Re: [PATCH] Fix exception unwinding for ARM Cortex-M

Fredrik Hederstierna
2016-08-02T09:43:06Z

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-----Yao Qi <qiyaoltc@gmail.com> wrote: -----
>Fredrik,
>A general comment to this patch is that you need to split it. Each
>patch only addresses one issue or adds one support.

Ok, I send you first patch, this one fix EXC_RETURN values.

>We need to consider ARMv6-M as well,
>> + switch (pc)
>> + {
>> + /* From Table B1-8 and B1-9 the EXC_RETURN definition of
>> + the exception return behavior. */
>> +
>> + /* Return to Handler mode. Return stack Main. Frame type
>Extended. */
>
>I don't see anything useful the comment has. We can remove it.
>Instead, we need to document, on ARMv6-M and ARMv7-M without FP
>extension, the exc_return is 0xfffffff{1,9,d}. On ARMv7-M with FP
>extension, exc_return can be 0xffffff{e,f}{1,9,d}.

Ok, I documented also ARMv6-M in new patch.

>Please post the patch only for magic pc handling, then I can review
>and approve it.

Ok, done. Attached first patch.
I will submit next when it is ready.

Thanks & Kind Regards,
Fredrik

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diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 7820302..2c8573c 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,7 @@
+2016-08-02 Fredrik Hederstierna <fredrik.hederstierna@verisure.com>
+
+ * arm-tdep.c: Fix EXC_RETURN values for ARMv6-M and ARMv7-M.
+
2016-08-01 Joel Brobecker <brobecker@adacore.com>

* NEWS: Create a new section for the next release branch.
diff --git a/gdb/arm-tdep.c b/gdb/arm-tdep.c
index d2661cb..43436df 100644
--- a/gdb/arm-tdep.c
+++ b/gdb/arm-tdep.c
@@ -469,9 +469,11 @@ static CORE_ADDR
arm_addr_bits_remove (struct gdbarch *gdbarch, CORE_ADDR val)
{
/* On M-profile devices, do not strip the low bit from EXC_RETURN
- (the magic exception return address). */
+ (the magic exception return address).
+ According to B1.5.8 of both the ARMv6-M and ARMv7-M Reference Manuals
+ the EXC_RETURN value is 0xF in Bits[31:28]. */
if (gdbarch_tdep (gdbarch)->is_m
- && (val & 0xfffffff0) == 0xfffffff0)
+ && (val & 0xf0000000) == 0xf0000000)
return val;

if (arm_apcs_32)
@@ -2977,6 +2979,61 @@ arm_m_exception_prev_register (struct frame_info *this_frame,
prev_regnum);
}

+/* Determine if the program counter specified equals any of
+ these magic return values, called EXC_RETURN, defined by the
+ ARM v6-M and v7-M architectures.
+
+ From ARMv6-M Reference Manual B1.5.8
+ Table B1-5 Exception return behavior
+
+ EXC_RETURN Return To Return Stack
+ 0xFFFFFFF1 Handler mode Main
+ 0xFFFFFFF9 Thread mode Main
+ 0xFFFFFFFD Thread mode Process
+
+ From ARMv7-M Reference Manual B1.5.8
+ Table B1-8 EXC_RETURN definition of exception return behavior, no FP
+
+ EXC_RETURN Return To Return Stack
+ 0xFFFFFFF1 Handler mode Main
+ 0xFFFFFFF9 Thread mode Main
+ 0xFFFFFFFD Thread mode Process
+
+ Table B1-9 EXC_RETURN definition of exception return behavior, with FP
+
+ EXC_RETURN Return To Return Stack Frame Type
+ 0xFFFFFFE1 Handler mode Main Extended
+ 0xFFFFFFE9 Thread mode Main Extended
+ 0xFFFFFFED Thread mode Process Extended
+ 0xFFFFFFF1 Handler mode Main Basic
+ 0xFFFFFFF9 Thread mode Main Basic
+ 0xFFFFFFFD Thread mode Process Basic
+
+ For more details see "B1.5.8 Exception return behavior"
+ in both ARMv6-M and ARMv7-M Architecture Reference Manuals. */
+
+static int
+arm_m_pc_is_magic (CORE_ADDR pc)
+{
+ switch (pc)
+ {
+ /* Values from Tables in B1.5.8 the EXC_RETURN definitions of
+ the exception return behavior. */
+ case 0xffffffe1:
+ case 0xffffffe9:
+ case 0xffffffed:
+ case 0xfffffff1:
+ case 0xfffffff9:
+ case 0xfffffffd:
+ /* PC is magic. */
+ return 1;
+
+ default:
+ /* PC is not magic. */
+ return 0;
+ }
+}
+
/* Implementation of function hook 'sniffer' in
'struct frame_uwnind'. */

@@ -2990,14 +3047,8 @@ arm_m_exception_unwind_sniffer (const struct frame_unwind *self,
/* No need to check is_m; this sniffer is only registered for
M-profile architectures. */

- /* Exception frames return to one of these magic PCs. Other values
- are not defined as of v7-M. See details in "B1.5.8 Exception
- return behavior" in "ARMv7-M Architecture Reference Manual". */
- if (this_pc == 0xfffffff1 || this_pc == 0xfffffff9
- || this_pc == 0xfffffffd)
- return 1;
-
- return 0;
+ /* Check if exception frame returns to a magic PC value. */
+ return arm_m_pc_is_magic (this_pc);
}

/* Frame unwinder for M-profile exceptions. */