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:
#include <unistd.h> #include <signal.h> #include <sys/types.h> #include <sys/wait.h> static void sighandler(int sig) { write(1, "SIGNAL\n", 7); } int main() { int pid; write(1, "VFORK1\n", 7); pid = vfork(); if (pid == 0) { write(1, "EXIT1\n", 6); _exit(1); } wait(NULL); signal(SIGCHLD, sighandler); write(1, "VFORK2\n", 7); pid = vfork(); if (pid == 0) { write(1, "EXIT2\n", 6); _exit(1); } wait(NULL); write(1, "EXIT\n", 5); return 0; } 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