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Accessing sp (r13), lr (r14), and pc (r15) in legacy code

The following methods enable you to access the sp, lr, and pc registers correctly in your source code:

Method 1

Use the compiler intrinsics in inline assembly, for example:

void printReg()
{
    unsigned int spReg, lrReg, pcReg;
    __asm
    {
        MOV spReg, __current_sp()
        MOV pcReg, __current_pc()
        MOV lrReg, __return_address()
    }
    printf("SP = 0x%X\n",spReg);
    printf("PC = 0x%X\n",pcReg);
    printf("LR = 0x%X\n",lrReg);
}
Method 2

Use embedded assembly to access physical ARM registers from within a C or C++ source file, for example:

__asm void func()
{
    MOV r0, lr
    ...
    BX lr
}

This enables the return address of a function to be captured and displayed, for example, for debugging purposes, to show the call tree.

Note

The compiler might also inline a function into its caller function. If a function is inlined, then the return address is the return address of the function that calls the inlined function. Also, a function might be tail called.