Hello, for a few years now, GCC has supported the scalar_storage_order attribute (and pragma) that allows specifying the storage order (endianness) of structures. This affects both the code GCC generates to access variables declared using the attribute, and also the debug info: GCC emits the DW_AT_endianity attribute to allow debuggers to work correctly with those variables as well.
However, in one specific scenario this doesn't work correctly right now: pointer types. Currently, GCC *will* swap the storage order for members of pointer type in a structure declared using scalar_storage_order, but it will *not* emit DW_AT_endianity for these fields -- and it really cannot, because the DWARF standard allows DW_AT_endianity only for DW_TAG_base_type type entries and not for DW_TAG_pointer_type entries. I'm not really sure where exactly the bug is, because I'm not quite sure if pointer types actually *should* be byte swapped. On the one hand, the typical use case of scalar_storage_order is to simplify accessing binary data (read from a file or the network) that was generated on a "foreign" architecture that uses a different byte order. Those use cases are unlikely to involve any pointer types, since pointer values from a foreign system are typically not usable on the current system anyway. On the other hand, even the name of the attribute specifically refers to *scalar* types, and the C standard does classsify pointer types amongst the scalar type. So maybe this was originally intended? If we do want to byte-swap pointer types, then I guess we need to still fix the debug info problem, which I guess would at a minimum require extending DWARF to allow DW_AT_endianity as an attribute to DW_TAG_pointer_type (and then probably also DW_TAG_reference_type, DW_TAG_rvalue_reference_type, DW_TAG_ptr_to_member_type and possibly others). Also, the implementation in GDB would need to be changed accordingly. Any comments or suggestions on what to do here? Thanks, Ulrich -- Dr. Ulrich Weigand GNU/Linux compilers and toolchain ulrich.weig...@de.ibm.com
