I'm writing tools for debugging Cortex-M and I have discovered an artefact when reviewing the DWARF .debug_info section which the armcc outputs for some C source. (The exact compiler is ARM Compiler 5.05.)
For example when the C source contains a simple function such as:
int function(int a)
{
int x;
int y;
I have discovered that the .debug_info describes the x and y local variables as expected, and additionally a "hidden variable" called __result as follows:
<2><218>: Abbrev Number: 94 (DW_TAG_variable)
<219> DW_AT_name : __result
<222> DW_AT_type : DW_FORM_ref2 <0x188>
<225> DW_AT_location : 1 byte block: 50 (DW_OP_reg0 (r0))
<227> DW_AT_start_scope : 64
<228> DW_AT_artificial : 1
The clue of the "hidden" nature of this "variable", being the presence of the DW_AT_artificial flag.
I've have read the DWARF documentation regarding the DW_AT_artificial flag, which confirmed by suspicions. I've also deduced by experimentation that this feature relates to return value which this function, since this "variable" does not appear in the DWARF for a void typed function.
What I cannot find is any confirmation of this entity's use as intended by the designers of the armcc toolchain. Can anybody elaborate on the meaning and usage of my discovery?
