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ADR (register-relative)

ADR generates a register-relative address in the destination register, for a label defined in a storage map.

Syntax

ADR{cond}{.W} Rd,label

where:

cond

is an optional condition code.

.W

is an optional instruction width specifier.

Rd

is the destination register to load.

label

is a symbol defined by the FIELD directive. label specifies an offset from the base register which is defined using the MAP directive.

label must be within a limited distance from the base register.

Usage

ADR generates code to easily access named fields inside a storage map.

Use the ADRL pseudo-instruction to assemble a wider range of effective addresses.

Restrictions

In Thumb code:

  • Rd cannot be PC

  • Rd can be SP only if the base register is SP.

Offset range and architectures

The assembler calculates the offset from the base register for you. The assembler generates an error if label is out of range.

Table 7 shows the possible offsets between the label and the current instruction.

Table 7. register-relative offsets
InstructionOffset rangeArchitectures[a]
ARM ADRSee Operand2 as a constantAll
32-bit Thumb ADR+/- 4095T2
16-bit Thumb ADR, base register is SP [b]0-1020 [c]T

[a] Entries in the Architectures column indicate that the instructions are available as follows:

All

All versions of the ARM architecture.

T2

The ARMv6T2 and above architectures.

T

The ARMv4T, ARMv5T*, ARMv6*, and ARMv7 architectures.

[b] Rd must be in the range R0-R7 or SP. If Rd is SP, the offset range is -508 to 508 and must be a multiple of 4

[c] Must be a multiple of 4.


ADR in 32-bit Thumb

You can use the .W width specifier to force ADR to generate a 32-bit instruction in Thumb code. ADR with .W always generates a 32-bit instruction, even if the address can be generated in a 16-bit instruction.

For forward references, ADR without .W, with base register SP, always generates a 16-bit instruction in Thumb code, even if that results in failure for an address that could be generated in a 32-bit Thumb ADD instruction.

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