2.3.1. Looking up an Existing Architecture

The first argument to the architecture initialization function is a struct gdbarch_info containing all the known information about this architecture (deduced from the BFD enumeration provided to gdbarch_register). The second argument is a list of the currently defined architectures within GDB.

The lookup is done using gdbarch_list_lookup_by_info. It is passed the list of existing architectures and the struct gdbarch_info (possibly updated) and returns the first matching architecture it finds, or NULL if none are found. If an architecture is found, the initialization function can finish, returning the found architecture as result.

2.3.1.1. struct gdbarch_info

The struct gdbarch_info has the following components:

struct gdbarch_info
{
  const struct bfd_arch_info *bfd_arch_info;
  int                         byte_order;
  bfd                        *abfd;
  struct gdbarch_tdep_info   *tdep_info;
  enum gdb_osabi              osabi;
  const struct target_desc   *target_desc;
};

bfd_arch_info holds the key details about the architecture. byte_order is an enumeration indicating the endianism. abfd is a pointer to the full BFD, tdep_info is additional custom target specific information, gdb_osabi is an enumeration identifying which (if any) of a number of operating specific ABIs are used by this architecture and target_desc is a set of name-value pairs with information about register usage in this target.

When the struct gdbarch initialization function is called, not all the fields are provided—only those which can be deduced from the BFD. The struct gdbarch_info is used as a look-up key with the list of existing architectures (the second argument to the initialization function) to see if a suitable architecture already exists. The tdep_info osabi and target_desc fields may be added before this lookup to refine the search.