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Subject: Re: [PATCH] btrfs: Fix backref.c selftest compilation warning
To:     Tang Bin <tangbin@cmss.chinamobile.com>, clm@fb.com,
        josef@toxicpanda.com, dsterba@suse.com
Cc:     linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20200411154915.9408-1-tangbin@cmss.chinamobile.com>
 <ea85377e-4648-c174-2827-53173587777c@gmx.com>
 <4b1e57b3-ca0d-f3e0-f4c4-72cdfe943d7a@cmss.chinamobile.com>
From:   Qu Wenruo <quwenruo.btrfs@gmx.com>
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Date:   Sun, 12 Apr 2020 13:04:29 +0800
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On 2020/4/12 =E4=B8=8A=E5=8D=8811:21, Tang Bin wrote:
> Hi Qu:
>=20
> On 2020/4/12 8:52, Qu Wenruo wrote:
>>
>> On 2020/4/11 =E4=B8=8B=E5=8D=8811:49, Tang Bin wrote:
>>> Fix missing braces compilation warning in the ARM
>>> compiler environment:
>>> =C2=A0=C2=A0=C2=A0=C2=A0 fs/btrfs/backref.c: In function =E2=80=98is_=
shared_data_backref=E2=80=99:
>>> =C2=A0=C2=A0=C2=A0=C2=A0 fs/btrfs/backref.c:394:9: warning: missing b=
races around
>>> initializer [-Wmissing-braces]
>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct prelim_ref target =3D {0}=
;
>>> =C2=A0=C2=A0=C2=A0=C2=A0 fs/btrfs/backref.c:394:9: warning: (near ini=
tialization for
>>> =E2=80=98target.rbnode=E2=80=99) [-Wmissing-braces]
>> GCC version please.
>>
>> It looks like you're using an older GCC, as it's pretty common certain=

>> prebuild tool chain is still using outdated GCC.
>>
>> In my environment with GCC 9.2.0 natively (on aarch64) it's completely=

>> fine.
>> Thus personally I recommend to build your own tool chain using
>> buildroot, or run it natively, other than rely on prebuilt one.
>=20
> My environment:
>=20
> =C2=A0 PC : Ubuntu 16.04
>=20
> =C2=A0 Hardware : I.MX6ULL
>=20
> =C2=A0 Tool Chain : arm-linux-gnueabihf-gcc (Linaro GCC 4.9-2017.01) 4.=
9.4

That's pretty old.

You'd better fetch the newer version, as newer kernel may require higher
version gcc.

Or even build your own using tools like buildroot.

Thanks,
Qu

>=20
>>
>> In fact your fix could cause problem, as the original code is
>> initializing all members to 0, but now it's uninitialized.
>>
>> You need to locate the root cause other than blindly follow the warnin=
g.
>=20
> In hardware experiment, this approach is feasible.
>=20
> Thanks.
>=20
> Tang Bin
>=20
>>
>>
>=20
>=20


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