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Subject: Re: Is this related to the general panic discussed in freebsd-current?
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From: Tim Kientzle <kientzle@freebsd.org>
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To: Andrew Turner <andrew@fubar.geek.nz>
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On May 6, 2013, at 4:47 AM, Andrew Turner wrote:

> On Sun, 5 May 2013 22:39:56 -0700
> Tim Kientzle <kientzle@freebsd.org> wrote:
>> Here's a version of stack_capture that allows a Clang-built
>> OABI kernel with WITNESS enabled to boot:
>>=20
>> /* In sys/arm/arm/stack_machdep.c */
>> static void
>> stack_capture(struct stack *st, u_int32_t *frame)
>> {
>>        vm_offset_t callpc;
>>=20
>>        stack_zero(st);
>>        while (INKERNEL(frame)) {
>>                callpc =3D frame[1];
>>                if (stack_put(st, callpc) =3D=3D -1)
>>                        break;
>>                frame =3D (u_int32_t *)(frame[0]);
>>        }
>> }
> It looks like this should work in most cases where fp and lr are next
> to each other (ip and sp are between them but doesn't need to be =
saved).

Disassembling an EABI kernel, there are 7930 'push' instructions with
fp and lr next to each other and only 220 without, so it looks like the =
EABI
kernel uses this frame convention as well.

So what do you think of the following?

#if defined(__ARM_EABI__)
static void
stack_capture(struct stack *st, u_int32_t *frame)
{
       vm_offset_t callpc;

       stack_zero(st);
       while (INKERNEL(frame)) {
               callpc =3D frame[1];
               if (stack_put(st, callpc) =3D=3D -1)
                       break;
               frame =3D (u_int32_t *)(frame[0]);
       }
}
#elif !defined(__clang__)
=85 old stack_capture code that works for OABI with gcc =85

#else
/*
 * Clang doesn't yet produce compliant stack frames for OABI.
 */
static void
stack_capture(=85)
{
	/* empty */
}
#endif