Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Mon, 02 Mar 2020 22:47:18 +0530
From:   "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>
Subject: Re: eh_frame confusion
To:     Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Segher Boessenkool <segher@kernel.crashing.org>,
        Michael Ellerman <mpe@ellerman.id.au>
Cc:     Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
References: <3b00b45f-74b5-13e3-9a98-c3d6b3bb7286@rasmusvillemoes.dk>
        <20200302124442.GI22482@gate.crashing.org>
In-Reply-To: <20200302124442.GI22482@gate.crashing.org>
MIME-Version: 1.0
User-Agent: astroid/v0.15-13-gb675b421
 (https://github.com/astroidmail/astroid)
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8BIT
Message-Id: <1583169014.zvau4om8mi.naveen@linux.ibm.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Segher Boessenkool wrote:
> On Mon, Mar 02, 2020 at 11:56:05AM +0100, Rasmus Villemoes wrote:
>> I'm building a ppc32 kernel, and noticed that after upgrading from gcc-7
>> to gcc-8 all object files now end up having .eh_frame section.
> 
> Since GCC 8, we enable -fasynchronous-unwind-tables by default for
> PowerPC.  See https://gcc.gnu.org/r259298 .
> 
>> For
>> vmlinux, that's not a problem, because they all get discarded in
>> arch/powerpc/kernel/vmlinux.lds.S . However, they stick around in
>> modules, which doesn't seem to be useful - given that everything worked
>> just fine with gcc-7, and I don't see anything in the module loader that
>> handles .eh_frame.
> 
> It is useful for debugging.  Not many people debug the kernel like this,
> of course.

I'm trying to understand if we need that. Other architectures seems to 
pass -fasynchronous-unwind-tables only for the vdso, but disable it for 
the kernel build. I suppose we can do the same.

If using -fno-asynchronous-unwind-tables, would crash/perf have 
problems?

- Naveen