An identifier used as a label becomes an assembler symbol, which represent an address in the program. Labels within a file must be unique.
NOTE
A mnemonic cannot begin in column 1 or it will be interpreted as a label. Mnemonic opcodes and assembler directive names without the . prefix are valid label names. Remember to always use whitespace before the mnemonic, or the assembler will think the identifier is a new label definition.
Symbols derived from labels can also be used as the operands of .bss, .global, .ref, or .def directives.
.global _f
LDR A1, CON1
STR A1, [sp, #0]
BL _f
CON1: .field -269488145,32