Node structure used in the linked list examples

struct Node definition used in using ARM assembler programming examples:

struct Node { int value1; // Data field 1 offset = 0 short value2; // Data field 2 offset = 4 short value3; // Data field 3 offset = 6 struct Node *next; // Link field offset = 8 }

Background information:

In order to show you how to access data field in a linked list, I will need to create a linked list...
List objects (= nodes) are created with the malloc( ) function
For simplicity, I will create a linked list using assembler directives inside the .data section

Creating a linked list using assembler directives

How I created a linked list using assembler directives:

Example of a linked list with 5 nodes:

p0: .4byte 333 // Object [333,23,33,p2] .2byte 23, 33 .4byte p2 .skip 4 // gap p1: .4byte 111 // Object [111,21,31,p3] .2byte 21, 31 .4byte p3 p2: .4byte 444 // Object [444,24,34,p4] .2byte 24, 34 .4byte p4 .skip 4 // gap p3: .4byte 222 // Object [222,22,32,p0] .2byte 22, 32 .4byte p0 .skip 4 // gap p4: .4byte 555 // Object [555,25,35,null] .2byte 25, 35 .4byte 0 // 0 = null head: .4byte p1

The first list element (= node) is p1 !! (Can you see it ?)

Creating a linked list using assembler directives

The assembler directives created the following linked list:

head ⇒ [111,21,31,•]⇒[222,22,32,•] ⇒[333,23,33,•]⇒[444,24,34,•]⇒[555,25,35,null]

p0: .4byte 333 // Object [333,23,33,p2] .2byte 23, 33 .4byte p2 .skip 4 // gap p1: .4byte 111 // Object [111,21,31,p3] .2byte 21, 31 .4byte p3 p2: .4byte 444 // Object [444,24,34,p4] .2byte 24, 34 .4byte p4 .skip 4 // gap p3: .4byte 222 // Object [222,22,32,p0] .2byte 22, 32 .4byte p0 .skip 4 // gap p4: .4byte 555 // Object [555,25,35,null] .2byte 25, 35 .4byte 0 // 0 = null head: .4byte p1 // head contains address p1

DEMO: /home/cs255001/demo/asm/4-linked-list/demo2.s

Review: how to calculate the offset of fields in a (list) object - Example 2

Given the following struct Node (object) definition:

struct Node { int value1; // Data field 1 short value2; // Data field 2 short value3; // Data field 3 List next; // Link field };

The offset of the fields in objects defined by the above class definition are:

Offset(value1) = 0 Offset(value2) = 4 Offset(value3) = 6 (4+2) Offset(next) = 8 (4+2+2)

We now discuss how to access a list element using ARM assembler code

Linked list access example 1: load data fields in the first object in the list into registers R1, R2, R3

Write ARM assembler code to:

load (= fetch) head.value1,value2,value3 into registers R1, R2, R3, respectively

ARM assembler instructions: // Fetch: head.value1, 2 and 3

DEMO: /home/cs255001/demo/asm/4-linked-list/demo2.s

Linked list access example 1: load data fields in the first object in the list into registers R1, R2, R3

The variables value1, value2 and value3 are fetched using load instructions with their corresponding offsets:

ARM assembler instructions: // Fetch: head.value1, 2 and 3 // Preparation: // r0 = base address ldr r1, [r0, #0]//Offset(v1)=0 ldrsh r2, [r0, #4]//Offset(v2)=4 ldrsh r3, [r0, #6]//Offset(v3)=6

Required preparation : r0 = base address of the first Node "object" (struct)

Linked list access example 1: load data fields in the first object in the list into registers R1, R2, R3

The variable head contains the base address of the first Node "object" (struct):

ARM assembler instructions: // Fetch: head.value1, 2 and 3 // Preparation: // r0 = head ldr r1, [r0, #0]//Offset(v1)=0 ldrsh r2, [r0, #4]//Offset(v2)=4 ldrsh r3, [r0, #6]//Offset(v3)=6

DEMO: /home/cs255001/demo/asm/4-linked-list/demo2.s

Linked list access example 1: load data fields in the first object in the list into registers R1, R2, R3

Solution: assembler code to load (= fetch) head.value1,value2,value3 into registers R1, R2, R3:

ARM assembler instructions: // Fetch: head.value1, 2 and 3 movw r0, #:lower16:head movt r0, #:upper16:head ldr r0, [r0] // R0 = head ldr r1, [r0, #0]//Offset(v1)=0 ldrsh r2, [r0, #4]//Offset(v2)=4 ldrsh r3, [r0, #6]//Offset(v3)=6

DEMO: /home/cs255001/demo/asm/4-linked-list/demo2.s

Linked list access example 2: load data fields in the 2nd object in the list into registers R1, R2, R3

Write assembler code to:

load (= fetch) head.next.value1,value2,value3 into registers R1, R2, R3, respectively

ARM assembler instructions: // Fetch: head.next.val1, 2 and 3

DEMO: /home/cs255001/demo/asm/4-linked-list/demo2.s

Linked list access example 2: load data fields in the 2nd object in the list into registers R1, R2, R3

The variables value1, value2 and value3 are fetched using load instructions with their corresponding offsets:

ARM assembler instructions: // Fetch: head.next.val1, 2 and 3 // Preparation: // r0 = base address ldr r1, [r0, #0]//Offset(v1)=0 ldrsh r2, [r0, #4]//Offset(v2)=4 ldrsh r3, [r0, #6]//Offset(v3)=6

Required preparation : r0 = base address of the 2nd Node "object" (struct)

Linked list access example 2: load data fields in the 2nd object in the list into registers R1, R2, R3

The base address of the 2nd list object is stored in the variable head.next:

ARM assembler instructions: // Fetch: head.next.val1, 2 and 3 // Preparation: // r0 = head.next ldr r1, [r0, #0]//Offset(v1)=0 ldrsh r2, [r0, #4]//Offset(v2)=4 ldrsh r3, [r0, #6]//Offset(v3)=6

DEMO: /home/cs255001/demo/asm/4-linked-list/demo2.s

Linked list access example 2: load data fields in the 2nd object in the list into registers R1, R2, R3

We must start by fetching head in register R0:

ARM assembler instructions: // Fetch: head.next.val1, 2 and 3 // Preparation: // r0 = head.next movw r0, #:lower16:head movt r0, #:upper16:head ldr r0, [r0] // r0=head ldr r1, [r0, #0]//Offset(v1)=0 ldrsh r2, [r0, #4]//Offset(v2)=4 ldrsh r3, [r0, #6]//Offset(v3)=6

Then: use R0 to fetch head.next (next has offset=8) into R0 !!!

Linked list access example 2: load data fields in the 2nd object in the list into registers R1, R2, R3

Complete solution: assembler code to load (= fetch) head.value1,value2,value3 into registers R1, R2, R3:

ARM assembler instructions: // Fetch: head.next.val1, 2 and 3 // Preparation: // r0 = head.next movw r0, #:lower16:head movt r0, #:upper16:head ldr r0, [r0] // r0=head ldr r0, [r0,#8] // r0=head.next ldr r1, [r0, #0]//Offset(v1)=0 ldrsh r2, [r0, #4]//Offset(v2)=4 ldrsh r3, [r0, #6]//Offset(v3)=6

DEMO: /home/cs255001/demo/asm/4-linked-list/demo2.s

Linked list example without pictures....

Fetch the following variable into register R1:

r1 = head.next.next.value2

Solution:

DEMO: /home/cs255001/demo/asm/4-linked-list/demo2.s

Linked list example without pictures....

Fetch the following variable into register R1:

r1 = head.next.next.value2

Solution:

movw r0, #:lower16:head movt r0, #:upper16:head ldr r0, [r0] // r0 = head

DEMO: /home/cs255001/demo/asm/4-linked-list/demo2.s

Linked list example without pictures....

Fetch the following variable into register R1:

r1 = head.next.next.value2

Solution:

movw r0, #:lower16:head movt r0, #:upper16:head ldr r0, [r0] // r0 = head ldr r0, [r0, #8] // r0 = head.next

DEMO: /home/cs255001/demo/asm/4-linked-list/demo2.s

Linked list example without pictures....

Fetch the following variable into register R1:

r1 = head.next.next.value2

Solution:

movw r0, #:lower16:head movt r0, #:upper16:head ldr r0, [r0] // r0 = head ldr r0, [r0, #8] // r0 = head.next ldr r0, [r0, #8] // r0 = head.next.next // We now have: r0 = base address of the required list object

DEMO: /home/cs255001/demo/asm/4-linked-list/demo2.s

Linked list example without pictures....

Fetch the following variable into register R1:

r1 = head.next.next.value2

Solution:

movw r0, #:lower16:head movt r0, #:upper16:head ldr r0, [r0] // r0 = head ldr r0, [r0, #8] // r0 = head.next ldr r0, [r0, #8] // r0 = head.next.next ldrsh r1, [r0, #4] // r1 = head.next.next.value2

DEMO: /home/cs255001/demo/asm/4-linked-list/demo2.s

Assignment example with linked list

Translate the following assignment statement into ARM assembler:

head.next.next.value2 = 99;

Solution:

DEMO: /home/cs255001/demo/asm/4-linked-list/demo2.s

Assignment example with linked list

Translate the following assignment statement into ARM assembler:

head.next.next.value2 = 99;

Solution:

// Get the RHS first mov r0, #99 // r0 = 99

DEMO: /home/cs255001/demo/asm/4-linked-list/demo2.s

Assignment example with linked list

Translate the following assignment statement into ARM assembler:

head.next.next.value2 = 99;

Solution:

// Get the RHS first mov r0, #99 // r0 = 99 // Preparation: base address r1 = head.next.next

DEMO: /home/cs255001/demo/asm/4-linked-list/demo2.s

Assignment example with linked list

Translate the following assignment statement into ARM assembler:

head.next.next.value2 = 99;

Solution:

// Get the RHS first mov r0, #99 // r0 = 99 // Preparation: base address r1 = head.next.next movw r1, #:lower16:head movt r1, #:upper16:head // r1 = addr(head) ldr r1, [r1] // r1 = head

DEMO: /home/cs255001/demo/asm/4-linked-list/demo2.s

Assignment example with linked list

Translate the following assignment statement into ARM assembler:

head.next.next.value2 = 99;

Solution:

// Get the RHS first mov r0, #99 // r0 = 99 // Preparation: base address r1 = head.next.next movw r1, #:lower16:head movt r1, #:upper16:head // r1 = addr(head) ldr r1, [r1] // r1 = head ldr r1, [r1, #8] // r1 = head.next

DEMO: /home/cs255001/demo/asm/4-linked-list/demo2.s

Assignment example with linked list

Translate the following assignment statement into ARM assembler:

head.next.next.value2 = 99;

Solution:

// Get the RHS first mov r0, #99 // r0 = 99 // Preparation: base address r1 = head.next.next movw r1, #:lower16:head movt r1, #:upper16:head // r1 = addr(head) ldr r1, [r1] // r1 = head ldr r1, [r1, #8] // r1 = head.next ldr r1, [r1, #8] // r1 = head.next.next // We now have: r1 = base address of the required list object

DEMO: /home/cs255001/demo/asm/4-linked-list/demo2.s

Assignment example with linked list

Translate the following assignment statement into ARM assembler:

head.next.next.value2 = 99;

Solution:

// Get the RHS first mov r0, #99 // r0 = 99 // Preparation: base address r1 = head.next.next - DONE ! movw r1, #:lower16:head movt r1, #:upper16:head // r1 = addr(head) ldr r1, [r1] // r1 = head ldr r1, [r1, #8] // r1 = head.next ldr r1, [r1, #8] // r1 = head.next.next strh r0, [r1, #4] // Offset(value2) = 4

DEMO: /home/cs255001/demo/asm/4-linked-list/demo2.s

Assignment example with linked list

Translate the following assignment statement into ARM assembler:

head.value1 = head.next.next.value3;

Solution:

// Get head.next.next.value3

DEMO: /home/cs255001/demo/asm/4-linked-list/demo2.s

Assignment example with linked list

Translate the following assignment statement into ARM assembler:

head.value1 = head.next.next.value3;

Solution:

// Get head.next.next.value3 movw r0, #:lower16:head movt r0, #:upper16:head // r0 = addr(head) ldr r0, [r0] // r0 = head

DEMO: /home/cs255001/demo/asm/4-linked-list/demo2.s

Assignment example with linked list

Translate the following assignment statement into ARM assembler:

head.value1 = head.next.next.value3;

Solution:

// Get head.next.next.value3 movw r0, #:lower16:head movt r0, #:upper16:head // r0 = addr(head) ldr r0, [r0] // r0 = head ldr r0, [r0, #8] // r0 = head.next

DEMO: /home/cs255001/demo/asm/4-linked-list/demo2.s

Assignment example with linked list

Translate the following assignment statement into ARM assembler:

head.value1 = head.next.next.value3;

Solution:

// Get head.next.next.value3 movw r0, #:lower16:head movt r0, #:upper16:head // r0 = addr(head) ldr r0, [r0] // r0 = head ldr r0, [r0, #8] // r0 = head.next ldr r0, [r0, #8] // r0 = head.next.next

DEMO: /home/cs255001/demo/asm/4-linked-list/demo2.s

Assignment example with linked list

Translate the following assignment statement into ARM assembler:

head.value1 = head.next.next.value3;

Solution:

// Get head.next.next.value3 movw r0, #:lower16:head movt r0, #:upper16:head // r0 = addr(head) ldr r0, [r0] // r0 = head ldr r0, [r0, #8] // r0 = head.next ldr r0, [r0, #8] // r0 = head.next.next ldrsh r0, [r0, #6] // r0 = head.next.next.value3 // Store r0 in head.value1

DEMO: /home/cs255001/demo/asm/4-linked-list/demo2.s

Assignment example with linked list

Translate the following assignment statement into ARM assembler:

head.value1 = head.next.next.value3;

Solution:

// Get head.next.next.value3 movw r0, #:lower16:head movt r0, #:upper16:head // r0 = addr(head) ldr r0, [r0] // r0 = head ldr r0, [r0, #8] // r0 = head.next ldr r0, [r0, #8] // r0 = head.next.next ldrsh r0, [r0, #6] // r0 = head.next.next.value3 // Store r0 in head.value1 movw r1, #:lower16:head movt r1, #:upper16:head // r0 = addr(head) ldr r1, [r1] // r0 = head

DEMO: /home/cs255001/demo/asm/4-linked-list/demo2.s

Assignment example with linked list

Translate the following assignment statement into ARM assembler:

head.value1 = head.next.next.value3;

Solution:

// Get head.next.next.value3 movw r0, #:lower16:head movt r0, #:upper16:head // r0 = addr(head) ldr r0, [r0] // r0 = head ldr r0, [r0, #8] // r0 = head.next ldr r0, [r0, #8] // r0 = head.next.next ldrsh r0, [r0, #6] // r0 = head.next.next.value3 // Store r0 in head.value1 movw r1, #:lower16:head movt r1, #:upper16:head // r0 = addr(head) ldr r1, [r1] // r0 = head str r0, [r1, #0] // offset(value1) = 0 (int)

DEMO: /home/cs255001/demo/asm/4-linked-list/demo2.s