linux-kernel - Re: [PATCH] ARM: use ARM unwinder for gcov

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Date:   Tue, 5 May 2020 16:42:20 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     Nathan Huckleberry <nhuck15@...il.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] ARM: use ARM unwinder for gcov

On Tue, May 5, 2020 at 4:19 PM Russell King - ARM Linux admin
<linux@...linux.org.uk> wrote:
>
> On Tue, May 05, 2020 at 04:11:56PM +0200, Arnd Bergmann wrote:
> > Using gcov on ARM fails when the frame pointer unwinder is used:
> >
> > arm-linux-gnueabi-ld: kernel/softirq.o:(.ARM.exidx+0x120): undefined reference to `__aeabi_unwind_cpp_pr0'
> > arm-linux-gnueabi-ld: init/main.o:(.ARM.exidx+0x98): undefined reference to `__aeabi_unwind_cpp_pr0'
> > arm-linux-gnueabi-ld: init/version.o:(.ARM.exidx+0x0): undefined reference to `__aeabi_unwind_cpp_pr0'
> > arm-linux-gnueabi-ld: init/do_mounts.o:(.ARM.exidx+0x28): undefined reference to `__aeabi_unwind_cpp_pr0'
> > arm-linux-gnueabi-ld: init/do_mounts_initrd.o:(.ARM.exidx+0x0): undefined reference to `__aeabi_unwind_cpp_pr0'
> > arm-linux-gnueabi-ld: init/initramfs.o:(.ARM.exidx+0x8): more undefined references to `__aeabi_unwind_cpp_pr0' follow
> >
> > This is likely a bug in clang that should be fixed in the compiler.
> > Forcing the use of the ARM unwinder in this configuration however
> > works around the problem.
>
> Or should the stub functions in arch/arm/kernel/unwind.c be moved out?

I had not realized this is only a stub. Moving them out should fix the
link failure, I can
send a patch after testing if we are sure that calling them is not a
bug in clang
that would lead to runtime failures.

       Arnd