What is LDRH in arm?
The LDR pseudo-instruction is used for two main purposes: to generate literal constants when an immediate value cannot be moved into a register because it is out of range of the MOV and MVN instructions. to load a program-relative or external address into a register.
What does LDR stand for in arm?
Pseudo Instructions
| Pseudo Instruction | LDR |
|---|---|
| Function | Load a data in specified address (label) into register |
| Syntax | LDR , label |
What does STR do in arm?
STR instructions store a register value into memory. The memory address to load from or store to is at an offset from the register Rn . The offset is specified by the register Rm and can be shifted left by up to 3 bits using LSL . The value to load or store can be a byte, halfword, or word.
What does load do in assembly?
A load operation copies data from main memory into a register. A store operation copies data from a register into main memory . When a word (4 bytes) is loaded or stored the memory address must be a multiple of four.
What is the difference between LDR and LDRB in ARM?
LDRSB (Load Register Signed Byte) loads a byte from memory, sign-extends it to form a 32-bit word, and writes the result to a general-purpose register. LDRB (Load Register Byte) loads a byte from memory, zero-extends it to form a 32-bit word, and writes the result to a general-purpose register.
What is DCB in ARM?
The DCB directive allocates one or more bytes of memory, and defines the initial runtime contents of the memory.
What does CMP do in assembly?
The CMP instruction compares two operands. It is generally used in conditional execution. This instruction basically subtracts one operand from the other for comparing whether the operands are equal or not.
What is BNE ARM?
BNE (short for “Branch if Not Equal”) is the mnemonic for a machine language instruction which branches, or “jumps”, to the address specified if, and only if the zero flag is clear.
What is MOVS in ARM?
The MOV instruction copies the value of Operand2 into Rd . In certain circumstances, the assembler can substitute MVN for MOV , or MOV for MVN . Be aware of this when reading disassembly listings.
What is load store model in ARM?
ARM uses a load-store model for memory access which means that only load/store (LDR and STR) instructions can access memory. While on x86 most instructions are allowed to directly operate on data in memory, on ARM data must be moved from memory into registers before being operated on.
What is the difference between ldrsh and ldrh instruction?
The ldrsh instruction loads a half-word i.e. 16 bits (the h in ldrsh) and sign-extends (the s in ldrsh) it to the 32-bits of the register. The ldrh instruction would zero-extend the loaded 16-bits to 32-bits.
Why does the ldrh instruction zero extend 16-bit to 32-bit?
The ldrh instruction would zero-extend the loaded 16-bits to 32-bits. The reason you get the sign-extending behaviour is because the short type is a signed type.
Is Ldr A pseudo instruction?
Thus, ldr is in fact a pseudo instruction. As you can see, the constant referenced in the original ldr instruction is in fact stored at address 0x8 instead of in the instruction itself. The ldr instruction at address 0 then references this value using PC-relative addressing.
What is the RT2 value for ARM code?
Rt2 must be R ( t + 1). In ARM code you can use PC for R t in LDR word instructions and PC for R n in LDR instructions. Other uses of PC are not permitted in these ARM instructions. In Thumb code you can use PC for R t in LDR word instructions and PC for R n in LDR instructions.