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 <[email protected]>
---
v3:
-As AngeloGioacchino Del Regno suggested,improve the comment and compress the code
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..9d2192156087 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, 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++;
+ } while (!!(insn & 0x80) && (bytes != sizeof(result)));
+
+ 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
On Fri, Apr 14, 2023 at 8:10 AM Haibo Li <[email protected]> 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 <[email protected]>
Way to go, remember to collect all the Reviewed-by tags before
you put the patch into Russell's patch tracker.
Yours,
Linus Walleij
> On Fri, Apr 14, 2023 at 8:10 AM Haibo Li <[email protected]> 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 <[email protected]>
>
> Way to go, remember to collect all the Reviewed-by tags before you put the
> patch into Russell's patch tracker.
>
> Yours,
> Linus Walleij
Thanks for reminding.I put the patch into Russell's patch tracker just now,
together with the three Reviewed-by tags from you,
Alexandre Mergnat and AngeloGioacchino Del Regno.
Thank you all.