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51 lines
1.3 KiB
Nim
51 lines
1.3 KiB
Nim
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# Sourced from https://forum.nim-lang.org/t/9255#60617
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import posix
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type
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Instr {.union.} = object
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bytes: array[8, byte]
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value: uint64
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proc mockImpl(target, replacement: pointer) =
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# YOLO who needs alignment
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#doAssert (cast[ByteAddress](target) and ByteAddress(0x07)) == 0
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var page = cast[pointer](cast[ByteAddress](target) and (not 0xfff))
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doAssert mprotect(page, 4096, PROT_WRITE or PROT_EXEC) == 0
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let rel = cast[ByteAddress](replacement) - cast[ByteAddress](target) - 5
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var
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instr =
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Instr(
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bytes: [
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0xe9.byte,
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(rel shr 0).byte,
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(rel shr 8).byte,
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(rel shr 16).byte,
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(rel shr 24).byte,
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0,
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0,
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0
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]
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)
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cast[ptr uint64](target)[] = instr.value
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doAssert mprotect(page, 4096, PROT_EXEC) == 0
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# Note: Requires manual cleanup
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# Usage Example:
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# proc helloWorld(): string =
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# "Hello, World!"
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#
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# echo helloWorld() # "Hello, World!"
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#
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# let backup = helloWorld
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# mock(helloWorld):
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# proc mockedHellWorld(): string =
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# "Mocked Hello, World!"
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# mockedMigrate
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#
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# echo helloWorld() # "Mocked Hello, World!"
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#
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# helloWorld = backup # Restore the original function
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template mock*(target, replacement: untyped): untyped =
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mockImpl(cast[pointer](target), cast[pointer](replacement))
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