New: FTBFS on ppc64 big endian and gcc9 because of -mcall-aixdesc and missing __linux__
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: [email protected]
Reporter: [email protected]
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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[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 ([email protected]) changed:
What |Removed |Added
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CC| |[email protected]
--- Comment #1 from Segher Boessenkool ([email protected]) --- (In reply to Daniel Kolesa from comment #0)
Quoted 2 lines
On ppc64 big endian, the kernel builds with
-mcall-aixdescwhich 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 .
Quoted 3 lines
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?
Quoted 3 lines
but sadly it
breaks build since several things within the tree rely on__linux__being defined and#ifdefsome of their code based on said macro.
Those are bugs as well, then.
Quoted 7 lines
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 linkingvmlinux. It would seem that-mcall-aixdescchanges the way symbols are declared in a way that is not expected.Little endian is not affected because that one uses
-mabi=elfv2exclusively.
Of course, that is the only defined ABI for powerpc64le after all.
Quoted 2 lines
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.
Quoted 3 lines
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 :-)
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[Bug 204125] FTBFS on ppc64 big endian and gcc9 because of -mcall-aixdesc and missing __linux__
In reply to [email protected]https://bugzilla.kernel.org/show_bug.cgi?id=204125
--- Comment #2 from Daniel Kolesa ([email protected]) ---
ELFv2 works perfectly fine in BE userland, the musl libc *requires* ELFv2 on both endians and glibc works okay using either. ELFv2 was defined for both endians and there are distros that make use of it on BE (Adélie Linux supports only BE with musl libc and ELFv2, Void Linux has both BE and LE on musl and glibc, all using ELFv2).
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[Bug 204125] FTBFS on ppc64 big endian and gcc9 because of -mcall-aixdesc and missing __linux__
In reply to [email protected]https://bugzilla.kernel.org/show_bug.cgi?id=204125
--- Comment #3 from Daniel Kolesa ([email protected]) --- Also, reported in gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91135
Let's see what the compiler people have to say...
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[Bug 204125] FTBFS on ppc64 big endian and gcc9 because of -mcall-aixdesc and missing __linux__
In reply to [email protected]https://bugzilla.kernel.org/show_bug.cgi?id=204125
--- Comment #5 from Daniel Kolesa ([email protected]) ---
I have an entire distro built with it. A small number of things require minor patches. Some of these have been upstreamed, some of these are pending (for example, to make OpenSSL assembly work on BE/ELFv2, it requires about 5 lines of changes to pass all of the testsuite, and a PR for that is up). Glibc used to not work about a year ago I think, these days it works perfectly fine and we generally have no major issues with any software that already worked on BE in the first place.
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[Bug 204125] FTBFS on ppc64 big endian and gcc9 because of -mcall-aixdesc and missing __linux__
In reply to [email protected]https://bugzilla.kernel.org/show_bug.cgi?id=204125
--- Comment #4 from Segher Boessenkool ([email protected]) --- I meant GNU userland. I don't know any project that officially support BE ELFv2. No BE ELFv2 Linux ABI is defined, either, as far as I know.
It's great to hear that a lot of it works fine though :-)
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[Bug 204125] FTBFS on ppc64 big endian and gcc9 because of -mcall-aixdesc and missing __linux__
In reply to [email protected]https://bugzilla.kernel.org/show_bug.cgi?id=204125
--- Comment #6 from Daniel Kolesa ([email protected]) --- This appears to be the actual reason why the kernel fails to link without -mcall-aixdesc:
<smaeul> specifically it's the -mcall-aixdesc that's problematic. but removing it breaks recordmcount.pl, because nm is looking in the wrong section for symbols
<smaeul> so it fails to recognize static symbols and the kernel fails to link <smaeul> (quick hack is to update the local-symbol regex from "t" to "d" in recordmcount.pl)
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[Bug 204125] FTBFS on ppc64 big endian and gcc9 because of -mcall-aixdesc and missing __linux__
In reply to [email protected]https://bugzilla.kernel.org/show_bug.cgi?id=204125
--- Comment #7 from Daniel Kolesa ([email protected]) --- Btw, turns out an ELFv2 BE kernel requires little to no changes, these two commits produce a working kernel:
https://github.com/smaeul/linux/commit/7a9d26b7be68c21fd1be524ee4bf797d7b8c3c37
https://github.com/smaeul/linux/commit/c972894da682eff8905d9dbc7efd1bd0f1051bbf
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[Bug 204125] FTBFS on ppc64 big endian and gcc9 because of -mcall-aixdesc and missing __linux__
In reply to [email protected]https://bugzilla.kernel.org/show_bug.cgi?id=204125
--- Comment #8 from Daniel Kolesa ([email protected]) ---
Using this patch on my machines now:
https://gist.github.com/q66/625cbec5d7317829a302773f89533b51 seems to work well
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[Bug 204125] FTBFS on ppc64 big endian and gcc9 because of -mcall-aixdesc and missing __linux__
In reply to [email protected]https://bugzilla.kernel.org/show_bug.cgi?id=204125
Daniel Kolesa ([email protected]) changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |INVALID--- Comment #9 from Daniel Kolesa ([email protected]) --- well, gcc 9.2 doesn't have this problem anymore, so i guess it can be closed here...
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