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ARM Intrinsics Syntax

Sajid Rabbani Avagundam
  • Note: This was originally posted on 13th July 2011 at http://forums.arm.com

    Presently we are using few intrinsics as below: (thou they are in macro form!)

    #define CP15_CONTROL_READ(x)    asm("mrc p15, 0, %0, c1, c0, 0":"=r"(x))
    #define CP15_CONTROL_WRITE(x)    asm("mcr p15, 0, %0, c1, c0, 0"::"r"(x))

    we do not know how to use 'x' type of variables in case of multiple operands in intructions like add as mentioned above.

    with some exploration in generic linux source code for arm, we derived below macro translation for ADD:

    #define ADD2(sum, input1, input2) asm("ADD %2, %0, %1" :"=r"(input1),"=r"(input2) : "r"(sum) : "cc");

    however, this does not translate to an 'add' instruction when objdump is generated. help!
  • Note: This was originally posted on 14th July 2011 at http://forums.arm.com

    we have able to identify the general form of an inline assembler statement:

    asm(code : output operand list : input operand list : clobber list);with this, we derived as below for our above example:
    #define ADD(sum, input1, input2) asm("add %0, %1, %2" : "=r"(sum) : "r"(input1),"r"(input2))

    with this, three operand inline assembly is working fine :).
  • Arm Employee Badge
    Note: This was originally posted on 13th July 2011 at http://forums.arm.com

    AFAIK there are usually only intrinsics for instructions that it would be difficult or impossible for a compiler to generate from C code.  Such as the accessing control registers, or NEON ops.

    The intrinsics which do exist can be found here:

    http://infocenter.arm.com/help/topic/com.arm.doc.dui0472c/CHDFGFAB.html

    Otherwise you could look at inline or embedded assembler.  But you should really think about what you are doing if you need an ADD instruction.