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61 lines
2.8 KiB
61 lines
2.8 KiB
4 months ago
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Extending the disassembler
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==========================
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The output of the disassembler can be extended and customized. This may be
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useful for example to add comments and annotations to the disassembly, print
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aliases for register names, or add an offset to disassembled addresses.
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The general procedure to achieve this is to create a sub-class of
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`Disassembler` and override the appropriate virtual functions.
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The `Disassembler` class provides virtual methods that implement how specific
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disassembly elements are printed. See
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[src/aarch64/disasm-aarch64.h](/src/aarch64/disasm-aarch64.h) for details.
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These include functions like:
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virtual void AppendRegisterNameToOutput(const Instruction* instr,
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const CPURegister& reg);
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virtual void AppendPCRelativeOffsetToOutput(const Instruction* instr,
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int64_t offset);
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virtual void AppendCodeRelativeAddressToOutput(const Instruction* instr,
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const void* addr);
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virtual void AppendCodeRelativeCodeAddressToOutput(const Instruction* instr,
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const void* addr);
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They can be overridden for example to use different register names and annotate
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code addresses.
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More complex modifications can be performed by overriding the visitor functions
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of the disassembler. The VIXL `Decoder` uses a visitor pattern implementation,
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so the `Disassembler` (as a sub-class of `DecoderVisitor`) must provide a
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visitor function for each sub-type of instructions. The complete list of
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visitors is defined by the macro `VISITOR_LIST` in
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[src/aarch64/decoder-aarch64.h](/src/aarch64/decoder-aarch64.h).
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The [/examples/custom-disassembler.h](/examples/custom-disassembler.h) and
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[/examples/custom-disassembler.cc](/examples/custom-disassembler.cc) example
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files show how the methods can be overridden to use different register names,
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map code addresses, annotate code addresses, and add comments:
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VIXL disasm 0x7fff04cb05e0: add x10, x16, x17
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custom disasm -0x8: add x10, ip0, ip1 // add/sub to x10
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VIXL disasm 0x7fff04cb05e4: cbz x10, #+0x28 (addr 0x7fff04cb060c)
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custom disasm -0x4: cbz x10, #+0x28 (addr 0x24 ; label: somewhere)
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VIXL disasm 0x7fff04cb05e8: add x11, x16, x17
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custom disasm 0x0: add x11, ip0, ip1
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VIXL disasm 0x7fff04cb05ec: add w5, w6, w30
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custom disasm 0x4: add w5, w6, w30
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VIXL disasm 0x7fff04cb05f0: tbz w10, #2, #-0x10 (addr 0x7fff04cb05e0)
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custom disasm 0x8: tbz w10, #2, #-0x10 (addr -0x8)
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One can refer to the implementation of visitor functions for the `Disassembler`
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(in [src/aarch64/disasm-aarch64.cc](/src/aarch64/disasm-aarch64.cc)) or even
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for the `Simulator`
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(in [src/aarch64/simulator-aarch64.cc](/src/aarch64/simulator-aarch64.cc))
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to see how to extract information from instructions.
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