ARM Compiler toolchain v4.1 for µVision Using the Compiler

Using the Inline and Embedded Assemblers of the ARM Compiler
7.49 Legacy inline assembler that accesses sp, lr, or pc
The compilers in ARM Developer Suite (ADS) v1.2 and earlier enabled accesses to sp (r13), lr
(r14), and pc (r15) from inline assembly code. Example 7-8 shows how legacy inline assembly
code might use lr.
Example 7-8 Legacy inline assembly code using lr
void func()
{
int var;
__asm
{
mov var, lr /* get the return address of func() */
}
}
There is no guarantee that lr contains the return address of a function if your legacy code uses
it in inline assembly. For example, there are certain build options or optimizations that might
use lr for another purpose. The compiler in RVCT v2.0 and later reports an error similar to the
following if lr, sp or pc is used in this way:
If you have to access these registers from within a C or C++ source file, you can:
• use embedded assembly
• use the following intrinsics in inline assembly:
__current_pc() To access the pc register.
__current_sp()
To access the sp register.
__return_address() To access the lr register.
7.49.1 See also
Tasks
• Accessing sp (r13), lr (r14), and pc (r15) in legacy code on page 7-57.
Concepts
• Compiler support for inline assembly language on page 7-4
• Compiler support for embedded assembler on page 7-36.
Reference
• Instruction intrinsics on page 5-61.
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