ARM Compiler toolchain v4.1 for µVision Using the Compiler

Using the Inline and Embedded Assemblers of the ARM Compiler
7.39 __offsetof_base keyword for related base classes in embedded assembler
The __offsetof_base keyword enables you to determine the offset from the beginning of an
object to a base class sub-object within it:
__offsetof_base(D, B)
B must be an unambiguous, nonvirtual base class of D.
Returns the offset from the beginning of a D object to the start of the B base
subobject within it. The result might be zero. Example 7-5 shows the offset (in
bytes) that must be added to a D* p to implement the equivalent of
static_cast(p).
Example 7-5 static_cast(p)
__asm B* my_static_base_cast(D* /*p*/) // equivalent to:
// return static_cast(p)
{
if __offsetof_base(D, B) 0 // optimize zero offset case
ADD r0, r0, #__offsetof_base(D, B)
endif
BX lr
}
The __offsetof_base, __mcall_*, and _vcall_offsetof_vfunc keywords are converted into
integer or logical constants in the assembler source. You can only use it in __asm functions, not
in __cpp expressions.
7.39.1 See also
Concepts
• Restrictions on embedded assembly language functions in C and C++ code on page 7-40
• Compiler support for embedded assembler on page 7-36.
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