class-sep23-JL-final - Carnegie Mellon Basics of...

Carnegie Mellon
1
Basics of Machine-Level Programming
(continued)
Janne Lindqvist
(Slides adapted from Bryant, O’Hallaron, and Nath.)

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Carnegie Mellon
Today

Simple addressing modes continued

Complete addressing mode, address computation (leal)

Arithmetic operations

Intro to x86-64

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Simple Memory Addressing Modes

Normal (R) Mem[Reg[R]]
§
Register R specifies memory address
movl (%ecx),%eax

Displacement D(R) Mem[Reg[R]+D]
§
Register R specifies start of memory region
§
Constant displacement D specifies offset
movl 8(%ebp),%edx

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4
Using Simple Addressing Modes
void swap(int *xp, int *yp)
{
int t0 = *xp;
int t1 = *yp;
*xp = t1;
*yp = t0;
}
Body
Set
Up
Finish
swap:
pushl %ebp
movl %esp,%ebp
pushl %ebx
movl 8(%ebp), %edx
movl 12(%ebp), %ecx
movl (%edx), %ebx
movl (%ecx), %eax
movl %eax, (%edx)
movl %ebx, (%ecx)
popl %ebx
popl %ebp
ret

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5
CPU
Assembly Programmer’s View

Programmer-Visible State
§
PC: Program counter
§
Address of next instruction
§
Called “EIP” (IA32) or “RIP” (x86-64)
§
Register file
§
Heavily used program data
§
Condition codes
§
Store status information about most
recent arithmetic operation
§
Used for conditional branching
PC
Registers
Memory
Object Code
Program Data
OS Data
Addresses
Data
Instructions
Stack
Condition
Codes
§
Memory
§
Byte addressable array
§
Code, user data, (some) OS data
§
Includes stack used to support
procedures

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Using Simple Addressing Modes
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 8(%ebp), %edx
movl 12(%ebp), %ecx
movl (%edx), %ebx
movl (%ecx), %eax
movl %eax, (%edx)
movl %ebx, (%ecx)
popl %ebx
popl %ebp
ret
Body
Set
Up
Finish

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7
Understanding Swap
void swap(int *xp, int *yp)
{
int t0 = *xp;
int t1 = *yp;
*xp = t1;
*yp = t0;
}
Stack
(in memory)
Register Value
%edx xp
%ecx yp
%ebx t0
%eax t1
yp
xp
Rtn adr
Old % ebp
%ebp
0
4
8
12
Offset
•
•
•
Old % ebx -4
%esp
movl 8(%ebp), %edx # edx = xp
movl 12(%ebp), %ecx # ecx = yp
movl (%edx), %ebx # ebx = *xp (t0)
movl (%ecx), %eax # eax = *yp (t1)
movl %eax, (%edx) # *xp = t1
movl %ebx, (%ecx) # *yp = t0

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Understanding Swap
0x120
0x124
Rtn adr
%ebp
0
4
8
12
Offset
-4
123
456
Address
0x124
0x120
0x11c
0x118
0x114
0x110
0x10c
0x108
0x104
0x100
yp
xp
%eax
%edx
%ecx
%ebx
%esi
%edi
%esp
%ebp 0x104
movl 8(%ebp), %edx # edx = xp
movl 12(%ebp), %ecx # ecx = yp
movl (%edx), %ebx # ebx = *xp (t0)
movl (%ecx), %eax # eax = *yp (t1)
movl %eax, (%edx) # *xp = t1
movl %ebx, (%ecx) # *yp = t0

Carnegie Mellon
9
Understanding Swap
0x120
0x124
Rtn adr
%ebp
0
4
8
12
Offset
-4
123
456
Address
0x124
0x120
0x11c
0x118
0x114
0x110
0x10c
0x108
0x104
0x100
yp
xp
%eax
%edx
%ecx
%ebx
%esi
%edi
%esp
%ebp
0x124
0x104
movl 8(%ebp), %edx # edx = xp
movl 12(%ebp), %ecx # ecx = yp
movl (%edx), %ebx # ebx = *xp (t0)
movl (%ecx), %eax # eax = *yp (t1)
movl %eax, (%edx) # *xp = t1
movl %ebx, (%ecx) # *yp = t0

Carnegie Mellon
10
Understanding Swap
0x120
0x124
Rtn adr
%ebp
0
4
8
12
Offset
-4
123
456
Address
0x124
0x120
0x11c
0x118
0x114
0x110
0x10c
0x108
0x104
0x100
yp
xp
%eax
%edx
%ecx
%ebx
%esi
%edi
%esp
%ebp
0x120
0x104
0x124
movl 8(%ebp), %edx # edx = xp
movl 12(%ebp), %ecx # ecx = yp
movl (%edx), %ebx # ebx = *xp (t0)
movl (%ecx), %eax # eax = *yp (t1)
movl %eax, (%edx) # *xp = t1
movl %ebx, (%ecx) # *yp = t0

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456