arm64: Dump a basic information about generated trap.

[dchagin]

Summary

Follow b6d36090. Add a hackish debugging facility to provide a bit of
information about reason for generated trap. The dump of basic signal
information and registers are printed on the controlling terminal of the
process, if the machdep.uprintf_signal sysctl is enabled.

The print is the practical way to debug Linux binaries.

[trasz]

I’m not opposed to this patch, but isn’t this what core files are for?

[dchagin]

In D35133#798060, @trasz wrote:

I’m not opposed to this patch, but isn’t this what core files are for?

which debugger?

[trasz]

Linux, it’s a Linux core file :-) The easiest way is to use debootstrap port to bootstrap an Ubuntu Bionic userland, then chroot there and do “apt install gdb”. See https://wiki.freebsd.org/LinuxJails.

[dchagin]

In D35133#798103, @trasz wrote:

Linux, it’s a Linux core file :-) The easiest way is to use debootstrap port to bootstrap an Ubuntu Bionic userland, then chroot there and do “apt install gdb”. See https://wiki.freebsd.org/LinuxJails.

ah, thank you)) I am still using gentoo-stage3 tarball

[dchagin]

btw, with the knob on, I see many ILL_ILLTRP exceptions during reboot.
The same on amd64. IP points to disaster() signal handler of init(8).
Seems to me init(8) has some weird bug.