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Preface Overview of the Compiler Getting Started with the Compiler Compiler Features Compiler Coding Practices Compiler Diagnostic Messages Using the Inline and Embedded Assemblers of the AR Compiler support for inline assembly language Inline assembler support in the compiler Restrictions on inline assembler support in the co Inline assembly language syntax with the __asm key Inline assembly language syntax with the asm keywo Inline assembler rules for compiler keywords __asm Restrictions on inline assembly operations in C an Inline assembler register restrictions in C and C+ Inline assembler processor mode restrictions in C Inline assembler Thumb instruction set restriction Inline assembler Vector Floating-Point (VFP) restr Inline assembler instruction restrictions in C and Miscellaneous inline assembler restrictions in C a Inline assembler and register access in C and C++ Inline assembler and the # constant expression spe Inline assembler and instruction expansion in C an Expansion of inline assembler instructions that us Expansion of inline assembler load and store instr Inline assembler effect on processor condition fla Inline assembler expression operands in C and C++ Inline assembler register list operands in C and C Inline assembler intermediate operands in C and C+ Inline assembler function calls and branches in C Inline assembler branches and labels in C and C++ Inline assembler and virtual registers Embedded assembler support in the compiler Embedded assembler syntax in C and C++ Effect of compiler ARM and Thumb states on embedde Restrictions on embedded assembly language functio Compiler generation of embedded assembly language Access to C and C++ compile-time constant expressi Differences between expressions in embedded assemb Manual overload resolution in embedded assembler __offsetof_base keyword for related base classes i Compiler-supported keywords for calling class memb __mcall_is_virtual(D, f) __mcall_is_in_vbase(D, f) __mcall_offsetof_vbase(D, f) __mcall_this_offset(D, f) __vcall_offsetof_vfunc(D, f) Calling nonstatic member functions in embedded ass Calling a nonvirtual member function Calling a virtual member function Accessing sp (r13), lr (r14), and pc (r15) Differences in compiler support for inline and emb Compiler Command-line Options Language Extensions Compiler-specific Features C and C++ Implementation Details What is Semihosting? Via File Syntax Summary Table of GNU Language Extensions Standard C Implementation Definition Standard C++ Implementation Definition C and C++ Compiler Implementation Limits

Accessing sp (r13), lr (r14), and pc (r15)

6.44 Accessing sp (r13), lr (r14), and pc (r15)

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

The first method uses 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);
}
The second method uses 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.
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