[PING]Fix for prologue processing on PowerPC
Nikola Prica
nikola.prica@rt-rk.com
Thu Oct 26 10:02:00 GMT 2017
Can someone please take a look into this?
Thanks,
Nikola Prica
On 22.09.2017. 14:11, Nikola Prica wrote:
> After analyzing dump of ppc program, whose crash occurred after
> watchdog_force_here () function, GDB couldn't print full back trace
> because GDB couldn't unwind PC from the watchdog fucntion.
>
> The problem is introduced with the following patch:
>
> https://sourceware.org/ml/gdb-patches/2008-08/msg00245.html
>
> In function skip_prologue(), shifted lr_reg makes below condition always
> false because non-shifted lr_reg value is expected to be checked.
>
> else if (lr_reg >= 0 &&
> /* std Rx, NUM(r1) || stdu Rx, NUM(r1) */
> (((op & 0xffff0000) == (lr_reg | 0xf8010000)) ||
> /* stw Rx, NUM(r1) */
> ((op & 0xffff0000) == (lr_reg | 0x90010000)) ||
> /* stwu Rx, NUM(r1) */
> ((op & 0xffff0000) == (lr_reg | 0x94010000))))
>
> Before this fix unwinding was able to work because it relied on unwind
> directives or on some of the next frames to find PC. Problem came with
> watchdog_force_here() function which didn't contain unwind directives.
>
> I wasn't able to produce test case that would show improvements for end
> user. I suppose that changes would be visible if watchdog event was
> called, but I don't have valid ppc board to try this. I have tried this
> code on simple test case with few functions in back trace. The back
> trace is printed correctly with and without this fix, but the difference
> between those two runs is that the body of the upper condition was
> visited with this patch. After visiting the body there was no need to
> look for PC counter in next frames nor to use unwind directives.
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