Move the PC into another register with xtensa (lx6) cores-CodePudding

I'm trying to get the current PC value into an assembly routine written for xtensa (lx6) cores. After digging into the instruction set doc, I cannot see really how to achieve this. It looks as if the PC is not mapped into the 16 AR, and I cannot see it listed into the registers I can access through the RSR instruction, or even the RER instruction.

Any advice ?

CodePudding user response：

Here is a way to do this :

    .file   "getpc.S"
    .text
.Ltext0:
    .section    .text.get_pc,"ax",@progbits
    .align  4
    .global called_routine
    .type   called_routine, @function

// All this mess to get the PC (roughly) !

// This routine is called just to get the caller return address
// it is stored into the a0 register
called_routine:    
    entry   a1, 32
    mov     a2,a0
    retw.n


// This routine obtains something which contains 30 bits of the PC
// Please refer the xtensa instruction set manual (CALL8) for more information
// on how to rebuild the topmost 2 bits of it
    .align  4
    .global get_pc
    .global get_pc_return_address
    .type   get_pc, @function
get_pc:
    entry   a1, 32

    call8   called_routine
get_pc_return_address:
    mov.n   a2, a10
    retw.n

CodePudding user response：

The following macro is a portable (between xtensa core configurations) way to load full 32-bit runtime address of the label label into the register ar:

.macro get_runtime_addr ar, at, label
    mov \at, a0
    .begin no_transform
    _call0 1f
\label:
    .end no_transform
    .align 4
1:
    mov \ar, a0
    mov a0, \at
.endm

The no-transform block around the call and the following label ensures that no literal pool or jump trampoline is inserted between them.