Assembler User GuidePreface Overview of the Assembler Overview of the ARM Architecture Structure of Assembly Language Modules Writing ARM Assembly Language About the Unified Assembler Language Register usage in subroutine calls Load immediate values Load immediate values using MOV and MVN Load immediate values using MOV32 Load immediate values using LDR Rd, =const Literal pools Load addresses into registers Load addresses to a register using ADR Load addresses to a register using ADRL Load addresses to a register using LDR Rd, =label Other ways to load and store registers Load and store multiple register instructions Load and store multiple register instructions in A Stack implementation using LDM and STM Stack operations for nested subroutines Block copy with LDM and STM Memory accesses The Read-Modify-Write operation Optional hash with immediate constants Use of macros Test-and-branch macro example Unsigned integer division macro example Instruction and directive relocations Frame directives Exception tables and Unwind tables Assembly language changes after RVCT v2.1 Condition Codes Using the Assembler Symbols, Literals, Expressions, and Operators VFP Programming Assembler Command-line Options ARM and Thumb Instructions VFP Instructions Directives Reference Via File Syntax
Load addresses to a register using LDR Rd, =label
4.11 Load addresses to a register using LDR Rd, =label
The assembler converts an
Example of loading using LDR Rd, =label
The following example shows a section with two literal pools. The final
The instructions listed in the comments are the ARM instructions generated by the assembler.
AREA LDRlabel, CODE, READONLY ENTRY ; Mark first instruction to execute start BL func1 ; Branch to first subroutine BL func2 ; Branch to second subroutine stop MOV r0, #0x18 ; angel_SWIreason_ReportException LDR r1, =0x20026 ; ADP_Stopped_ApplicationExit SVC #0x123456 ; ARM semihosting (formerly SWI) func1 LDR r0, =start ; => LDR r0,[PC, #offset into Literal Pool 1] LDR r1, =Darea + 12 ; => LDR r1,[PC, #offset into Literal Pool 1] LDR r2, =Darea + 6000 ; => LDR r2,[PC, #offset into Literal Pool 1] BX lr ; Return LTORG ; Literal Pool 1 func2 LDR r3, =Darea + 6000 ; => LDR r3,[PC, #offset into Literal Pool 1] ; (sharing with previous literal) ; LDR r4, =Darea + 6004 ; If uncommented, produces an error because ; Literal Pool 2 is out of range. BX lr ; Return Darea SPACE 8000 ; Starting at the current location, clears ; a 8000 byte area of memory to zero. END ; Literal Pool 2 is automatically inserted ; after the END directive. ; It is out of range of all the LDR ; pseudo-instructions in this example.
Example of string copy
The following example shows an ARM code routine that overwrites one string with another. It uses the
The example also shows how, unlike the
AREA StrCopy, CODE, READONLY ENTRY ; Mark first instruction to execute start LDR r1, =srcstr ; Pointer to first string LDR r0, =dststr ; Pointer to second string BL strcopy ; Call subroutine to do copy stop MOV r0, #0x18 ; angel_SWIreason_ReportException LDR r1, =0x20026 ; ADP_Stopped_ApplicationExit SVC #0x123456 ; ARM semihosting (formerly SWI) strcopy LDRB r2, [r1],#1 ; Load byte and update address STRB r2, [r0],#1 ; Store byte and update address CMP r2, #0 ; Check for zero terminator BNE strcopy ; Keep going if not MOV pc,lr ; Return AREA Strings, DATA, READWRITE srcstr DCB "First string - source",0 dststr DCB "Second string - destination",0 END
of your data.