04 linux stack frames 14 11 tủ tài liệu bách khoa

University of Washington Section 5: Procedures & Stacks          Stacks in memory and stack operations The stack used to keep track of procedure calls Return addresses and return values Stack-based languages The Linux stack frame Passing arguments on the stack Allocating local variables on the stack Register-saving conventions Procedures and stacks on x64 architecture Linux Stack Frame University of Washington IA32/Linux Stack Frame  Current Stack Frame (“Top” to Bottom)  “Argument build” area (parameters for function about to be called)  Local variables (if can’t be kept in registers)  Saved register context (when reusing registers)  Old frame pointer (for caller)  Caller Frame Arguments Frame pointer %ebp Saved Registers + Local Variables Caller’s Stack Frame  Return address Pushed by call instruction  Arguments for this call Return Addr Old %ebp  Linux Stack Frame Stack pointer %esp Argument Build University of Washington Revisiting swap int zip1 = 15213; int zip2 = 98195; void call_swap() { swap(&zip1, &zip2); } void swap(int *xp, int *yp) { int t0 = *xp; int t1 = *yp; *xp = t1; *yp = t0; } Linux Stack Frame University of Washington Revisiting swap Calling swap from call_swap int zip1 = 15213; int zip2 = 98195; call_swap: • • • pushl $zip2 pushl $zip1 call swap • • • void call_swap() { swap(&zip1, &zip2); } void swap(int *xp, int *yp) { int t0 = *xp; int t1 = *yp; *xp = t1; *yp = t0; } Linux Stack Frame # Global Var # Global Var University of Washington Revisiting swap Calling swap from call_swap int zip1 = 15213; int zip2 = 98195; call_swap: • • • pushl $zip2 pushl $zip1 call swap • • • void call_swap() { swap(&zip1, &zip2); } void swap(int *xp, int *yp) { int t0 = *xp; int t1 = *yp; *xp = t1; *yp = t0; } Linux Stack Frame • • • # Global Var # Global Var Resulting Stack &zip2 &zip1 Rtn adr %esp University of Washington Revisiting swap void swap(int *xp, int *yp) { int t0 = *xp; int t1 = *yp; *xp = t1; *yp = t0; } swap: pushl %ebp movl %esp,%ebp pushl %ebx movl movl movl movl movl movl 12(%ebp),%ecx 8(%ebp),%edx (%ecx),%eax (%edx),%ebx %eax,(%edx) %ebx,(%ecx) movl -4(%ebp),%ebx movl %ebp,%esp popl %ebp ret Linux Stack Frame Set Up Body Finish University of Washington swap Setup #1 Entering Stack Resulting Stack? %ebp • • • &zip2 &zip1 Rtn adr %esp swap: pushl %ebp movl %esp,%ebp pushl %ebx Linux Stack Frame University of Washington swap Setup #1 Entering Stack Resulting Stack %ebp %ebp • • • • • • &zip2 yp &zip1 xp Rtn adr %esp Rtn adr Old %ebp swap: pushl %ebp movl %esp,%ebp pushl %ebx Linux Stack Frame %esp University of Washington swap Setup #2 Entering Stack Resulting Stack %ebp • • • • • • &zip2 yp &zip1 xp Rtn adr %esp Rtn adr Old %ebp swap: pushl %ebp movl %esp,%ebp pushl %ebx Linux Stack Frame %ebp %esp University of Washington swap Setup #3 Entering Stack Resulting Stack %ebp • • • • • • &zip2 yp &zip1 xp Rtn adr %esp Rtn adr swap: pushl %ebp movl %esp,%ebp pushl %ebx Linux Stack Frame Old %ebp %ebp Old %ebx %esp University of Washington swap Body Entering Stack Resulting Stack %ebp • • • Offset relative to new %ebp 12 &zip2 &zip1 Rtn adr %esp movl 12(%ebp),%ecx movl 8(%ebp),%edx # get yp # get xp Linux Stack Frame • • • yp xp Rtn adr Old %ebp %ebp Old %ebx %esp University of Washington swap Finish #1 swap’s Stack Resulting Stack? • • • yp xp Rtn adr Old %ebp %ebp Old %ebx %esp movl -4(%ebp),%ebx movl %ebp,%esp popl %ebp ret Linux Stack Frame University of Washington swap Finish #1 swap’s Stack Resulting Stack • • • • • • yp yp xp xp Rtn adr Rtn adr Old %ebp %ebp Old %ebp %ebp Old %ebx %esp Old %ebx %esp movl -4(%ebp),%ebx movl %ebp,%esp popl %ebp ret Observation: Saved and restored register %ebx Linux Stack Frame University of Washington swap Finish #2 swap’s Stack Resulting Stack • • • • • • yp yp xp xp Rtn adr Rtn adr Old %ebp %ebp Old %ebx %esp Old %ebp movl -4(%ebp),%ebx movl %ebp,%esp popl %ebp ret Linux Stack Frame %ebp %esp University of Washington swap Finish #3 swap’s Stack Resulting Stack %ebp • • • • • • yp yp xp xp Rtn adr Rtn adr Old %ebp %ebp Old %ebx %esp movl -4(%ebp),%ebx movl %ebp,%esp popl %ebp ret Linux Stack Frame %esp University of Washington swap Finish #4 swap’s Stack Resulting Stack %ebp • • • • • • yp yp xp xp Rtn adr Old %ebp %ebp Old %ebx %esp movl -4(%ebp),%ebx movl %ebp,%esp popl %ebp ret Linux Stack Frame %esp University of Washington Disassembled swap 080483a4 : 80483a4: 55 80483a5: 89 e5 80483a7: 53 80483a8: 8b 55 08 80483ab: 8b 4d 0c 80483ae: 8b 1a 80483b0: 8b 01 80483b2: 89 02 80483b4: 89 19 80483b6: 5b 80483b7: c9 80483b8: c3 push mov push mov mov mov mov mov mov pop leave ret %ebp %esp,%ebp %ebx 0x8(%ebp),%edx 0xc(%ebp),%ecx (%edx),%ebx (%ecx),%eax %eax,(%edx) %ebx,(%ecx) %ebx mov pop %ebp,%esp %ebp Calling Code 8048409: 804840e: e8 96 ff ff ff 8b 45 f8 call 80483a4 mov 0xfffffff8(%ebp),%eax Linux Stack Frame University of Washington swap Finish #4 swap’s Stack Resulting Stack %ebp • • • • • • yp yp xp xp %esp Rtn adr Old %ebp %ebp Old %ebx %esp  movl -4(%ebp),%ebx movl %ebp,%esp popl %ebp ret Observation  Saved & restored register %ebx  Didn’t so for %eax, %ecx, or %edx Linux Stack Frame