Understanding of absolute addressing relative addressing ldr,adr in arm

LDR: is a location-related, absolute addressing, followed by the location of the value of the program is compiled when the position is determined.

For example, when a program is executed inside stepping stone, if the LDR pc is used, =copy_proc_beg the program is to pay the PC the absolute address of the Copy_proc_beg, that is, the address 0x30000000 at compile time, plus the offset address. , to achieve the jump.

The actual addressing space of the LDR pseudo instruction is 32 bits

Adr:adr is based on a PC or register, relative addressing, so this instruction is read based on the instructions at the time of the PC address + or-offset address, so it is location-independent, regardless of where to perform, the read address is based on the PC offset.

For example, start MOV r0, #10

ADR R4,start is compiled with sub r4,pc, #0xc because the current PC value is +8 for this instruction, so -0xc

However, the address space of ADR is only 4kb before and after, and must be in the same code segment