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by hayley-patton
978 days ago
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gencgc uses software protection on some but not all architectures -- I recall x86-64 and MIPS but not ARM though. On x86-64 with SBCL 2.3.8 for example: * (disassemble #'(setf svref))
; disassembly for (SETF SVREF)
; Size: 39 bytes. Origin: #x5349B00D ; (SETF SVREF)
; 0D: 483B77F9 CMP RSI, [RDI-7]
; 11: 731D JAE L0
; 13: 488D44B701 LEA RAX, [RDI+RSI*4+1]
↓ card marking here
; 18: 48C1E80A SHR RAX, 10
; 1C: 25FFFF0F00 AND EAX, 1048575
; 21: 41C6040400 MOV BYTE PTR [R12+RAX], 0
↓ pointer store here
; 26: 488954B701 MOV [RDI+RSI*4+1], RDX
; 2B: C9 LEAVE
; 2C: F8 CLC
; 2D: C3 RET
; 2E: CC10 INT3 16 ; Invalid argument count trap
; 30: L0: CC24 INT3 36 ; INVALID-VECTOR-INDEX-ERROR
; 32: 1C BYTE #X1C ; RDI(d)
; 33: 19 BYTE #X19 ; RSI(a)
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