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From:   Haibo Li <haibo.li@mediatek.com>
To:     <amergnat@baylibre.com>
CC:     <alexander.sverdlin@nokia.com>,
        <angelogioacchino.delregno@collabora.com>, <haibo.li@mediatek.com>,
        <linus.walleij@linaro.org>, <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>,
        <linux-mediatek@lists.infradead.org>, <linux@armlinux.org.uk>,
        <matthias.bgg@gmail.com>, <rmk+kernel@armlinux.org.uk>,
        <xiaoming.yu@mediatek.com>
Subject: Re: [PATCH] ARM:unwind:fix unwind abort for uleb128 case
Date:   Thu, 13 Apr 2023 15:19:25 +0800
Message-ID: <20230413071925.42858-1-haibo.li@mediatek.com>
In-Reply-To: <7d567846-a000-1bd2-6e43-7ca170366d76@baylibre.com>
References: <7d567846-a000-1bd2-6e43-7ca170366d76@baylibre.com>
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> On 07/04/2023 05:33, Haibo Li wrote:=0D
> > When unwind instruction is 0xb2,the subsequent instructions are=0D
> > uleb128 bytes.=0D
> > For now,it uses only the first uleb128 byte in code.=0D
> >=0D
> > For vsp increments of 0x204~0x400,use one uleb128 byte like below:=0D
> > 0xc06a00e4 <unwind_test_work>: 0x80b27fac=0D
> >    Compact model index: 0=0D
> >    0xb2 0x7f vsp =3D vsp + 1024=0D
> >    0xac      pop {r4, r5, r6, r7, r8, r14}=0D
> >=0D
> > For vsp increments larger than 0x400,use two uleb128 bytes like below:=
=0D
> > 0xc06a00e4 <unwind_test_work>: @0xc0cc9e0c=0D
> >    Compact model index: 1=0D
> >    0xb2 0x81 0x01 vsp =3D vsp + 1032=0D
> >    0xac      pop {r4, r5, r6, r7, r8, r14}=0D
> > The unwind works well since the decoded uleb128 byte is also 0x81.=0D
> >=0D
> > For vsp increments larger than 0x600,use two uleb128 bytes like below:=
=0D
> > 0xc06a00e4 <unwind_test_work>: @0xc0cc9e0c=0D
> >    Compact model index: 1=0D
> >    0xb2 0x81 0x02 vsp =3D vsp + 1544=0D
> >    0xac      pop {r4, r5, r6, r7, r8, r14}=0D
> > In this case,the decoded uleb128 result is 0x101(vsp=3D0x204+(0x101<<2)=
).=0D
> > While the uleb128 used in code is 0x81(vsp=3D0x204+(0x81<<2)).=0D
> > The unwind aborts at this frame since it gets incorrect vsp.=0D
> >=0D
> > To fix this,add uleb128 decode to cover all the above case.=0D
> >=0D
> > Signed-off-by: Haibo Li <haibo.li@mediatek.com>=0D
> > ---=0D
> >   arch/arm/kernel/unwind.c | 19 +++++++++++++++++--=0D
> >   1 file changed, 17 insertions(+), 2 deletions(-)=0D
> >=0D
> > diff --git a/arch/arm/kernel/unwind.c b/arch/arm/kernel/unwind.c index=
=0D
> > 53be7ea6181b..e5796a5acba1 100644=0D
> > --- a/arch/arm/kernel/unwind.c=0D
> > +++ b/arch/arm/kernel/unwind.c=0D
> > @@ -20,7 +20,6 @@=0D
> >   #warning    Change compiler or disable ARM_UNWIND option.=0D
> >   #endif=0D
> >   #endif /* __CHECKER__ */=0D
> > -=0D
> =0D
> Why delete this line ?=0D
It may be changed by mistake.I will restore it.=0D
> =0D
> >   #include <linux/kernel.h>=0D
> >   #include <linux/init.h>=0D
> >   #include <linux/export.h>=0D
> > @@ -308,6 +307,22 @@ static int=0D
> unwind_exec_pop_subset_r0_to_r3(struct unwind_ctrl_block *ctrl,=0D
> >       return URC_OK;=0D
> >   }=0D
> >=0D
> > +static unsigned long unwind_decode_uleb128(struct unwind_ctrl_block=0D
> > +*ctrl) {=0D
> > +     unsigned long result =3D 0;=0D
> > +     unsigned long insn;=0D
> > +     unsigned long bytes =3D 0;=0D
> =0D
> Alphabetical order please.=0D
get it.=0D
> =0D
> > +=0D
> > +     do {=0D
> > +             insn =3D unwind_get_byte(ctrl);=0D
> > +             result |=3D (insn & 0x7f) << (bytes * 7);=0D
> > +             bytes++;=0D
> > +             if (bytes =3D=3D sizeof(result))=0D
> > +                     break;=0D
> > +     } while (!!(insn & 0x80));=0D
> > +=0D
> > +     return result;=0D
> > +}=0D
> =0D
> Please add a blank line for readability.=0D
OK.=0D
> =0D
> >   /*=0D
> >    * Execute the current unwind instruction.=0D
> >    */=0D
> > @@ -361,7 +376,7 @@ static int unwind_exec_insn(struct=0D
> unwind_ctrl_block *ctrl)=0D
> >               if (ret)=0D
> >                       goto error;=0D
> >       } else if (insn =3D=3D 0xb2) {=0D
> > -             unsigned long uleb128 =3D unwind_get_byte(ctrl);=0D
> > +             unsigned long uleb128 =3D unwind_decode_uleb128(ctrl);=0D
> >=0D
> >               ctrl->vrs[SP] +=3D 0x204 + (uleb128 << 2);=0D
> >       } else {=0D
> =0D
> Great job! I'm aligned with Linus Walleij's feedback about the need of fe=
w=0D
> comments to explain the decode loop, even if your code is clear, light an=
d=0D
> robust.=0D
Thanks for reviewing the patch.I will add the comment in later patch.=0D
> =0D