CHARLES UNIVERSITY IN PRAGUE

http://d3s.mff.cuni.cz/~jezek

faculty of mathematics and physics

Principles of Computers17th Lecture

Pavel Ježek, Ph.D.pavel.jezek@d3s.mff.cuni.cz

Selected Faults/Traps/Exceptions of x86 ISA

CPU Exception Interrupt vector(all push IP of faulting instruction)

Invalid opcode 6

Divide by zero (DIV0) 0

Alignment check 17 ($11)

General Protection Fault 13 ($0D)

Page Fault 14 ($0E)

kernel initcall Exec(‘shell.exe’) load shell.exe call shell.exe entrypoint ... repeat ... until key <> ENTER call Exec(‘P.EXE’) load P.EXE load & relocate EXE image ... ... ... ... call P.EXE entrypoint ... ... main program of P.EXE ...

kernel initcall Exec(‘shell.exe’) load shell.exe call shell.exe entrypoint ... repeat ... until key <> ENTER call Exec(‘P.EXE’) load P.EXE load & relocate EXE image load & relocate DLL images (A.DLL, B.DLL) ... ... call A.DLL entrypoint call B.DLL entrypoint call P.EXE entrypoint ... ... main program of P.EXE ...

Dependency Walker (depends.exe)

Process Explorerwww.sysinternals.com

Really Dynamic DLL Loading Example

...

kerneldata

IVTproc table...

page tbl kernel code

kernel codestackstack

guard pagefreefreefreefreefreefreefree

... free

... free

... free9 free8 A data7 A data6 A data5 A code4 A code3 A code2 A code1 A codePT ...

→ call procedure at address 4000 (= in page 3 for 1kB pages)

Non-presentKernel/SupervisorUser Read/OnlyUser Read/Write

→ read variable at address 8200 (= in page 8 for 1kB pages)

A’s entrypoint

...

kerneldata

IVTproc table...

page tbl kernel code

kernel codestackstack

guard pagefreefreefreefreefreefreefree

... free

... free

... free9 free8 A data (guard)7 A data (guard)6 A data (guard)5 A code (guard)4 A code (guard)3 A code (guard)2 A code (guard)1 A codePT ...

Non-presentKernel/SupervisorUser Read/OnlyUser Read/Write

A’s entrypoint

...

kerneldata

IVTproc table...

page tbl kernel code

kernel codestackstack

guard pagefreefreefreefreefreefreefree

... free

... free

... free9 free8 A data (guard)7 A data (guard)6 A data (guard)5 A code (guard)4 A code (guard)3 A code (guard)2 A code (guard)1 A codePT ...

Non-presentKernel/SupervisorUser Read/OnlyUser Read/Write

A’s entrypoint

→ call procedure at address 4000 (= in page 3 for 1kB pages)

page fault

...

kerneldata

IVTproc table...

page tbl kernel code

kernel codestackstack

guard pagefreefreefreefreefreefreefree

... free

... free

... free9 free8 A data (guard)7 A data (guard)6 A data (guard)5 A code (guard)4 A code (guard)3 A code2 A code (guard)1 A codePT ...

Non-presentKernel/SupervisorUser Read/OnlyUser Read/Write

A’s entrypoint

→ call procedure at address 4000 (= in page 3 for 1kB pages)

...

kerneldata

IVTproc table...

page tbl kernel code

kernel codestackstack

guard pagefreefreefreefreefreefreefree

... free

... free

... free9 free8 A data (guard)7 A data (guard)6 A data (guard)5 A code (guard)4 A code (guard)3 A code2 A code (guard)1 A codePT ...

Non-presentKernel/SupervisorUser Read/OnlyUser Read/Write

A’s entrypoint

→ call procedure at address 4000 (= in page 3 for 1kB pages)

→ read variable at address 8200 (= in page 8 for 1kB pages)

page fault

...

kerneldata

IVTproc table...

page tbl kernel code

kernel codestackstack

guard pagefreefreefreefreefreefreefree

... free

... free

... free9 free8 A data7 A data (guard)6 A data (guard)5 A code (guard)4 A code (guard)3 A code2 A code (guard)1 A codePT ...

Non-presentKernel/SupervisorUser Read/OnlyUser Read/Write

A’s entrypoint

→ call procedure at address 4000 (= in page 3 for 1kB pages)

→ read variable at address 8200 (= in page 8 for 1kB pages)

page fault

kernel initcall Exec(‘shell.exe’) load shell.exe call shell.exe entrypoint ... repeat ... until key <> ENTER call Exec(‘P.EXE’) load P.EXE load & relocate EXE image load & relocate DLL images (A.DLL, B.DLL) ... ... call A.DLL entrypoint call B.DLL entrypoint call P.EXE entrypoint ... ... main program of P.EXE ...

kernel initcall Exec(‘shell.exe’) load shell.exe call shell.exe entrypoint ... repeat ... until key <> ENTER call Exec(‘P.EXE’) load P.EXE load & relocate EXE image load & relocate DLL images (A.DLL, B.DLL) ... ... call A.DLL entrypoint call B.DLL entrypoint call P.EXE entrypoint ... ... call Exit clean up (release resources) ... ... ... (never here = rest of P.EXE main program) ... ... ret goto

kernel initcall Exec(‘shell.exe’) load shell.exe call shell.exe entrypoint ... repeat ... until key <> ENTER call Exec(‘P.EXE’) load P.EXE load & relocate EXE image load & relocate DLL images (A.DLL, B.DLL) ... ... call A.DLL entrypoint call B.DLL entrypoint call P.EXE entrypoint ... ... call Exit clean up (release resources) ... ret ... should not get here ... ... ret goto

...

...shell’s entrypoint

argumentsreturn address

shell → kernelInit Exec syscall

argumentsreturn address

Exec → shellP.EXE’s entrypoint

argumentsreturn address

P main → ExecExit syscallarguments

SP →return address

Exit → P main........................

IP

kernel initcall Exec(‘shell.exe’) load shell.exe call shell.exe entrypoint ... repeat ... until key <> ENTER call Exec(‘P.EXE’) load P.EXE load & relocate EXE image load & relocate DLL images (A.DLL, B.DLL) ... ... call A.DLL entrypoint call B.DLL entrypoint call P.EXE entrypoint ... ... call Exit clean up (release resources) ... ret ... P.EXE’s main program continues ... ... ret goto

...

...shell’s entrypoint

argumentsreturn address

shell → kernelInit Exec syscall

argumentsreturn address

Exec → shellP.EXE’s entrypoint

argumentsreturn address

P main → Exec

SP →Exit syscallarguments

return addressExit → P main

...

...

...

...

...

...

...

...

IP

kernel initcall Exec(‘shell.exe’) load shell.exe call shell.exe entrypoint ... repeat ... until key <> ENTER call Exec(‘P.EXE’) load P.EXE load & relocate EXE image load & relocate DLL images ... ... call A.DLL entrypoint call B.DLL entrypoint call P.EXE entrypoint ... ... call Exit clean up (release resources) SP := SP + sizeof(Exit stack frame) ret ... (never here = rest of P.EXE main program) ... ... ret goto

...

...shell’s entrypoint

argumentsreturn address

shell → kernelInit Exec syscall

argumentsreturn address

Exec → shellP.EXE’s entrypoint

argumentsreturn address

P main → ExecExit syscallarguments

SP →return address

Exit → P main........................

IP

kernel initcall Exec(‘shell.exe’) load shell.exe call shell.exe entrypoint ... repeat ... until key <> ENTER call Exec(‘P.EXE’) load P.EXE load & relocate EXE image load & relocate DLL images ... ... call A.DLL entrypoint call B.DLL entrypoint call P.EXE entrypoint ... ... call Exit clean up (release resources) SP := SP + sizeof(Exit stack frame) ret ... (never here = rest of P.EXE main program) ... ... ret goto

...

...shell’s entrypoint

argumentsreturn address

shell → kernelInit Exec syscall

argumentsreturn address

Exec → shellP.EXE’s entrypoint

arguments

SP →return address

P main → ExecExit syscallarguments

return addressExit → P main

...

...

...

...

...

...

...

...

IP

kernel initcall Exec(‘shell.exe’) load shell.exe call shell.exe entrypoint ... repeat ... until key <> ENTER call Exec(‘P.EXE’) load P.EXE load & relocate EXE image load & relocate DLL images ... ... call A.DLL entrypoint call B.DLL entrypoint call P.EXE entrypoint ... ... call Exit clean up (release resources) SP := SP + sizeof(Exit stack frame) ret ... (never here = rest of P.EXE main program) ... ... ret goto

...

...shell’s entrypoint

argumentsreturn address

shell → kernelInit Exec syscall

argumentsreturn address

Exec → shell

SP →P.EXE’s entrypoint

argumentsreturn address

P main → ExecExit syscallarguments

return addressExit → P main

...

...

...

...

...

...

...

...

IP

kernel initcall Exec(‘shell.exe’) load shell.exe call shell.exe entrypoint ... repeat ... until key <> ENTER call Exec(‘P.EXE’) load P.EXE load & relocate EXE image load & relocate DLL images push currentPID currentPID := AllocateNewPID; call A.DLL entrypoint call B.DLL entrypoint call P.EXE entrypoint ... ... call Exit clean up (release resources) SP := SP + sizeof(Exit stack frame) ret ... (never here = rest of P.EXE main program) ... pop currentPID ret goto

context switch

context switch

kernel initcall Exec(‘shell.exe’) load shell.exe call shell.exe entrypoint ... AllocMem → for currentPID = 1 repeat ... until key <> ENTER call Exec(‘P.EXE’) load P.EXE load & relocate EXE image load & relocate DLL images push currentPID (1) currentPID := AllocateNewPID; (2) call A.DLL entrypoint call B.DLL entrypoint call P.EXE entrypoint ... ... AllocMem → for currentPID = 2 call Exit clean up (release resources) SP := SP + sizeof(Exit stack frame) ret ... (never here = rest of P.EXE main program) ... pop currentPID (1) ret goto

context switch to PID 2

context switch back to PID 1

1) Allocated memory (pages)

kernel initcall Exec(‘shell.exe’) load shell.exe call shell.exe entrypoint ... AllocMem → for currentPID = 1 repeat ... until key <> ENTER call Exec(‘P.EXE’) load P.EXE load & relocate EXE image load & relocate DLL images push currentPID (1) currentPID := AllocateNewPID; (2) call A.DLL entrypoint call B.DLL entrypoint call P.EXE entrypoint ... ... AllocMem → for currentPID = 2 call Exit clean up (release resources) SP := SP + sizeof(Exit stack frame) ret ... (never here = rest of P.EXE main program) ... pop currentPID (1) ret goto

context switch to PID 2

context switch back to PID 1

1) Allocated memory (pages)2) CPU fault → kernel interrupt handler →

call procTable[currentPID].faultHandlers[faultID]

kernel initcall Exec(‘shell.exe’) load shell.exe call shell.exe entrypoint ... AllocMem → for currentPID = 1 repeat ... until key <> ENTER call Exec(‘P.EXE’) load P.EXE load & relocate EXE image load & relocate DLL images push currentPID (1) currentPID := AllocateNewPID; (2) call A.DLL entrypoint call B.DLL entrypoint call P.EXE entrypoint ... ... AllocMem → for currentPID = 2 call Exit clean up (release resources) SP := SP + sizeof(Exit stack frame) ret ... (never here = rest of P.EXE main program) ... pop currentPID (1) ret goto

context switch to PID 2

context switch back to PID 1

1) Allocated memory (pages)2) CPU fault → kernel interrupt handler →

call procTable[currentPID].faultHandlers[faultID]3) Open files – e.g. ReadFile(fileDesc, ...):

read from procTable[currentPID].fileDescTable[fileDesc]

kernel initcall Exec(‘shell.exe’) load shell.exe call shell.exe entrypoint ... AllocMem → for currentPID = 1 repeat ... until key <> ENTER call Exec(‘P.EXE’) load P.EXE load & relocate EXE image load & relocate DLL images push currentPID (1) currentPID := AllocateNewPID; (2) call A.DLL entrypoint call B.DLL entrypoint call P.EXE entrypoint ... ... AllocMem → for currentPID = 2 call Exit clean up (release resources) SP := SP + sizeof(Exit stack frame) ret ... (never here = rest of P.EXE main program) ... pop currentPID (1) ret goto

context switch to PID 2

context switch back to PID 1

1) Allocated memory (pages)2) CPU fault → kernel interrupt handler →

call procTable[currentPID].faultHandlers[faultID]3) Open files – e.g. ReadFile(fileDesc, ...):

read from procTable[currentPID].fileDescTable[fileDesc]

4) Current path – e.g. OpenFile(path, ...)if path startsWith ‘/’ or ‘\’ then open file at (path)else open file at (procTable[currentPID].workingDir + path)

kernel initcall Exec(‘shell.exe’) load shell.exe call shell.exe entrypoint ... AllocMem → for currentPID = 1 repeat ... until key <> ENTER call Exec(‘P.EXE’) load P.EXE load & relocate EXE image load & relocate DLL images push currentPID (1) currentPID := AllocateNewPID; (2) call A.DLL entrypoint call B.DLL entrypoint call P.EXE entrypoint ... ... AllocMem → for currentPID = 2 call Exit clean up (release resources) SP := SP + sizeof(Exit stack frame) ret ... (never here = rest of P.EXE main program) ... pop currentPID (1) ret goto

context switch to PID 2

context switch back to PID 1

1) Allocated memory (pages)2) CPU fault → kernel interrupt handler →

call procTable[currentPID].faultHandlers[faultID]3) Open files – e.g. ReadFile(fileDesc, ...):

read from procTable[currentPID].fileDescTable[fileDesc]

4) Current path – e.g. OpenFile(path, ...)if path startsWith ‘/’ or ‘\’ then open file at (path)else open file at (procTable[currentPID].workingDir + path)

5) List of loaded DLLs

Further Options How to Take Advantage of Processes …

kernel initcall Exec(‘shell.exe’) load shell.exe call shell.exe entrypoint ... repeat ... until key <> ENTER call Exec(‘P.EXE’) load P.EXE load & relocate EXE image load & relocate DLL images push currentPID currentPID := AllocateNewPID; call A.DLL entrypoint call B.DLL entrypoint call P.EXE entrypoint ... ... call Exit clean up (release resources) SP := SP + sizeof(Exit stack frame) ret ... (never here = rest of P.EXE main program) ... pop currentPID ret goto

...

...shell’s entrypoint

argumentsreturn address

shell → kernelInitshell local & temporary

variables Exec syscall

argumentsreturn address

Exec → shellExec local & temporary

variablesP.EXE’s entrypoint

arguments

SP →return address

P main → Exec???SP →

P main local & temporary variables

Exit syscallarguments

return addressExit → P main

SP →Exit local & temporary

variables........................

kernel initcall Exec(‘shell.exe’) load shell.exe call shell.exe entrypoint ... repeat ... until key <> ENTER call Exec(‘P.EXE’) load P.EXE load & relocate EXE image load & relocate DLL images push currentPID currentPID := AllocateNewPID; call A.DLL entrypoint call B.DLL entrypoint call P.EXE entrypoint ... call f1 in P.EXE ... call f2 in P.EXE ... call Exit clean up (release resources) SP := SP + sizeof(Exit stack frame) ret ... (never here = rest of f2) ... ... (never here = rest of f1) ... pop currentPID ret goto

...

...shell’s entrypoint

argumentsreturn address

shell → kernelInit Exec syscall

argumentsreturn address

Exec → shellP.EXE’s entrypoint

argumentsreturn address

P main → Execf1 in P.EXE function

argumentsreturn addressf1 → P main

f2 in P.EXE functionarguments

return addressf2 → f1Exit syscallarguments

SP →return addressExit → f2

...

...

...

...IP

kernel initcall Exec(‘shell.exe’) load shell.exe call shell.exe entrypoint ... repeat ... until key <> ENTER call Exec(‘P.EXE’) load P.EXE load & relocate EXE image load & relocate DLL images push currentPID currentPID := AllocateNewPID; call A.DLL entrypoint call B.DLL entrypoint call P.EXE entrypoint ... call f1 in P.EXE ... call f2 in P.EXE ... call Exit clean up (release resources) SP := SP + sizeof(Exit stack frame) ret ... (never here = rest of f2) ... ... (never here = rest of f1) ... pop currentPID ret goto

...

...shell’s entrypoint

argumentsreturn address

shell → kernelInit Exec syscall

argumentsreturn address

Exec → shellP.EXE’s entrypoint

argumentsreturn address

P main → Execf1 in P.EXE function

argumentsreturn addressf1 → P main

f2 in P.EXE functionarguments

SP →return addressf2 → f1Exit syscallarguments

return addressExit → f2

...

...

...

...IP

kernel initcall Exec(‘shell.exe’) load shell.exe call shell.exe entrypoint ... repeat ... until key <> ENTER call Exec(‘P.EXE’) load P.EXE load & relocate EXE image load & relocate DLL images push currentPID currentPID := AllocateNewPID; call A.DLL entrypoint call B.DLL entrypoint call P.EXE entrypoint ... call f1 in P.EXE ... call f2 in P.EXE ... call Exit clean up (release resources) SP := SP + sizeof(Exit stack frame) ret ... (never here = rest of f2) ... f1 execution continues ... pop currentPID ret goto

...

...shell’s entrypoint

argumentsreturn address

shell → kernelInit Exec syscall

argumentsreturn address

Exec → shellP.EXE’s entrypoint

argumentsreturn address

P main → Execf1 in P.EXE function

argumentsreturn addressf1 → P main

SP →f2 in P.EXE function

argumentsreturn addressf2 → f1Exit syscallarguments

return addressExit → f2

...

...

...

...

IP

kernel initcall Exec(‘shell.exe’) load shell.exe call shell.exe entrypoint ... repeat ... until key <> ENTER call Exec(‘P.EXE’) load P.EXE load & relocate EXE image load & relocate DLL images push currentPID currentPID := AllocateNewPID; procTable[currentPID].oldSP := SP call A.DLL entrypoint call B.DLL entrypoint call P.EXE entrypoint ... call f1 in P.EXE ... call f2 in P.EXE ... call Exit clean up (release resources) SP := procTable[currentPID].oldSP ret ... (never here = rest of f2) ... ... (never here = rest of f1) ... pop currentPID ret goto

...

...shell’s entrypoint

argumentsreturn address

shell → kernelInit Exec syscall

argumentsreturn address

Exec → shellP.EXE’s entrypoint

argumentsreturn address

P main → Execf1 in P.EXE function

argumentsreturn addressf1 → P main

f2 in P.EXE functionarguments

return addressf2 → f1Exit syscallarguments

SP →return addressExit → f2

...

...

...

...IP

kernel initcall Exec(‘shell.exe’) load shell.exe call shell.exe entrypoint ... repeat ... until key <> ENTER call Exec(‘P.EXE’) load P.EXE load & relocate EXE image load & relocate DLL images push currentPID currentPID := AllocateNewPID; procTable[currentPID].oldSP := SP call A.DLL entrypoint call B.DLL entrypoint call P.EXE entrypoint ... call f1 in P.EXE ... call f2 in P.EXE ... call Exit clean up (release resources) SP := procTable[currentPID].oldSP ret ... (never here = rest of f2) ... ... (never here = rest of f1) ... pop currentPID ret goto

...

...shell’s entrypoint

argumentsreturn address

shell → kernelInit Exec syscall

arguments

SP →return address

Exec → shellP.EXE’s entrypoint

argumentsreturn address

P main → Execf1 in P.EXE function

argumentsreturn addressf1 → P main

f2 in P.EXE functionarguments

return addressf2 → f1Exit syscallarguments

return addressExit → f2

...

...

...

...IP

kernel initcall Exec(‘shell.exe’) load shell.exe call shell.exe entrypoint ... repeat ... until key <> ENTER call Exec(‘P.EXE’) load P.EXE load & relocate EXE image load & relocate DLL images push currentPID currentPID := AllocateNewPID; procTable[currentPID].oldSP := SP – sizeof(entrypoint’s stack frame) call A.DLL entrypoint call B.DLL entrypoint call P.EXE entrypoint ... call f1 in P.EXE ... call f2 in P.EXE ... call Exit clean up (release resources) SP := procTable[currentPID].oldSP ret ... (never here = rest of f2) ... ... (never here = rest of f1) ... pop currentPID ret goto

...

...shell’s entrypoint

argumentsreturn address

shell → kernelInit Exec syscall

argumentsreturn address

Exec → shellP.EXE’s entrypoint

argumentsreturn address

P main → Execf1 in P.EXE function

argumentsreturn addressf1 → P main

f2 in P.EXE functionarguments

return addressf2 → f1Exit syscallarguments

SP →return addressExit → f2

...

...

...

...IP

kernel initcall Exec(‘shell.exe’) load shell.exe call shell.exe entrypoint ... repeat ... until key <> ENTER call Exec(‘P.EXE’) load P.EXE load & relocate EXE image load & relocate DLL images push currentPID currentPID := AllocateNewPID; procTable[currentPID].oldSP := SP – sizeof(entrypoint’s stack frame) call A.DLL entrypoint call B.DLL entrypoint call P.EXE entrypoint ... call f1 in P.EXE ... call f2 in P.EXE ... call Exit clean up (release resources) SP := procTable[currentPID].oldSP ret ... (never here = rest of f2) ... ... (never here = rest of f1) ... pop currentPID ret goto

...

...shell’s entrypoint

argumentsreturn address

shell → kernelInit Exec syscall

argumentsreturn address

Exec → shellP.EXE’s entrypoint

arguments

SP →return address

P main → Execf1 in P.EXE function

argumentsreturn addressf1 → P main

f2 in P.EXE functionarguments

return addressf2 → f1Exit syscallarguments

return addressExit → f2

...

...

...

...IP

...

kerneldata

IVTproc table...

page tbl kernel code

kernel codestackstack

guard pagefreefreefreefreefreefreefreefreefreefreefreefreefreefreefreefreefreeA dataA code

PT ...

Non-presentKernel/SupervisorUser Read/OnlyUser Read/Write

...

kerneldata

IVTproc table...

page tbl kernel code

kernel codestackstack

guard pagefreefreefreefreefreefreefreefreefreefreefreefreefreefreefreefreeA heapA dataA code

PT ...

→ Pascal runtime’s call of syscall (OS API) AllocMem

Non-presentKernel/SupervisorUser Read/OnlyUser Read/Write

...

kerneldata

IVTproc table...

page tbl kernel code

kernel codestackstack

guard pagefreefreefreefreefreefreefreefreefreefreefreefreefreefreeA heapA heapA heapA dataA code

PT ...

Non-presentKernel/SupervisorUser Read/OnlyUser Read/Write

...

kerneldata

IVTproc table...

page tbl kernel code

kernel codestackstack

guard pagefreefreefreefreefreefreefreefreefreefreeB heapB dataB codeB codeA heapA heapA heapA dataA code

PT ...

Non-presentKernel/SupervisorUser Read/OnlyUser Read/Write

...

kerneldata

IVTproc table...

page tbl kernel code

kernel codestackstack

guard pagefreefreefreefreefreefreefreefreefreefreeB heapB dataB codeB codeA heapA heapA heapA dataA code

PT ...

Non-presentKernel/SupervisorUser Read/OnlyUser Read/Write

CPU (x86/IA-32)...

kerneldata

...proc tableB page tbl

A page tbl

kernel codekernel code

stackstack

guard pagefreefreefreefreefreefreefreefreefreefreeB heapB dataB codeB codeA heapA heapA heapA dataA code

A PT

... B PT

31 0EIP

31 0ESP

31 page table base 0CR3

Non-presentKernel/SupervisorUser Read/OnlyUser Read/Write

CPU (x86/IA-32)...

kerneldata

...proc tableB page tbl

A page tbl

kernel codekernel code

stackstack

guard pagefreefreefreefreefreefreefreefreefreefreeB heapB dataB codeB codeA heapA heapA heapA dataA code

A PT

... B PT

31 0EIP

31 0ESP

31 page table base 0CR3

Non-presentKernel/SupervisorUser Read/OnlyUser Read/Write

CPU (x86/IA-32)...

kerneldata

...proc tableB page tbl

A page tbl

kernel codekernel code

stackstack

guard pagefreefreefreefreefreefreefreefreefreefreeB heapB dataB codeB codeA heapA heapA heapA dataA code

A PT

... B PT

31 0EIP

31 0ESP

31 page table base 0CR3

Non-presentKernel/SupervisorUser Read/OnlyUser Read/Write

CPU (x86/IA-32)...

kerneldata

...proc tableB page tbl

A page tbl

kernel codekernel code

stackstack

guard pagefreefreefreefreefreefreefreefreefreefreeB heapB dataB codeB codeA heapA heapA heapA dataA code

A PT

... B PT

31 0EIP

31 0ESP

31 page table base 0CR3

Non-presentKernel/SupervisorUser Read/OnlyUser Read/Write

CPU (x86/IA-32)...

kerneldata

...proc tableB page tbl

A page tbl

kernel codekernel code

stackstack

guard pagefreefreefreefreefreefreefreefreefreefreeB heapB dataB codeB codeA heapA heapA heapA dataA code

A PT

... B PT

31 0EIP

31 0ESP

31 page table base 0CR3

Non-presentKernel/SupervisorUser Read/OnlyUser Read/Write

kernel initcall Exec(‘shell.exe’) load shell.exe call shell.exe entrypoint ... repeat ... until key <> ENTER call Exec(‘P.EXE’) load P.EXE load & relocate EXE image load & relocate DLL images push currentPID currentPID := AllocateNewPID; procTable[currentPID].pageTable := InitilizeNewPageTable; CR3 := procTable[currentPID].pageTable; procTable[currentPID].oldSP := SP – sizeof(entrypoint’s stack frame) call A.DLL entrypoint call B.DLL entrypoint call P.EXE entrypoint ... call f1 in P.EXE ... call f2 in P.EXE ... call Exit clean up (release resources) SP := procTable[currentPID].oldSP ret ... (never here = rest of f2) ... ... (never here = rest of f1) ... pop currentPID CR3 := procTable[currentPID].pageTable; ret goto

context switch back to PID 1

context switch to PID 2

context switch to PID 2

1) Allocated memory (pages)2) CPU fault → kernel interrupt handler

call procTable[currentPID].faultHandlers[faultID]3) Open files – e.g. ReadFile(fileDesc, ...):

read from procTable[currentPID].fdt[fileDesc]4) Current path – e.g. OpenFile(path, ...)

if path startsWith ‘/’ or ‘\’ then open file at (path)else open file at (procTable[currentPID].workingDir + path)

5) List of loaded DLLs6) Page table (state of the address space)

CPU (x86/IA-32)...

kerneldata

...proc tableB page tbl

A page tbl

kernel codekernel code

stackstack

guard pagefreefreefreefreefreefreefreefreefreefreeB heapB dataB codeB codeA heapA heapA heapA dataA code

A PT

... B PT

31 0EIP

31 0ESP

31 page table base 0CR3

Non-presentKernel/SupervisorUser Read/OnlyUser Read/Write

nil = address 0= pointer(0)

CPU (x86/IA-32)...

kerneldata

...proc tableB page tbl

A page tbl

kernel codekernel code

stackstack

guard pagefreefreefreefreefreefreefreefreefreefreeB heapB dataB codeB codeA heapA heapA heapA dataA code

A PT

page 0 B PT

31 0EIP

31 0ESP

31 page table base 0CR3

Non-presentKernel/SupervisorUser Read/OnlyUser Read/Write

nil = address 0= pointer(0)

How a Debugger Works?

Visual Studio 2015 CommunityVisual Studio 2015 Enterprise

google: mff dreamspark

...

...

...

...

... ...

...

...

...

...

...

...

... $01000000

...

...006A $00B9100C00B9101A68 $00B9100700B9105B68 $00B91002406A $00B91000...

push dword ptr [00B9105Bh]

push dword 40h

push dword ptr [00B9105Bh]

push dword 0

code and data of debugged application (=

debugee)

code and data of DEBUGGER

...

...

...

...

... ...

...

...

...

...

...

...

... $01000000

...

...006A $00B9100C00B9101A68 $00B9100700B9105B68 $00B91002406A $00B91000...

push dword ptr [00B9105Bh]

push dword 40h

push dword ptr [00B9105Bh]

push dword 0

code and data of debugged application (=

debugee)

code and data of DEBUGGER

...

...

...

...

... ...

...

...

...

...

...

...

... $01000000

...

...006A $00B9100C00B9101A68 $00B9100700B9105B68 $00B91002406A $00B91000...

push dword ptr [00B9105Bh]

push dword 40h

push dword ptr [00B9105Bh]

push dword 0

code and data of debugged application (=

debugee)

code and data of DEBUGGER

...

...

...

...

... ...

...

...

...

...

...

...

... $01000000

...

...006A $00B9100C00B9101A68 $00B9100700B9105B68 $00B91002406A $00B91000...

push dword ptr [00B9105Bh]

push dword 40h

push dword ptr [00B9105Bh]

push dword 0

code and data of debugged application (=

debugee)

code and data of DEBUGGER

...

...

...

...

... ...

...

...

...

...

...

...

... $01000000

...

...006A $00B9100C00B9101A68 $00B9100700B9105B68 $00B91002406A $00B91000...

push dword ptr [00B9105Bh]

push dword 40h

push dword ptr [00B9105Bh]

push dword 0

code and data of debugged application (=

debugee)

code and data of DEBUGGER

...

...

... 685B10B90068...

........................ $01000000......006A $00B9100C00B9101A68 $00B9100700B9105B68 $00B91002406A $00B91000...

push dword ptr [00B9105Bh]

push dword 40h

push dword ptr [00B9105Bh]

push dword 0

code and data of debugged application (=

debugee)

code and data of DEBUGGER

variable holding copy of original app’s code

...

...

... 685B10B90068... $0100FFF0

........................ $01000000......006A $00B9100C00B9101A01 $00B9100700FFF015FF $00B91002406A $00B91000...

push dword ptr [00B9105Bh]

push dword 40h

push dword ptr [00B9105Bh]

push dword 0

code and data of debugged application (=

debugee)

code and data of DEBUGGER

variable holding copy of original app’s codevariable address of debugger step function

call [0100FFF0h]

JMP to entrypoint

...

...

... 685B10B90068... $0100FFF0

........................ $01000000......006A $00B9100C00B9101A01 $00B9100700FFF015FF $00B91002406A $00B91000...

push dword ptr [00B9105Bh]

push dword 40h

push dword ptr [00B9105Bh]

push dword 0

code and data of debugged application (=

debugee)

code and data of DEBUGGER

variable holding copy of original app’s codevariable address of debugger step function

call [0100FFF0h]

JMP to entrypoint EIP

...

...

... 685B10B90068... $0100FFF0

........................ $01000000......006A $00B9100C00B9101A01 $00B9100700FFF015FF $00B91002406A $00B91000...

push dword ptr [00B9105Bh]

push dword 40h

push dword ptr [00B9105Bh]

push dword 0

code and data of debugged application (=

debugee)

code and data of DEBUGGER

variable holding copy of original app’s codevariable address of debugger step function

call [0100FFF0h]

JMP to entrypoint

EIP

...

...

... 685B10B90068... $0100FFF0

........................ $01000000......006A $00B9100C00B9101A01 $00B9100700FFF015FF $00B91002406A $00B91000...

Execute main debugger loop (Update/Draw cycle to display UI)

save state of application (e.g. push all registers to stack)

push dword ptr [00B9105Bh]

push dword 40h

push dword ptr [00B9105Bh]

push dword 0

code and data of debugged application (=

debugee)

code and data of DEBUGGER

variable holding copy of original app’s codevariable address of debugger step function

call [0100FFF0h]

JMP to entrypoint

EIP

...

...

... 685B10B90068... $0100FFF0

........................ $01000000......006A $00B9100C00B9101A01 $00B9100700FFF015FF $00B91002406A $00B91000...

Execute main debugger loop (Update/Draw cycle to display UI)

save state of application (e.g. push all registers to stack)

push dword ptr [00B9105Bh]

push dword 40h

push dword ptr [00B9105Bh]

push dword 0

code and data of debugged application (=

debugee)

code and data of DEBUGGER

variable holding copy of original app’s codevariable address of debugger step function

call [0100FFF0h]

JMP to entrypoint

EIP

...

...

... 685B10B90068... $0100FFF0

........................ $01000000......006A $00B9100C00B9101A68 $00B9100700B9105B68 $00B91002406A $00B91000...

Execute main debugger loop (Update/Draw cycle to display UI)

save state of application (e.g. push all registers to stack)

push dword ptr [00B9105Bh]

push dword 40h

push dword ptr [00B9105Bh]

push dword 0

code and data of debugged application (=

debugee)

code and data of DEBUGGER

variable holding copy of original app’s codevariable address of debugger step function

JMP to entrypoint

EIP

...

...

... 681A10B9006A... $0100FFF0

........................ $01000000......006A $00B9100C00B9101A68 $00B9100700B9105B68 $00B91002406A $00B91000...

Execute main debugger loop (Update/Draw cycle to display UI)

save state of application (e.g. push all registers to stack)

push dword ptr [00B9105Bh]

push dword 40h

push dword ptr [00B9105Bh]

push dword 0

code and data of debugged application (=

debugee)

code and data of DEBUGGER

variable holding copy of original app’s codevariable address of debugger step function

JMP to entrypoint

EIP

...

...

... 681A10B9006A... $0100FFF0

........................ $01000000......0001 $00B9100C00FFF015FF $00B9100700B9105B68 $00B91002406A $00B91000...

Execute main debugger loop (Update/Draw cycle to display UI)

save state of application (e.g. push all registers to stack)

push dword ptr [00B9105Bh]

push dword 40h

push dword ptr [00B9105Bh]

push dword 0

code and data of debugged application (=

debugee)

code and data of DEBUGGER

variable holding copy of original app’s codevariable address of debugger step function

JMP to entrypoint

EIP

call [0100FFF0h]

...

...

... 681A10B9006A... $0100FFF0

RET..................... $01000000......0001 $00B9100C00FFF015FF $00B9100700B9105B68 $00B91002406A $00B91000...

Execute main debugger loop (Update/Draw cycle to display UI)

save state of application (e.g. push all registers to stack)

push dword ptr [00B9105Bh]

push dword 40h

push dword ptr [00B9105Bh]

push dword 0

code and data of debugged application (=

debugee)

code and data of DEBUGGER

variable holding copy of original app’s codevariable address of debugger step function

JMP to entrypoint

EIP

call [0100FFF0h]

restore state of application & jump back

...

...

... 681A10B9006A... $0100FFF0

RET..................... $01000000......0001 $00B9100C00FFF015FF $00B9100700B9105B68 $00B91002406A $00B91000...

Execute main debugger loop (Update/Draw cycle to display UI)

save state of application (e.g. push all registers to stack)

push dword ptr [00B9105Bh]

push dword 40h

push dword ptr [00B9105Bh]

push dword 0

code and data of debugged application (=

debugee)

code and data of DEBUGGER

variable holding copy of original app’s codevariable address of debugger step function

JMP to entrypoint

call [0100FFF0h]

restore state of application & jump backEIP

...

...

... 681A10B9006A... $0100FFF0

RET..................... $01000000......0001 $00B9100C00FFF015FF $00B9100700B9105B68 $00B91002406A $00B91000...

Execute main debugger loop (Update/Draw cycle to display UI)

save state of application (e.g. push all registers to stack)

push dword ptr [00B9105Bh]

push dword 40h

push dword ptr [00B9105Bh]

push dword 0

code and data of debugged application (=

debugee)

code and data of DEBUGGER

variable holding copy of original app’s codevariable address of debugger step function

JMP to entrypoint

call [0100FFF0h]

restore state of application & jump back

EIP

...

...

... 681A10B9006A... $0100FFF0

RET..................... $01000000......0001 $00B9100C00FFF015FF $00B9100700B9105B68 $00B91002406A $00B91000...

Execute main debugger loop (Update/Draw cycle to display UI)

save state of application (e.g. push all registers to stack)

push dword ptr [00B9105Bh]

push dword 40h

push dword ptr [00B9105Bh]

push dword 0

code and data of debugged application (=

debugee)

code and data of DEBUGGER

variable holding copy of original app’s codevariable address of debugger step function

JMP to entrypoint

call [0100FFF0h]

restore state of application & jump back

EIP

...

...

... 681A10B9006A... $0100FFF0

RET..................... $01000000......0001 $00B9100C00FFF015FF $00B9100700B9105B68 $00B91002406A $00B91000...

Execute main debugger loop (Update/Draw cycle to display UI)

save state of application (e.g. push all registers to stack)

push dword ptr [00B9105Bh]

push dword 40h

push dword ptr [00B9105Bh]

push dword 0

code and data of debugged application (=

debugee)

code and data of DEBUGGER

variable holding copy of original app’s codevariable address of debugger step function

JMP to entrypoint

call [0100FFF0h]

restore state of application & jump back

EIP

...

...

... 681A10B9006A... $0100FFF0

RET..................... $01000000......0001 $00B9100C00FFF015FF $00B9100700B9105B68 $00B91002406A $00B91000...

Execute main debugger loop (Update/Draw cycle to display UI)

save state of application (e.g. push all registers to stack)

push dword ptr [00B9105Bh]

push dword 40h

push dword ptr [00B9105Bh]

push dword 0

code and data of debugged application (=

debugee)

code and data of DEBUGGER

variable holding copy of original app’s codevariable address of debugger step function

JMP to entrypoint

call [0100FFF0h]

restore state of application & jump back

EIP

Stepping in Higher Level Programming Language (e.g. Pascal)

A.pasC1C2C3

A.exeI1I2I3I4I5I6

Stepping in Higher Level Programming Language (e.g. Pascal)

A.pasC1C2C3

A.exeI1I2I3I4I5I6

Stepping in Higher Level Programming Language (e.g. Pascal)

A.pasC1C2C3

A.exeI1I2I3I4I5I6

Typical ISA Arithmetic Instructions

MIPS: a := b op cx86, 6502: a := a op b

6502 Registers (Accumulator Architecture)

7 0A

7 0X

7 0Y

0000 0001 7 0S

P

15 0PC

7 0

Load Value Into Register (6502)LDA #$xx

LDA $xxxx

A := xx

A := ($xxxx)^

Load Value Into AccumulatorLDA #$xx

LDA $xxxx

LDA $xxxx,X

LDA $xxxx,Y

LDA ($xx,X)

LDA ($xx),Y

A := xx

A := ($xxxx)^

A := ($xxxx + X)^

A := ($xxxx + Y)^

A := ( (^word($00xx + X))^)^

A := ( (^word($00xx))^ + Y)^

Load Value Into RegisterLDA #$xx

LDA $xxxx

LDA $xxxx,X

LDA $xxxx,Y

LDX imm/addr

LDY imm/addr

A := xx

A := ($xxxx)^

A := ($xxxx + X)^

A := ($xxxx + Y)^

X := imm/addr

X := imm/addr

& Store Value From RegisterLDA #$xx

LDA $xxxx

LDA $xxxx,X

LDA $xxxx,Y

LDX imm/addr

LDY imm/addr

STA $xxxx

STA $xxxx,X

STA $xxxx,Y

STX addr

STY addr

A := xx

A := ($xxxx)^

A := ($xxxx + X)^

A := ($xxxx + Y)^

X := imm/addr

X := imm/addr

($xxxx)^ := A

($xxxx + X)^ := A

($xxxx + Y)^ := A

addr := X

addr := Y

Move (Transfer) Value Between RegistersLDA #$xx

LDA $xxxx

LDA $xxxx,X

LDA $xxxx,Y

LDX imm/addr

LDY imm/addr

STA $xxxx

STA $xxxx,X

STA $xxxx,Y

STX addr

STY addr

A := xx

A := ($xxxx)^

A := ($xxxx + X)^

A := ($xxxx + Y)^

X := imm/addr

X := imm/addr

($xxxx)^ := A

($xxxx + X)^ := A

($xxxx + Y)^ := A

addr := X

addr := Y

TAX

TXA

TAY

TYA

TSX

TXS

X := A

A := X

Y := A

A := Y

X := S

S := X

Push To Stack & Pop (Pull) From Stack LDA #$xx

LDA $xxxx

LDA $xxxx,X

LDA $xxxx,Y

LDX imm/addr

LDY imm/addr

STA $xxxx

STA $xxxx,X

STA $xxxx,Y

STX addr

STY addr

A := xx

A := ($xxxx)^

A := ($xxxx + X)^

A := ($xxxx + Y)^

X := imm/addr

X := imm/addr

($xxxx)^ := A

($xxxx + X)^ := A

($xxxx + Y)^ := A

addr := X

addr := Y

TAX

TXA

TAY

TYA

TSX

TXS

X := A

A := X

Y := A

A := Y

X := S

S := X

PHP

PLP

PHA

PLA

push P (flags)

pop P (flags)

push A

pop A

Setting FlagsLDA #$xx

LDA $xxxx

LDA $xxxx,X

LDA $xxxx,Y

LDX imm/addr

LDY imm/addr

STA $xxxx

STA $xxxx,X

STA $xxxx,Y

STX addr

STY addr

A := xx

A := ($xxxx)^

A := ($xxxx + X)^

A := ($xxxx + Y)^

X := imm/addr

X := imm/addr

($xxxx)^ := A

($xxxx + X)^ := A

($xxxx + Y)^ := A

addr := X

addr := Y

TAX

TXA

TAY

TYA

TSX

TXS

X := A

A := X

Y := A

A := Y

X := S

S := X

PHP

PLP

PHA

PLA

push P (flags)

pop P (flags)

push A

pop A

P.Negative := target.7

if target = 0 then P.Zero := 1else P.Zero := 0;

P N... ..Z.7654 3210

Setting FlagsLDA #$xx

LDA $xxxx

LDA $xxxx,X

LDA $xxxx,Y

LDX imm/addr

LDY imm/addr

STA $xxxx

STA $xxxx,X

STA $xxxx,Y

STX addr

STY addr

A := xx

A := ($xxxx)^

A := ($xxxx + X)^

A := ($xxxx + Y)^

X := imm/addr

X := imm/addr

($xxxx)^ := A

($xxxx + X)^ := A

($xxxx + Y)^ := A

addr := X

addr := Y

TAX

TXA

TAY

TYA

TSX

TXS

X := A

A := X

Y := A

A := Y

X := S

S := X

PHP

PLP

PHA

PLA

push P (flags)

pop P (flags)

push A

pop A

P.Negative := target.7

if target = 0 then P.Zero := 1else P.Zero := 0;

CLC

SEC

P.Carry := 0

P.Carry := 1

P N... ..Z.7654 3210

Bitwise OperationsORA imm/addr

AND imm/addr

EOR imm/addr

? NOT

ASL A

LSR A

A := A BitwiseOr imm/addr

A := A BitwiseAnd imm/addr

A := A BitwiseXor imm/addr

EOR #$FF

A := A shl 1

A := A shr 1

P.Negative := A.7

if A = 0 then P.Zero := 1else P.Zero := 0;

Oring 16-bit Numbers (e.g. Little Endian)

A7 A6 A5 A4 A3 A2 A1 A0A15A14A13A12A11A10 A9 A8

LSB of A stored at $A000MSB of A stored at $A001

B7 B6 B5 B4 B3 B2 B1 B0B15B14B13B12B11B10 B9 B8

LSB of B stored at $B000MSB of B stored at $B001

or

=

C7 C6 C5 C4 C3 C2 C1 C0C15C14C13C12C11C10 C9 C8

LSB of C stored at $C000MSB of C stored at $C001

Oring 16-bit Numbers (e.g. Little Endian)

A7 A6 A5 A4 A3 A2 A1 A0A15A14A13A12A11A10 A9 A8

LSB of A stored at $A000MSB of A stored at $A001

B7 B6 B5 B4 B3 B2 B1 B0B15B14B13B12B11B10 B9 B8

LSB of B stored at $B000MSB of B stored at $B001

or

=

C7 C6 C5 C4 C3 C2 C1 C0C15C14C13C12C11C10 C9 C8

LSB of C stored at $C000MSB of C stored at $C001

or

=

LDA $A000ORA $B000STA $C000

LDA $A001ORA $B001STA $C001

result := A + imm/addr + P.CarryP.Carry := result.8A := result.7 … result.0

Integer OperationsADC imm/addr

P.Negative := A.7

if A = 0 then P.Zero := 1else P.Zero := 0;

P N... ..ZC7654 3210

result := A + imm/addr + P.CarryP.Carry := result.8A := result.7 … result.0

Integer Operations (Adding 8-bit Numbers)

ADC imm/addr

P.Negative := A.7

if A = 0 then P.Zero := 1else P.Zero := 0;

P N... ..ZC7654 3210

A7 A6 A5 A4 A3 A2 A1 A0

LSB of A stored at $A000

B7 B6 B5 B4 B3 B2 B1 B0

LSB of B stored at $B000+

=

C7 C6 C5 C4 C3 C2 C1 C0

LSB of C stored at $C000

C8carry

0carry

+

=

LDA $A000CLCADC $B000STA $C000

Adding 16-bit Numbers (e.g. Little Endian)

A7 A6 A5 A4 A3 A2 A1 A0A15A14A13A12A11A10 A9 A8

LSB of A stored at $A000MSB of A stored at $A001

B7 B6 B5 B4 B3 B2 B1 B0B15B14B13B12B11B10 B9 B8

LSB of B stored at $B000MSB of B stored at $B001

+

=

C7 C6 C5 C4 C3 C2 C1 C0C15C14C13C12C11C10 C9 C8

LSB of C stored at $C000MSB of C stored at $C001

result := A + imm/addr + P.CarryP.Carry := result.8A := result.7 … result.0

ADC imm/addr

P.Negative := A.7

if A = 0 then P.Zero := 1else P.Zero := 0;

result := A + imm/addr + P.CarryP.Carry := result.8A := result.7 … result.0

Adding 16-bit Numbers (e.g. Little Endian)ADC imm/addr

P.Negative := A.7

if A = 0 then P.Zero := 1else P.Zero := 0;

A7 A6 A5 A4 A3 A2 A1 A0

LSB of A stored at $A000

B7 B6 B5 B4 B3 B2 B1 B0

LSB of B stored at $B000+

=

C7 C6 C5 C4 C3 C2 C1 C0

LSB of C stored at $C000

C8carry

0carry

+

=

result := A + imm/addr + P.CarryP.Carry := result.8A := result.7 … result.0

Adding 16-bit Numbers (e.g. Little Endian)ADC imm/addr

P.Negative := A.7

if A = 0 then P.Zero := 1else P.Zero := 0;

A7 A6 A5 A4 A3 A2 A1 A0

LSB of A stored at $A000

B7 B6 B5 B4 B3 B2 B1 B0

LSB of B stored at $B000+

=

C7 C6 C5 C4 C3 C2 C1 C0

LSB of C stored at $C000

C8carry

0carry

+

=

LDA $A000CLCADC $B000STA $C000

result := A + imm/addr + P.CarryP.Carry := result.8A := result.7 … result.0

Adding 16-bit Numbers (e.g. Little Endian)ADC imm/addr

P.Negative := A.7

if A = 0 then P.Zero := 1else P.Zero := 0;

A7 A6 A5 A4 A3 A2 A1 A0

A15A14A13A12A11A10 A9 A8

LSB of A stored at $A000

MSB of A stored at $A001

B7 B6 B5 B4 B3 B2 B1 B0

B15B14B13B12B11B10 B9 B8

LSB of B stored at $B000

MSB of B stored at $B001

+

=

C7 C6 C5 C4 C3 C2 C1 C0

C15C14C13C12C11C10 C9 C8

LSB of C stored at $C000

MSB of C stored at $C001

C8carry

+

=

0carry

+

=

C16carry

=

LDA $A000CLCADC $B000STA $C000

+

result := A + imm/addr + P.CarryP.Carry := result.8A := result.7 … result.0

Adding 16-bit Numbers (e.g. Little Endian)ADC imm/addr

P.Negative := A.7

if A = 0 then P.Zero := 1else P.Zero := 0;

A7 A6 A5 A4 A3 A2 A1 A0

A15A14A13A12A11A10 A9 A8

LSB of A stored at $A000

MSB of A stored at $A001

B7 B6 B5 B4 B3 B2 B1 B0

B15B14B13B12B11B10 B9 B8

LSB of B stored at $B000

MSB of B stored at $B001

+

=

C7 C6 C5 C4 C3 C2 C1 C0

C15C14C13C12C11C10 C9 C8

LSB of C stored at $C000

MSB of C stored at $C001

C8carry

+

=

0carry

+

=

C16carry

=

LDA $A000CLCADC $B000STA $C000

LDA $A001ADC $B001STA $C001

+

Adding 16-bit Numbers (e.g. Little Endian)

LDA $A000CLCADC $B000STA $C000LDA $A001ADC $B001STA $C001

A7 A6 A5 A4 A3 A2 A1 A0A15A14A13A12A11A10 A9 A8

LSB of A stored at $A000MSB of A stored at $A001

B7 B6 B5 B4 B3 B2 B1 B0B15B14B13B12B11B10 B9 B8

LSB of B stored at $B000MSB of B stored at $B001

+

=

C7 C6 C5 C4 C3 C2 C1 C0C15C14C13C12C11C10 C9 C8

LSB of C stored at $C000MSB of C stored at $C001

result := A + imm/addr + P.CarryP.Carry := result.8A := result.7 … result.0

ADC imm/addr

P.Negative := A.7

if A = 0 then P.Zero := 1else P.Zero := 0;

Integer Operations – Subtraction? Via Two’s Complement

ADC imm/addr result := A + imm/addr + P.CarryP.Carry := result.8A := result.7 … result.0

P.Negative := A.7

if A = 0 then P.Zero := 1else P.Zero := 0;

A := value – A↓INC ANOT AADD value

A := value – A↓CLCADC #1EOR #$FFCLCADC value

Integer Operations – Subtraction? Subtract with Borrow

ADC imm/addr

SBC imm/addr

result := A + imm/addr + P.CarryP.Carry := result.8A := result.7 … result.0

result := A – imm/addr – not(P.Carry)P.Carry := not(result.7)A := result.7 … result.0

P.Negative := A.7

if A = 0 then P.Zero := 1else P.Zero := 0;

P.Negative := A.7

if A = 0 then P.Zero := 1else P.Zero := 0;

Other Integer Operations

ADC imm/addr

SBC imm/addr

INXINYDEXDEY

result := A + imm/addr + P.CarryP.Carry := result.8A := result.7 … result.0

result := A – imm/addr – not(P.Carry)P.Carry := not(result.7)A := result.7 … result.0

X := X + 1Y := Y + 1X := X – 1Y := Y - 1

P.Negative := A.7

if A = 0 then P.Zero := 1else P.Zero := 0;

P.Negative := A.7

if A = 0 then P.Zero := 1else P.Zero := 0;

P.Negative := X/Y.7

if X/Y = 0 then P.Zero := 1else P.Zero := 0;