ARM Assembler diagnostic messages

The Microsoft ARM assemblers, armasm and armasm64, emit diagnostic warnings and errors when they encounter them. This article describes the most commonly encountered messages.

Syntax

filename ( line-number ) : [error|warning] A number : message

Diagnostic messages - Errors

A2193: this instruction generates unpredictable behavior

The ARM architecture can't guarantee what happens when this instruction is executed. For details about the well-defined forms of this instruction, consult the ARM Architecture Reference Manual.

    ADD r0, r8, pc         ; A2193: this instruction generates unpredictable behavior

A2196: instruction cannot be encoded in 16 bits

The specified instruction can't be encoded as a 16-bit Thumb instruction. Specify a 32-bit instruction, or rearrange code to bring the target label into the range of a 16-bit instruction.

The assembler may attempt to encode a branch in 16 bits and fail with this error, even though a 32-bit branch is encodable. You can solve this problem by using the .W specifier to explicitly mark the branch as 32-bit.

    ADD.N r0, r1, r2      ; A2196: instruction can't be encoded in 16 bits

    B.W label             ; OK
    B.N label             ; A2196: instruction can't be encoded in 16 bits
    SPACE 10000
label

A2202: Pre-UAL instruction syntax not allowed in THUMB region

Thumb code must use the Unified Assembler Language (UAL) syntax. The old syntax is no longer accepted

    ADDEQS r0, r1         ; A2202: Pre-UAL instruction syntax not allowed in THUMB region
    ADDSEQ r0, r1         ; OK

A2513: Rotation must be even

In ARM mode, there's an alternate syntax for specifying constants. Instead of writing #<const>, you can write #<byte>,#<rot>, which represents the constant value that's obtained by rotating the value <byte> right by <rot>. When you use this syntax, you must make the value of <rot> even.

    MOV r0, #4, #2       ; OK
    MOV r0, #4, #1       ; A2513: Rotation must be even

A2557: Incorrect number of bytes to write back

On the NEON structure load and store instructions (VLDn, VSTn), there's an alternate syntax for specifying writeback to the base register. Instead of putting an exclamation point (!) after the address, you can specify an immediate value that indicates the offset to be added to the base register. If you use this syntax, you must specify the exact number of bytes that were loaded or stored by the instruction.

    VLD1.8 {d0-d3}, [r0]!         ; OK
    VLD1.8 {d0-d3}, [r0], #32     ; OK
    VLD1.8 {d0-d3}, [r0], #100    ; A2557: Incorrect number of bytes to write back

Diagnostic messages - Warnings

A4228: Alignment value exceeds AREA alignment; alignment not guaranteed

The alignment that's specified in an ALIGN directive is greater than the alignment of the enclosing AREA. As a result, the assembler can't guarantee that the ALIGN directive will be honored.

To fix this warning, you can specify on the AREA directive an ALIGN attribute that's equal to or greater than the desired alignment.

AREA |.myarea1|
ALIGN 8           ; A4228: Alignment value exceeds AREA alignment; alignment not guaranteed

AREA |.myarea2|,ALIGN=3
ALIGN 8           ; OK

A4508: Use of this rotated constant is deprecated

In ARM mode, there's an alternate syntax for specifying constants. Instead of writing #<const>, you can write #<byte>,#<rot>, which represents the constant value that's obtained by rotating the value <byte> right by <rot>. In some contexts, ARM has deprecated the use of these rotated constants. In these cases, use the basic #<const> syntax instead.

    ANDS r0, r0, #1                ; OK
    ANDS r0, r0, #4, #2            ; A4508: Use of this rotated constant is deprecated

A4509: This form of conditional instruction is deprecated

This form of conditional instruction has been deprecated by ARM in the ARMv8 architecture. We recommend that you change the code to use conditional branches. To see which conditional instructions are still supported, consult the ARM Architecture Reference Manual.

This warning isn't emitted when the -oldit command-line switch is used.

    ADDEQ r0, r1, r8              ; A4509: This form of conditional instruction is deprecated

See also

ARM Assembler Command-Line Reference
ARM Assembler Directives