ARM cross-compiler with newlib, LTO, undefined reference to libc symbols

[Gabriel Marcano]

This is a continuation of trying to build some software for the Nintendo 3DS,  
which is an ARM platform. After applying the patches in  
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100767, I no longer get an ICE,
but now I'm getting a lot of undefined references to libc symbols, like free
and snprintf and malloc. Thing is, if I build this application without LTO, it
builds fine, so there appears to be something strange going on in the LTO
process that makes it so ld can't figure out how to link libc with everything
else.

Some things I've tried and done:

- I've confirmed that the libc being linked has those symbols by checking the  
  output of nm against that libc.a.

- I spent a few hours trying to step through ld to figure out how it
  determines when a symbol is undefined, but I didn't make much headway. I did
  find a place (_bfd_generic_link_add_one_symbol) where it appears to be
  setting some data structures to undefined, but I can't figure out how it's  
  making that decision (it's some sort of table???).

- I replaced the libc.a (and honestly all of lib/ for the cross-compiler, I
  made a backup to restore it after the test) with the one from devKitARM
  (from the devKitPro group, they provide GCC toolchains for a bunch of  
  Nintendo platforms), and I was still getting undefined references, so it
  doesn't seem to be a problem of how I'm building my own newlib library (or both
  of these libraries are built wrong).

- I tried to reproduce the problem with a simpler example, but I wasn't able
  to (I probably just don't know what I'm doing).

I'm more than willing to help collect information to track down the source of
the problem, but I'm going to need some pointers in the right direction. The
application in question has a somewhat convoluted build process (what is it
with embedded development communities and super fancy Makefiles?) and it also
requires specific patches against newlib (adds a new system library), so it's a
little hard for me to have someone else try to build this and reproduce it (the
"official" 3DS GCC toolchain suffers from the LTO ICE bug, so I can't check if
their libc behaves properly, and their toolchain is even more annoying to
build).

In summary, any tips on what I should be looking for to track down the cause?
 Let me know if you need more information from me also.

Thanks,

Gabe Marcano