I just downloaded qemu-0.12.5, compiled as i386-linux-user, and tried to run a simple "fork" test. Qemu failed to emulate fork(), only left an "Invalid argument" message. I checked linux-user/system.c, and noticed the "~(CSIGNAL | CLONE_NPTL_FLAGS2))" flags. But, since I'm not very professional in kernel development, I have no idea about how to rectify it. I also searched the mailing list and found similar problems, but no one prompts a reasonable solution.
The following info may be helpful. ============ fork.c ============= #include <stdio.h> main() { int pid; if ((pid = fork()) > 0) /* parent */ { printf("parent\n"); wait(); printf("parent done\n"); } else if (pid == 0) /* child */ { printf("child: %d\n", getpid()); sleep(1); exit(0); } else { perror("fork"); } } # gcc for.c -o fork #./i386-linux-user/qemu-i386 ./a.out fork: Invalid argument jgj:~/qemu-0.12.5$ uname -a Linux server 2.6.30-2-686 #1 SMP Fri Dec 4 00:53:20 UTC 2009 i686 GNU/Linux jgj:~/qemu-0.12.5$ gcc -v Using built-in specs. Target: i486-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Debian 4.4.5-4' --with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.4 --enable-shared --enable-multiarch --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.4 --libdir=/usr/lib --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc --enable-targets=all --with-arch-32=i586 --with-tune=generic --enable-checking=release --build=i486-linux-gnu --host=i486-linux-gnu --target=i486-linux-gnu Thread model: posix gcc version 4.4.5 (Debian 4.4.5-4)