Re: qemu m68k/mcf5208: problem with signal handler

[Greg Ungerer]

Hi Waldemar,

On 09/05/16 18:58, Waldemar Brodkorb wrote:
> Hi,
>
> forgot to add Greg in CC.
> And sorry for the whitespace fuckup in the example code.
>
> Waldemar Brodkorb wrote,
>
> > Dear kernel hackers,
> >
> > I have a problem with the signal handling under qemu-system-m68k
> > emulating coldfire mcf5208 evalboard. Following example code
> > provided by Busybox maintainer Denys Vlasenko
> > shows the problem when running on qemu:
>
> [ .. ]
>
> > You can generate a bootable image with latest buildroot, which shows the issue:
> > $ git clone git://git.buildroot.net/buildroot
> > $ cd buildroot; make qemu_m68k_mcf5208_defconfig; make
> > $ qemu-system-m68k -M mcf5208evb -cpu m5208 -kernel output/images/vmlinux -nographic
> >
> > Every command forked from busybox hush shell will lead into a segmentation fault.
> >
> > I added following printk to start investigating the problem:
> > diff -Nur linux-4.5.3.orig/arch/m68k/kernel/signal.c linux-4.5.3/arch/m68k/kernel/signal.c
> > --- linux-4.5.3.orig/arch/m68k/kernel/signal.c	2016-05-04 23:50:38.000000000 +0200
> > +++ linux-4.5.3/arch/m68k/kernel/signal.c	2016-05-09 04:24:53.885199544 +0200
> > @@ -595,6 +595,7 @@
> >   			       void __user *fp)
> >   {
> >   	int fsize = frame_extra_sizes(formatvec >> 12);
> > +	printk("avoid broken signal handler...\n");
> >   	if (fsize < 0) {
> >   		/*
> >   		 * user process trying to return with weird frame format
> >
> > But now the problem disappeared. :/
> >
> > What do you think? Is it a Kernel bug or a C library problem?

What version of linux kernel?
What version of gcc?

This sounds a lot like the problem I fixed in linux commit a9551799
("m68k: Use conventional function parameters for do_sigreturn").

Definitely try that first.

Regards
Greg


> > Busybox hush otherwise works fine for other noMMU targets as stm32
> > evalboard with cortex-m4. It also works in Qemu M68k emulating Q800
> > full MMU system.
> >
> > Thanks for any ideas,
> >   Waldemar
> >
> > http://lists.busybox.net/pipermail/busybox/2014-September/081659.html