Random gdbserver question (x86)

[Michael Snyder]

Pedro Alves wrote:
> On Wednesday 31 March 2010 00:40:34, Michael Snyder wrote:
>> Question -- is gdbserver "multi-arch" to the extent that a 32-bit
>> gdbserver (built with target = i386) can debug a 64-bit app?
> 
> No, only the other way around.  It's "multi-arch" to the extent
> that a linux 64-bit gdbserver (built with target = x86-64) can
> debug a 32-bit app.  It used to only be, only 64x64 or 32x32 was
> possible; with multi-arch, 64x32 was made possible.
> 
>> I ask because linux-x86-low.c is full of ifdefs on the architecture.
>> It looks like most of the 64-bit code won't be compiled if the
>> build machine is 32-bit.
> 
> Correct.

And is that more-or-less true of gdb as well?  I.e., if host/target
is x86_64-linux, then gdb can debug both 32 and 64 bit apps, but if
host/target is i386-linux, then gdb can only debug 32 bit apps?

Actually, I phrase it as a question even though I am pretty sure it
is true.  My real question is "Why?".  It seems to me that if we just
included amd64-linux-nat.o and amd64-*-tdep.o in the build, then
32-bit gdb should be able to debug 64-bit native apps.