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Assembler User Guide

Preface Overview of the Assembler Overview of the ARM Architecture Structure of Assembly Language Modules Writing ARM Assembly Language Condition Codes Using the Assembler Symbols, Literals, Expressions, and Operators VFP Programming Assembler Command-line Options ARM and Thumb Instructions ARM and Thumb instruction summary Instruction width specifiers Flexible second operand (Operand2) Syntax of Operand2 as a constant Syntax of Operand2 as a register with optional shi Shift operations Saturating instructions Condition code suffixes ADC ADD ADR (PC-relative) ADR (register-relative) ADRL pseudo-instruction AND ASR B BFC BFI BIC BKPT BL BLX BX BXJ CBZ and CBNZ CDP and CDP2 CLREX CLZ CMP and CMN CPS CPY pseudo-instruction DBG DMB DSB EOR ERET HVC ISB IT LDC and LDC2 LDM LDR (immediate offset) LDR (PC-relative) LDR (register offset) LDR (register-relative) LDR pseudo-instruction LDR, unprivileged LDREX LSL LSR MCR and MCR2 MCRR and MCRR2 MLA MLS MOV MOV32 pseudo-instruction MOVT MRC and MRC2 MRRC and MRRC2 MRS (PSR to general-purpose register) MRS (system coprocessor register to ARM register) MSR (ARM register to system coprocessor register) MSR (general-purpose register to PSR) MUL MVN NEG pseudo-instruction NOP ORN (Thumb only) ORR PKHBT and PKHTB PLD and PLI POP PUSH QADD QADD8 QADD16 QASX QDADD QDSUB QSAX QSUB QSUB8 QSUB16 RBIT REV REV16 REVSH RFE ROR RRX RSB RSC SADD8 SADD16 SASX SBC SBFX SDIV SEL SETEND SEV SHADD8 SHADD16 SHASX SHSAX SHSUB8 SHSUB16 SMC SMLAxy SMLAD SMLAL SMLALD SMLALxy SMLAWy SMLSD SMLSLD SMMLA SMMLS SMMUL SMUAD SMULxy SMULL SMULWy SMUSD SRS SSAT SSAT16 SSAX SSUB8 SSUB16 STC and STC2 STM STR (immediate offset) STR (register offset) STR, unprivileged STREX SUB SUBS pc, lr SVC SWP and SWPB SXTAB SXTAB16 SXTAH SXTB SXTB16 SXTH SYS TBB and TBH TEQ TST UADD8 UADD16 UASX UBFX UDIV UHADD8 UHADD16 UHASX UHSAX UHSUB8 UHSUB16 UMAAL UMLAL UMULL UND pseudo-instruction UQADD8 UQADD16 UQASX UQSAX UQSUB8 UQSUB16 USAD8 USADA8 USAT USAT16 USAX USUB8 USUB16 UXTAB UXTAB16 UXTAH UXTB UXTB16 UXTH WFE WFI YIELD VFP Instructions Directives Reference Via File Syntax

Syntax of Operand2 as a register with optional shift

10.5 Syntax of Operand2 as a register with optional shift

When you use an Operand2 register in an instruction, you can optionally also specify a shift value.

Syntax

Rm {, shift}
where:
Rm
is the register holding the data for the second operand.
shift
is an optional constant or register-controlled shift to be applied to Rm. It can be one of:
ASR #n
arithmetic shift right n bits, 1 ≤ n ≤ 32.
LSL #n
logical shift left n bits, 1 ≤ n ≤ 31.
LSR #n
logical shift right n bits, 1 ≤ n ≤ 32.
ROR #n
rotate right n bits, 1 ≤ n ≤ 31.
RRX
rotate right one bit, with extend.
type Rs
register-controlled shift is available in ARM code only, where:
type
is one of ASR, LSL, LSR, ROR.
Rs
is a register supplying the shift amount, and only the least significant byte is used.
-
if omitted, no shift occurs, equivalent to LSL #0.

Usage

If you omit the shift, or specify LSL #0, the instruction uses the value in Rm.
If you specify a shift, the shift is applied to the value in Rm, and the resulting 32-bit value is used by the instruction. However, the contents of the register Rm remain unchanged. Specifying a register with shift also updates the carry flag when used with certain instructions.
Related concepts
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