linux-kernel - Re: qemu m68k/mcf5208: problem with signal handler

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Date:	Mon, 9 May 2016 10:58:15 +0200
From:	Waldemar Brodkorb <wbx@...nadk.org>
To:	Waldemar Brodkorb <wbx@...nadk.org>
Cc:	linux-kernel@...r.kernel.org,
	Denys Vlasenko <vda.linux@...glemail.com>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Gustavo Zacarias <gustavo@...arias.com.ar>,
	Greg Ungerer <gerg@...inux.org>
Subject: Re: qemu m68k/mcf5208: problem with signal handler

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?
> 
> 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
>