ARM architecture and programming Learning (6)

ADR pseudocommand instance

; Set the name and attributes of the program

Area adrlabel, code, readonly

Entry

Start

; Jump to the subprogram func for execution

BL func

; Call angel_swireason_reportexception

; Adp_stopped_applicationexit

; Arm semihosting SWI

Stop

MoV r0, #0x18; assign 0x18 to R0 and 0x18 to the macro angel_swireason_reportexception.

LDR R1, = 0x20026; 0x20026 is assigned to R1, 0x20026 immediately number corresponds to the macro adp_stopped_applicationexit, indicating the program

; Exit normally

SWI 0x123456; ends the program and gives control to the debugger

Define a data buffer for generating the offset of the address label relative to the PC

Ltorg

Func

The following pseudo-command ADR is compiled into: Sub r0, PC, # offset to start

ADR r0, start

The following pseudo-command ADR is compiled into: Add R1, PC, # offset to dataarea

ADR R1, dataarea

The following pseudo-command ADR assembly error, because the second operand cannot be represented by dataarea + 4300

; ADR R2. dataarea + 4300

The following pseudo-command adrl is compiled into two commands:

; Add R2, PC, # offset1

; Add R2, R2, # offset2

Adrl R3, dataarea + 4300

; Returned from the subroutine func

MoV PC, LR

; 8000-byte storage units are saved from the current location

And initialize it to 0

Dataarea space 8000

; End Assembly

End

Jump to an instance using a jump table

; Set the program name and attributes

Area jump, code, readonly

; Number of subprograms in the jump table

Num equ 2

; Entry point for Program Execution

Entry

Start

Set three parameters, and then call the sub-program arithfunc to perform arithmetic operations.

MoV r0, #0

MoV R1, #3

MoV R2, #2

; Call the subroutine arithfunc

BL arithfunc

Stop

; Call angel_swireason_reportexception

; Adp_stopped_applicationexit

; Arm semihosting SWI

; Exit from the application

MoV r0, #0x18

LDR R1, = 0x20026

SWI 0x123456

Subprogram arithfunc entry point

Arithfunc

; Determine whether the parameter of the selected subroutine is within the valid range

CMP r0, # num

Movhs PC, LR

; Read the base address of the jump table

ADR R3, jumptable

Jump to the corresponding subroutine Based on the R0 Value

Ldr pc, [R3, R0, LSL #2]

The jump table jumptable stores the addresses of subprograms.

Here there are two subprograms: doadd and dosub.

When R0 is 0, select doadd.

When R0 is 1, select dosub

Jumptable

DCD doadd

DCD dosub

; Subroutine doadd to execute addition operation

Doadd

Add r0, R1, R2

MoV PC, LR

; Subroutine dosub executes the subtraction operation

Dosub

Sub r0, R1, R2

MoV PC, LR

; End Assembly

End

Examples of Using Pseudo-command LDR

; Set the name and attributes of the program

Area ldrlabel, code, readonly

; Entry point for Program Execution

Entry

Start

Jump to the subprogram func1 and func2 for execution

BL func1

BL func2

; Macro angel_swireason_reportexception

; Adp_stopped_applicationexit

; Arm semihosting SWI

; Exit from the application

MoV r0, #0x18

LDR R1, = 0x20026

SWI 0x123456

Func1

The following pseudocommands are compiled into: LDR r0, [PC, # offset to litpool1]

LDR r0, = start

The following pseudocommands are compiled into: LDR R1, [PC, # offset to litpool1]

LDR R1, = darea + 12

The following pseudocommands are compiled into: LDR R2, [PC, # offset to litpool1]

LDR R2, = darea + 6000

; Program return

MoV PC, LR

; Character buffer literal Pool 1

Ltorg

Func2

The following pseudo commands are compiled into: LDR R3, [PC, # offset to litpool 1]

; A total of character Buffers

LDR R3, = fig + 6000

; If the following pseudo commands are not commented out, errors will occur during compilation.

Because the character buffer litpool 2 exceeds the range that can be reached by the pseudo command

; LDR R4, = darea + 6004

; Program return

MoV PC, LR

; The storage unit of 8000 bytes is retained from the current address.

And initialize the content to 0.

Darea space 8000

; Character buffer litpool2 should start from here

; It is out of the range that can be reached by the preceding pseudocommand.

End