https://bugzilla.kernel.org/show_bug.cgi?id=204125
Bug ID: 204125
Summary: FTBFS on ppc64 big endian and gcc9 because of
-mcall-aixdesc and missing __linux__
Product: Platform Specific/Hardware
Version: 2.5
Kernel Version: any
Hardware: PPC-64
OS: Linux
Tree: Mainline
Status: NEW
Severity: high
Priority: P1
Component: PPC-64
Assignee: platform_ppc...@kernel-bugs.osdl.org
Reporter: li...@octaforge.org
Regression: No
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 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) 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.
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.
For now I worked around it in my distro by explicitly adding `-D__linux__` in
the kbuild where `-mcall-aixdesc` is inserted into flags, and it works, but
that's obviously just a workaround.
I'm not sure what the proper fix would be.
Also, is there any reason not to allow an ELFv2 kernel to be built on big
endian? 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.
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