What, in the context of assembly language, is a pseudo?operation?

Question

a. ADR r0,table
b. LDR = r0,0x1234FEDC

Answer 1

The ADR operation generates the appropriate code to load a 32?bit value into a register. In this case, the address of the label ‘table’ will be loaded into r0. This instruction sets up a pointer.

The LDR = r0, instruction also loads a 32?bit value into a register. However, in this case, the value loaded is the constant in the instruction. The assembler synthesizes this instruction from other instructions. Typically, the assembler places the constant into a literal pool (constants stored as data in memory) and then uses a PC?relative instruction (LDR) to load the constant.

The following example shows the output of the debugger when this code is assembled. Note that the disassembly window shows the actual code in memory. You can see that the ADR has been turned into an ADD instruction by adding an offset to the PC to get the address of location label. Remember that the PC is 8 bytes ahead of its current value (in this case the current value is 0).

The LDR r1,= 0xAABBCCDD is transformed into LDR r1,[PC,#0x0008] which loads r1 with the value 8 bytes on from the current PC. At that location is the constant AABBCCDD.