115-410, F’11
Stack Discipline
Aug. 31, 2011
Dave Eckhardt
Dave Eckhardt
Slides originally stolen from 15-213
Slides originally stolen from 15-213
15-410
“An Experience Like No Other”
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Stack Discipline, Lecture Slide - Computer Science, Slides of Computers and Information technologies
Process Memory Model, IA32 stack organization, Register Saving conventions, Before and After main(), Project
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2010/2011
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Stack Discipline
Aug. 31, 2011
Dave Eckhardt Dave Eckhardt
Slides originally stolen from 15-213 Slides originally stolen from 15-
“An Experience Like No Other”
Synchronization
Registration Registration
If you're here but not registered, see me before noon
The wait list will probably be done today or tomorrow
(^) If I have asked you for data, please provide it!
If you haven't taken 15-213 (A/B, malloc lab ok) If you haven't taken 15-213 (A/B, malloc lab ok)
Contact me no later than today
Mid-Term Exam Mid-Term Exam
Two plausible days
When I ask you to fill out the web form, please do so promptly
Why Only 32?
You may have learned x86-64 aka EMT64 aka AMD64 You may have learned x86-64 aka EMT64 aka AMD
x86-64 is simpler than x86(-32) for user program code
(^) Lots of registers, registers more orthogonal
Why will 410 be x86 / IA32? Why will 410 be x86 / IA32?
x86-64 is not simpler for kernel code
(^) Machine begins in 16-bit mode, then 32, finally 64 » You don't have time to write 32 ⇒ 64 transition code » If we gave it to you, it would be a^ big^ black box
x86-64 is not simpler during debugging
(^) More registers means more registers to have wrong values
x86-64 virtual memory is a bit of a drag
(^) More steps than x86-32, but not more intellectually stimulating
There are still a lot of 32-bit machines in the world
(^) ...which can boot and run your personal OS
Private Address Spaces
Each process has its own private address space. Each process has its own private address space.
kernel virtual memory (code, data, heap, stack) memory mapped region for shared libraries run-time heap (managed by malloc) user stack (created at runtime) unused 0 %esp (stack pointer) memory invisible to user code brk 0xc 0x 0x read/write segments (.data, .bss) read-only segments (.init, .text, .rodata) loaded from the executable file 0xffffffff
Warning: Warning:
numbers numbers
specific to specific to
Linux 2.x Linux 2.x
on IA32!! on IA32!!
Warning: Warning:
details vary details vary
by OS and by OS and
kernel kernel
version! version!
Linux Memory Allocation
Linked
BF
7F
3F
Stack Libraries Text Data 08
Some
Heap
BF
7F
3F
Stack Libraries Text Data Heap 08
More
Heap
BF
7F
3F
Stack Libraries Text Data Heap Heap 08
Initially
BF
7F
3F
Stack Text Data 08
IA32 Stack
Region of memory managed
with stack discipline
“Grows” toward lower
addresses
Register %esp indicates
lowest stack address
(^) address of “top” element (^) stack pointer Stack Pointer %esp Stack Grows Down Increasing Addresses Stack “Top” Stack “Bottom”
IA32 Stack Popping
Popping Popping
popl Dest
Read memory at address
given by %esp
Increment %esp by 4
Store into Dest operand
Stack Pointer %esp Stack Grows Down Increasing Addresses Stack “Top” Stack “Bottom” +
%esp %eax %edx %esp %eax %edx %esp %eax %edx 0x 555 0x 0x 0x10c 0x 0x 555
Stack Operation Examples
0x 0x10c 0x 555
0x108 0x pushl %eax 0x 0x10c 0x 213
0x
popl %edx 0x
%esp %eip %esp %eip 0x804854e 0x 0x 0x10c 0x 0x 0x804854e 0x
Procedure Call Example
0x 0x10c 0x 123 0x call 8048b 804854e: e8 3d 06 00 00 call 8048b90
%esp %eip 0x %esp 0x8048591 %eip 0x 0x104 0x 0x 0x10c 0x 0x
Procedure Return Example
0x 0x10c 0x 123 ret 8048591: c3 ret 0x %eip is program counter 0x 0x
Call Chain Example
Code Structure Code Structure
yoo(…) {
who();
} who(…) {
- • • amI();
- • • amI();
- • • } amI(…) {
amI();
} yoo who amI amI amI
Call Chain
Procedure amI()
recursive
amI
Stack Pointer %esp yoo who proc Frame Pointer %ebp Stack “Top”
Stack Frames
Contents Contents
Local variables
Return information
Temporary space
Management Management
Space allocated when enter
procedure
(^) “Set-up” code
Deallocated when return
(^) “Finish” code
Pointers Pointers
Stack pointer %esp indicates
stack top
Frame pointer %ebp indicates
start of current frame
amI
swap()
void swap(int *xp, int *yp) { int t0 = *xp; int t1 = *yp; *xp = t1; *yp = t0; } int zip1 = 15213; int zip2 = 91125; void call_swap() { swap(&zip1, &zip2); } call_swap:
- • • pushl $zip2 # Global var pushl $zip1 # Global var call swap
- • • &zip &zip Rtn adr %esp
Resulting
Stack
Calling swap from call_swap
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 12(%ebp),%ecx movl 8(%ebp),%edx movl (%ecx),%eax movl (%edx),%ebx movl %eax,(%edx) movl %ebx,(%ecx) movl -4(%ebp),%ebx movl %ebp,%esp popl %ebp ret Body Set Up Finish Core