Category Archives: assembly_language

ARM assembly language

Parameter passing

  1. use registers for first 4 parameters (r0, r1, r2, r3);
  2. use stack beyond;
  3. return using r0.
  4. Functions can freely modify registers R0–R3 and R12. If a function needs to use R4 through R11, it is necessary to push their current register values onto the stack, use the register, and then pop the old value off the stack before returning.

Variable declaration

.balign 4      //  ensure the next address will start a 4-byte boundary.

myvar1: .word 3  // .word directive states that the assembler tool should emit the value of the argument of the directive as a 4 byte integer. the initial value of the variable is 3.

Instructions

ANDS {Rd,} Rn, Rm

ORRS {Rd,} Rn, Rm  ==> inclusive OR           Used to set bits

EORS {Rd,} Rn, Rm  ==> exclusive OR (only true if the corresponding bits differ)

BICS {Rd,} Rn, Rm  == >                           Used to clear bits

TEQ{cond} Rn, Operand2  == > same as EORs, except that the result is discarded ==> use for check if the bits of Rn is same as Operand2, result is 0 if same; result is 1 if different.

BEQ label                        ==> branch if equal to 0; used in conjunction with the previous instruction

MOV Rd, #expr

MOV Rd, Rm

MVN Rd, Rm  ==> takes the value in Rm, performs a bitwise logical NOT operation on the value, and places the result in Rd.

NEG Rd, Rm   ==> takes the value in Rm, multiplies it by –1, and places the result in Rd.

MOV r0, r0, LSL #1   ==> r0 << 1

 

arm_regs
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