52 lines
1.9 KiB
C++
52 lines
1.9 KiB
C++
//---
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// fxos.disasm-passes.cfg: Control Flow Graph construction
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//
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// This pass explores functions and computes the [jmptarget] field of concrete
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// instructions as it goes. This is required for other passes that work by
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// traversing the CFG, such as the abstract interpretor.
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//
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// This is the main exploration pass. Other passes do not typically load new
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// instructions from the underlying disassembly. Straightforward passes such as
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// [print] iterate on instructions loaded by this pass.
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//
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// The main gimmick of this pass is to "resolve delay slots" by forcing down
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// the properties of delayed instructions into their respective delay slots.
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// For instance, in
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// jmp @r0
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// mov #1, r4
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// the jump is delayed until after the move. To handle this, fxos makes the jmp
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// a no-op and applies dual move-jump semantics to the mov below it.
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//
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// This could be tricky for the abstract interpreter because the jump target
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// has to be computed with the environment before the jmp, which is not
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// available when considering the mov. Luckily all delayed jumps are state
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// no-ops so the state before the mov can be used instead.
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//
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// Note that jumping into a delay slot will activate the jump in fxos, which is
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// not the actual behavior of the processor. fxos usually complains about the
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// crazy compiler when this occurs. Note that if it happens but we don't know
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// that it's a delay slot (ie. the instruction from above is never executed in
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// the current function), then everything's fine.
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//
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// Take-home message: delay slots are a pain to analyze, so we get rid of them
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// as soon as possible and proceed with normal semantics.
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//---
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#ifndef LIBFXOS_DISASM_PASSES_CFG_H
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#define LIBFXOS_DISASM_PASSES_CFG_H
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#include <fxos/disassembly.h>
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namespace FxOS {
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class CfgPass: public DisassemblyPass
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{
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public:
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CfgPass(Disassembly &disasm);
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void analyze(uint32_t pc, ConcreteInstruction &inst) override;
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};
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} /* namespace FxOS */
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#endif /* LIBFXOS_DISASM_PASSES_CFG_H */
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