I was looking for a way to reproduce easily PR 22979 by doing this:
(gdb) set architecture i386:x86-64
(gdb) set osabi none
However, I noticed that even though I did "set osabi none", the gdbarch
gdb created was for Linux:
(gdb) set debug arch 1
(gdb) set architecture i386:x86-64
...
(gdb) set osabi none
gdbarch_find_by_info: info.bfd_arch_info i386:x86-64
gdbarch_find_by_info: info.byte_order 1 (little)
gdbarch_find_by_info: info.osabi 4 (GNU/Linux) <--- Wrong?
gdbarch_find_by_info: info.abfd 0x0
gdbarch_find_by_info: info.tdep_info 0x0
gdbarch_find_by_info: Previous architecture 0x1e6fd30 (i386:x86-64)
selected
gdbarch_update_p: Architecture 0x1e6fd30 (i386:x86-64) unchanged
This is because the value GDB_OSABI_UNKNOWN has an unclear role,
sometimes meaning "no osabi" and sometimes "please selected
automatically". Doing "set osabi none" sets the requested osabi to
GDB_OSABI_UNKNOWN, in which case gdbarch_info_fill overrides it with a
value from the target description, or the built-in default osabi. This
means that it's impossible to force GDB not to use an osabi with "set
osabi". Since my GDB's built-in default osabi is Linux, it always
falls
back to GDB_OSABI_LINUX.
To fix it, I introduced GDB_OSABI_NONE, which really means "I don't
want
any osabi". GDB_OSABI_UNKNOWN can then be used only for "not set yet,
please auto-detect". GDB_OSABI_UNINITIALIZED now seems unnecessary
since it overlaps with GDB_OSABI_UNKNOWN, so I think it can be removed
and gdbarch_info::osabi can be initialized to GDB_OSABI_UNKNOWN.