67cc31a74f
EnterUnwindContext pushes an unwind context (exception handler and/or
finalizer) onto a stack.
LeaveUnwindContext pops the unwind context from that stack.
Upon return to the interpreter loop we check whether the VM has an
exception pending. If no unwind context is available we return from the
loop. If an exception handler is available we clear the VM's exception,
put the exception value into the accumulator register, clear the unwind
context's handler and jump to the handler. If no handler is available
but a finalizer is available we save the exception value + metadata (for
later use by ContinuePendingUnwind), clear the VM's exception, pop the
unwind context and jump to the finalizer.
ContinuePendingUnwind checks whether a saved exception is available. If
no saved exception is available it jumps to the resume label. Otherwise
it stores the exception into the VM.
The Jump after LeaveUnwindContext could be integrated into the
LeaveUnwindContext instruction. I've kept them separate for now to make
the bytecode more readable.
> try { 1; throw "x" } catch (e) { 2 } finally { 3 }; 4
1:
[ 0] EnterScope
[ 10] EnterUnwindContext handler:@4 finalizer:@3
[ 38] EnterScope
[ 48] LoadImmediate 1
[ 60] NewString 1 ("x")
[ 70] Throw
<for non-terminated blocks: insert LeaveUnwindContext + Jump @3 here>
2:
[ 0] LoadImmediate 4
3:
[ 0] EnterScope
[ 10] LoadImmediate 3
[ 28] ContinuePendingUnwind resume:@2
4:
[ 0] SetVariable 0 (e)
[ 10] EnterScope
[ 20] LoadImmediate 2
[ 38] LeaveUnwindContext
[ 3c] Jump @3
String Table:
0: e
1: x
63 lines
1.7 KiB
C++
63 lines
1.7 KiB
C++
/*
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* Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include "Generator.h"
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#include <LibJS/Bytecode/Label.h>
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#include <LibJS/Bytecode/Register.h>
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#include <LibJS/Forward.h>
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#include <LibJS/Heap/Cell.h>
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#include <LibJS/Heap/Handle.h>
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#include <LibJS/Runtime/Exception.h>
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#include <LibJS/Runtime/Value.h>
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namespace JS::Bytecode {
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using RegisterWindow = Vector<Value>;
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class Interpreter {
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public:
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explicit Interpreter(GlobalObject&);
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~Interpreter();
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// FIXME: Remove this thing once we don't need it anymore!
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static Interpreter* current();
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GlobalObject& global_object() { return m_global_object; }
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VM& vm() { return m_vm; }
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Value run(Bytecode::Executable const&);
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ALWAYS_INLINE Value& accumulator() { return reg(Register::accumulator()); }
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Value& reg(Register const& r) { return registers()[r.index()]; }
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void jump(Label const& label)
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{
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m_pending_jump = &label.block();
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}
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void do_return(Value return_value) { m_return_value = return_value; }
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void enter_unwind_context(Optional<Label> handler_target, Optional<Label> finalizer_target);
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void leave_unwind_context();
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void continue_pending_unwind(Label const& resume_label);
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Executable const& current_executable() { return *m_current_executable; }
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private:
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RegisterWindow& registers() { return m_register_windows.last(); }
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VM& m_vm;
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GlobalObject& m_global_object;
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NonnullOwnPtrVector<RegisterWindow> m_register_windows;
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Optional<BasicBlock const*> m_pending_jump;
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Value m_return_value;
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Executable const* m_current_executable { nullptr };
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Vector<UnwindInfo> m_unwind_contexts;
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Handle<Exception> m_saved_exception;
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};
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}
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