linux-kernel - Re: [PATCH v3] ARM:unwind:fix unwind abort for uleb128 case

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Message-ID: <CACRpkdZf0vQL9bJtGaKfn0wBPTQTZWsg0G7UTB1dmXhfi_2KmA@mail.gmail.com>
Date:   Fri, 14 Apr 2023 09:19:32 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Haibo Li <haibo.li@...iatek.com>
Cc:     Russell King <linux@...linux.org.uk>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>, amergnat@...libre.com,
        linux-kernel@...r.kernel.org,
        Matthias Brugger <matthias.bgg@...il.com>,
        xiaoming.yu@...iatek.com,
        Russell King <rmk+kernel@...linux.org.uk>,
        Alex Sverdlin <alexander.sverdlin@...ia.com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, ardb@...nel.org,
        catalin.marinas@....com, a.anurag@...sung.com
Subject: Re: [PATCH v3] ARM:unwind:fix unwind abort for uleb128 case

On Fri, Apr 14, 2023 at 8:10 AM Haibo Li <haibo.li@...iatek.com> wrote:

> When unwind instruction is 0xb2,the subsequent instructions
> are uleb128 bytes.
> For now,it uses only the first uleb128 byte in code.
>
> For vsp increments of 0x204~0x400,use one uleb128 byte like below:
> 0xc06a00e4 <unwind_test_work>: 0x80b27fac
>   Compact model index: 0
>   0xb2 0x7f vsp = vsp + 1024
>   0xac      pop {r4, r5, r6, r7, r8, r14}
>
> For vsp increments larger than 0x400,use two uleb128 bytes like below:
> 0xc06a00e4 <unwind_test_work>: @0xc0cc9e0c
>   Compact model index: 1
>   0xb2 0x81 0x01 vsp = vsp + 1032
>   0xac      pop {r4, r5, r6, r7, r8, r14}
> The unwind works well since the decoded uleb128 byte is also 0x81.
>
> For vsp increments larger than 0x600,use two uleb128 bytes like below:
> 0xc06a00e4 <unwind_test_work>: @0xc0cc9e0c
>   Compact model index: 1
>   0xb2 0x81 0x02 vsp = vsp + 1544
>   0xac      pop {r4, r5, r6, r7, r8, r14}
> In this case,the decoded uleb128 result is 0x101(vsp=0x204+(0x101<<2)).
> While the uleb128 used in code is 0x81(vsp=0x204+(0x81<<2)).
> The unwind aborts at this frame since it gets incorrect vsp.
>
> To fix this,add uleb128 decode to cover all the above case.
>
> Signed-off-by: Haibo Li <haibo.li@...iatek.com>

Way to go, remember to collect all the Reviewed-by tags before
you put the patch into Russell's patch tracker.

Yours,
Linus Walleij