9.46.2.2 Register Names

General-purpose registers are represented by predefined symbols of the form ‘rN’, where N represents a number between 0 and 63. However, the following registers have canonical names that must be used instead:

r54

sp

r55

lr

r56

sn

r57

idn0

r58

idn1

r59

udn0

r60

udn1

r61

udn2

r62

udn3

r63

zero

The assembler will emit a warning if a numeric name is used instead of the canonical name. The .no_require_canonical_reg_names assembler pseudo-op turns off this warning. .require_canonical_reg_names turns it back on.