Re: linux-next: build failure after merge of the modules tree

[Jessica Yu]

+++ Stephen Rothwell [10/02/21 08:50 +1100]:
> Hi Jessica,
>
> On Tue, 9 Feb 2021 16:16:20 +0100 Jessica Yu <jeyu@xxxxxxxxxx> wrote:
> > Hmm, these errors don't look like it's related to that particular commit. I was
>
> I found this commit by bisection and then tested by reverting it.
>
> Before this commit, CONFIG_TRIM_UNUSED_KSYMS would not be set in the
> allyesconfig build because CONFIG_UNUSED_SYMBOLS was set.  After this
> commit, CONFIG_TRIM_UNUSED_KSYMS will be set in the allyesconfig build.

Ah, that makes sense then. I would get the error on powerpc whenever
CONFIG_TRIM_UNUSED_KSYMS was enabled.

> > able to reproduce these weird autoksym errors even without any modules-next
> > patches applied, and on a clean v5.11-rc7 tree. To reproduce it,
> > CONFIG_TRIM_UNUSED_KSYMS needs to be enabled. I guess that's why we run into
> > these errors with allyesconfig. I used a gcc-7 ppc64le cross compiler and got
> > the same compiler warnings. It seems to not compile on powerpc properly because
> > it looks like some symbols have an extra dot "." prefix, for example in
> > kthread.o:
> >
> >     168: 0000000000000318    24 NOTYPE  GLOBAL DEFAULT    6 kthread_create_worker
> >     169: 0000000000001d90   104 FUNC    GLOBAL DEFAULT    1 .kthread_create_worker
> >     170: 0000000000000330    24 NOTYPE  GLOBAL DEFAULT    6 kthread_create_worker_on_cpu
> >     171: 0000000000001e00    88 FUNC    GLOBAL DEFAULT    1 .kthread_create_worker_on_cpu
> >     172: 0000000000000348    24 NOTYPE  GLOBAL DEFAULT    6 kthread_queue_work
> >     173: 0000000000001e60   228 FUNC    GLOBAL DEFAULT    1 .kthread_queue_work
> >
> > So I suppose this dot prefix is specific to powerpc. From the ppc64 elf abi docs:
> >
> >      Symbol names with a dot (.) prefix are reserved for holding entry point
> >      addresses. The value of a symbol named ".FN", if it exists, is the entry point
> >      of the function "FN".
> >
> > I guess the presence of the extra dot symbols is confusing
> > scripts/gen_autoksyms.sh, so we get the dot symbols in autoksyms.h, which the
> > preprocessor doesn't like. I am wondering how this was never caught until now
> > and also now curious if this feature was ever functional on powerpc..
>
> Which feature?

Sorry, by "feature" I meant CONFIG_TRIM_UNUSED_KSYMS. This config
option was introduced around v4.7. If simply enabling it produces
these compilation errors I was wondering if it ever built properly on
powerpc.

Thanks,

Jessica