[Bug 204125] FTBFS on ppc64 big endian and gcc9 because of -mcall-aixdesc and missing __linux__

https://bugzilla.kernel.org/show_bug.cgi?id=204125

Segher Boessenkool (segher@kernel.crashing.org) changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |segher@kernel.crashing.org

--- Comment #1 from Segher Boessenkool (segher@kernel.crashing.org) ---

(In reply to Daniel Kolesa from comment #0)

On ppc64 big endian, the kernel builds with `-mcall-aixdesc` which since gcc
9.x removes `__linux__` from the list of macros being defined.

This is a bug.  Please report at https://gcc.gnu.org/bugzilla .

This behavior
is supposed to be more correct (as it's in this case nothing but a hack, the
flag should apparently only be used when building for AIX)

What makes you think that?

OTOH, why does the kernel use that option?

but sadly it
breaks build since several things within the tree rely on `__linux__` being
defined and `#ifdef` some of their code based on said macro.

Those are bugs as well, then.

Just removing `-mcall-aixdesc` (and using just `-mabi=elfv1`) is however not
enough, as that instead causes countless undefined references to just about
every symbol when linking `vmlinux`. It would seem that `-mcall-aixdesc`
changes the way symbols are declared in a way that is not expected.

Little endian is not affected because that one uses `-mabi=elfv2`
exclusively.

Of course, that is the only defined ABI for powerpc64le after all.

Also, is there any reason not to allow an ELFv2 kernel to be built on big
endian?

Building it _on_ BE works just fine, of course.  But you mean building a BE
kernel using the ELFv2 ABI.  This is not supported; it would require writing
other versions for various low-level things.

ELFv2 is not supported in BE userland, either, btw.

There are some supposed performance benefits, and ELFv2 itself
supports either endianness. The current kbuild logic pretty much forces
ELFv1 for big endian and ELFv2 for little endian.

ELFv2 has a few little benefits; it is newer, there were lessons learnt.  It
would be surprising if it has better than trivial advantages for the BE kernel
though.  But feel free to try, of course :-)

-- 
You are receiving this mail because:
You are watching the assignee of the bug.