On Fri, Dec 30, 2016 at 01:21:00PM +0100, Bas van Tiel wrote:

quoted

quoted

when using a signal handler as a way to context switch between
different usercontexts a reproducible exception occurs on my rpi3 in
64-bit mode. (https://gist.github.com/DanGe42/7148946)

Running the context_demo program as a 32-bit ARM executable on a
64-bit kernel is OK, running as a 32 || 64 bit executable on an x86
kernel is OK.

In the first exception the PC doesn?t look correct, and the *pmd is 0.
The 2nd exception happens after running the program again, the PC is 0x0.

A successful function trace was not possible -> complete kernel hangup
when enabling.

Is there another way to gather more information about what is happening?

I can reproduce Segmentation fault with your program on Marvell berlin SoCs
my kernel version is 4.1, I didn't tested 4.9, 4.10-rc1 etc..

Then I increased the STACKSIZE from 4096 to 8192 in context_demo.c,
everything works fine now. Maybe arm64 need a bit larger signalstack?

yes, increased STACKSIZE to 8192 helps on 4.9/4,10-rc1 but after a
while the exception still occurs, although the message is different.
The *pmd is not 0 in this case.

I defined STACKSIZE to the kernel's SIGSTKSZ (16384) and it seems to run
fine, though I'll leave it longer/overnight (on a Juno board). With the
4K signal stack it was crashing shortly after start.

-- 
Catalin