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>
---
v2:
- As Linus Walleij and Alexandre Mergnat suggested,add comments for unwind_decode_uleb128
- As Alexandre Mergnat suggested,change variables declaration in Alphabetical order
---
 arch/arm/kernel/unwind.c | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/arch/arm/kernel/unwind.c b/arch/arm/kernel/unwind.c
index 53be7ea6181b..f37e55fcf81d 100644
--- a/arch/arm/kernel/unwind.c
+++ b/arch/arm/kernel/unwind.c
@@ -308,6 +308,29 @@ 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 bytes = 0;
+	unsigned long insn;
+	unsigned long result = 0;
+
+	/* unwind_get_byte() will advance ctrl one instruction at a time,
+	 * we loop until we get an instruction byte where bit 7 is not set.
+	 * Note:It decodes max 4 bytes to output 28bits data.
+	 * 28bits data(0xfffffff) covers vsp increments of 1073742336.
+	 * It is sufficent for unwinding stack.
+	 */
+	do {
+		insn = unwind_get_byte(ctrl);
+		result |= (insn & 0x7f) << (bytes * 7);
+		bytes++;
+		if (bytes == sizeof(result))
+			break;
+	} while (!!(insn & 0x80));
+
+	return result;
+}
+
 /*
  * Execute the current unwind instruction.
  */
@@ -361,7 +384,7 @@ 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 {
-- 
2.25.1

Il 13/04/23 09:34, Haibo Li ha scritto:
> 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>
> ---
> v2:
> - As Linus Walleij and Alexandre Mergnat suggested,add comments for unwind_decode_uleb128
> - As Alexandre Mergnat suggested,change variables declaration in Alphabetical order
> ---
>   arch/arm/kernel/unwind.c | 25 ++++++++++++++++++++++++-
>   1 file changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/kernel/unwind.c b/arch/arm/kernel/unwind.c
> index 53be7ea6181b..f37e55fcf81d 100644
> --- a/arch/arm/kernel/unwind.c
> +++ b/arch/arm/kernel/unwind.c
> @@ -308,6 +308,29 @@ 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 bytes = 0;
> +	unsigned long insn;
> +	unsigned long result = 0;
> +
> +	/* unwind_get_byte() will advance ctrl one instruction at a time,
> +	 * we loop until we get an instruction byte where bit 7 is not set.
> +	 * Note:It decodes max 4 bytes to output 28bits data.
> +	 * 28bits data(0xfffffff) covers vsp increments of 1073742336.
> +	 * It is sufficent for unwinding stack.
> +	 */

/*
  * unwind_get_byte() will advance `ctrl` one instruction at a time, so
  * loop until we get an instruction byte where bit 7 is not set.
  *
  * Note: This decodes a maximum of 4 bytes to output 28 bits data where
  * max is 0xfffffff: that will cover a vsp increment of 1073742336, hence
  * it is sufficient for unwinding the stack.
  */

> +	do {
> +		insn = unwind_get_byte(ctrl);
> +		result |= (insn & 0x7f) << (bytes * 7);
> +		bytes++;

also, I would do ...

	} while (!!(insn & 0x80) && bytes != sizeof(result));

...compressing the code and not creating any human readability concern.

after which, you can get my

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>

> Il 13/04/23 09:34, Haibo Li ha scritto:
> > 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>
> > ---
> > v2:
> > - As Linus Walleij and Alexandre Mergnat suggested,add comments for
> > unwind_decode_uleb128
> > - As Alexandre Mergnat suggested,change variables declaration in
> > Alphabetical order
> > ---
> >   arch/arm/kernel/unwind.c | 25 ++++++++++++++++++++++++-
> >   1 file changed, 24 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm/kernel/unwind.c b/arch/arm/kernel/unwind.c index
> > 53be7ea6181b..f37e55fcf81d 100644
> > --- a/arch/arm/kernel/unwind.c
> > +++ b/arch/arm/kernel/unwind.c
> > @@ -308,6 +308,29 @@ 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 bytes = 0;
> > +     unsigned long insn;
> > +     unsigned long result = 0;
> > +
> > +     /* unwind_get_byte() will advance ctrl one instruction at a time,
> > +      * we loop until we get an instruction byte where bit 7 is not set.
> > +      * Note:It decodes max 4 bytes to output 28bits data.
> > +      * 28bits data(0xfffffff) covers vsp increments of 1073742336.
> > +      * It is sufficent for unwinding stack.
> > +      */
> 
> /*
>   * unwind_get_byte() will advance `ctrl` one instruction at a time, so
>   * loop until we get an instruction byte where bit 7 is not set.
>   *
>   * Note: This decodes a maximum of 4 bytes to output 28 bits data where
>   * max is 0xfffffff: that will cover a vsp increment of 1073742336, hence
>   * it is sufficient for unwinding the stack.
>   */
Looks much better.Thanks.
> 
> > +     do {
> > +             insn = unwind_get_byte(ctrl);
> > +             result |= (insn & 0x7f) << (bytes * 7);
> > +             bytes++;
> 
> also, I would do ...
> 
>         } while (!!(insn & 0x80) && bytes != sizeof(result));
> 
> ...compressing the code and not creating any human readability concern.
> 
> after which, you can get my
> 
> Reviewed-by: AngeloGioacchino Del Regno
> <angelogioacchino.delregno@collabora.com>
get it.I will make a new patch.

On Thu, Apr 13, 2023 at 9:34 AM Haibo Li <haibo.li@mediatek.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@mediatek.com>

Thanks Haibo,
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

Please put this into Russell's patch tracker once you feel it is finished!
https://www.arm.linux.org.uk/developer/patches/

Yours,
Linus Walleij

On 13/04/2023 09:39, Linus Walleij wrote:
> On Thu, Apr 13, 2023 at 9:34 AM Haibo Li<haibo.li@mediatek.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@mediatek.com>
> Thanks Haibo,
> Reviewed-by: Linus Walleij<linus.walleij@linaro.org>

Reviewed-by: Alexandre Mergnat <amergnat@baylibre.com>


Regards,
Alexandre