Comment # 15 on bug 936463 from Stanislav Brabec

Do I understand correctly, that we need a multi-stage cross build for the
standard cross platform:

1) Native compiler.
2) Cross binutils.
3) Cross compiler stage 1. It can compile and link with -nostd*.
4) Cross glibc.
5) Cross compiler final. It can compile and link against glibc (either with
-isystem or even without, depending on configuration).

As far as I understand, we are now trying to provide stage 1 compilers. It
should already be able to link, otherwise cross-glibc could not be built.


Here is my question:

Could stage 1 compiler work without libgcc.a, or it will need an intermediate
libgcc.a? If stage 1 is intended to work without libgcc.a, what about e. g.
__divmodhi4 and similar, reference to which could be generated by compiler?


Note that AVR (maybe except 32-bit AVR) is a bit special case.

It is a very small platform (8-bit), and it cannot host glibc, so there will
not be cross-avr-glibc-devel. There will be no shared libraries as output.

But there is a project called avr-libc in CrossToolchain:avr, which just needs
to be modified to work with gcc5 (and create some compatibility wrapers like
"avr-gcc").


Maybe AVR will be needed two stage build, but maybe not.AVR libgcc.a needs to
contain just a few functions that compiler generates, e. g. __divmodhi4.


My tests:

- As it is, linking code compiled (with some effort) with gcc5+avr-libc fails
on missing symbol __divmodhi4 (not sure whether it was referenced in the code
or avr-libc code).

- I successfully built AVR libgcc.a somehow yesterday just by "make all-target"
and got this problem away, but I am failing today:

In file included from /usr/include/bits/time.h:88:0,
                 from /usr/include/time.h:41,
                 from /usr/include/pthread.h:24,
                 from ./gthr-default.h:35,
                 from ../../../../libgcc/gthr.h:148,
                 from ../../../../libgcc/unwind-dw2.c:37:
/usr/include/bits/timex.h:50:3: error: width of '<anonymous>' exceeds its type
   int  :32; int  :32; int  :32; int  :32;
...
../../../../libgcc/static-object.mk:17: recipe for target 'unwind-dw2.o' failed


I am not sure, whether it is a problem that should go away with fix in the
comment 1. (avr-libc has no pthread.h, so it can never compile there).