Messages in this thread | | | Date | Wed, 12 Apr 2023 14:43:58 +0200 | Subject | Re: [PATCH] ARM:unwind:fix unwind abort for uleb128 case | From | Alexandre Mergnat <> |
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On 07/04/2023 05:33, Haibo Li 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@mediatek.com> > --- > arch/arm/kernel/unwind.c | 19 +++++++++++++++++-- > 1 file changed, 17 insertions(+), 2 deletions(-) > > diff --git a/arch/arm/kernel/unwind.c b/arch/arm/kernel/unwind.c > index 53be7ea6181b..e5796a5acba1 100644 > --- a/arch/arm/kernel/unwind.c > +++ b/arch/arm/kernel/unwind.c > @@ -20,7 +20,6 @@ > #warning Change compiler or disable ARM_UNWIND option. > #endif > #endif /* __CHECKER__ */ > -
Why delete this line ?
> #include <linux/kernel.h> > #include <linux/init.h> > #include <linux/export.h> > @@ -308,6 +307,22 @@ static int unwind_exec_pop_subset_r0_to_r3(struct unwind_ctrl_block *ctrl, > return URC_OK; > } > > +static unsigned long unwind_decode_uleb128(struct unwind_ctrl_block *ctrl) > +{ > + unsigned long result = 0; > + unsigned long insn; > + unsigned long bytes = 0;
Alphabetical order please.
> + > + do { > + insn = unwind_get_byte(ctrl); > + result |= (insn & 0x7f) << (bytes * 7); > + bytes++; > + if (bytes == sizeof(result)) > + break; > + } while (!!(insn & 0x80)); > + > + return result; > +}
Please add a blank line for readability.
> /* > * Execute the current unwind instruction. > */ > @@ -361,7 +376,7 @@ static int unwind_exec_insn(struct unwind_ctrl_block *ctrl) > if (ret) > goto error; > } else if (insn == 0xb2) { > - unsigned long uleb128 = unwind_get_byte(ctrl); > + unsigned long uleb128 = unwind_decode_uleb128(ctrl); > > ctrl->vrs[SP] += 0x204 + (uleb128 << 2); > } else {
Great job! I'm aligned with Linus Walleij's feedback about the need of few comments to explain the decode loop, even if your code is clear, light and robust.
-- Regards, Alexandre
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