIL HONESTLY —
// a loud `Err` loud-skips the function — rather than
// GUESS a frame offset `(local_idx-4)*4` and silently
// miscompile. Same never-guess contract as GI-FPU-001
// (decoder) and #180/#185 (encoder Ok-or-Err).
return Err(synth_core::Error::synthesis(format!(
"local.get {local_idx} (op {idx}) is absent from the \
computed frame layout — refusing to guess a stack \
offset (would silently miscompile)"
)));
};
stack.push(StackVal::Reg {
reg,
Expand Down Expand Up @@ -8072,15 +8067,14 @@ impl InstructionSelector {
});
cf.add_instruction();
} else {
// Fall-through for compatibility (shouldn't happen).
instructions.push(ArmInstruction {
op: ArmOp::Str {
rd: val,
addr: MemAddr::imm(Reg::SP, (*local_idx as i32 - 4) * 4),
},
source_line: Some(idx),
});
cf.add_instruction();
// #378 honesty: refuse to guess a frame offset for a local
// absent from the layout — fail loud (loud-skip) rather than
// silently store to a guessed address. See LocalGet above.
return Err(synth_core::Error::synthesis(format!(
"local.set {local_idx} (op {idx}) is absent from the \
computed frame layout — refusing to guess a stack \
offset (would silently miscompile)"
)));
}
}

Expand Down Expand Up @@ -8162,15 +8156,14 @@ impl InstructionSelector {
});
cf.add_instruction();
} else {
// Fall-through for compatibility.
instructions.push(ArmInstruction {
op: ArmOp::Str {
rd: val,
addr: MemAddr::imm(Reg::SP, (*local_idx as i32 - 4) * 4),
},
source_line: Some(idx),
});
cf.add_instruction();
// #378 honesty: refuse to guess a frame offset for a local
// absent from the layout — fail loud (loud-skip) rather than
// silently store to a guessed address. See LocalGet above.
return Err(synth_core::Error::synthesis(format!(
"local.tee {local_idx} (op {idx}) is absent from the \
computed frame layout — refusing to guess a stack \
offset (would silently miscompile)"
)));
}
}

Expand Down
Loading