GDB TLS testing

[John Baldwin]

First, I tried to boot FreeBSD under QEMU (but not using an ISO image to
boot, building a disk image via makefs so I could modify it, etc.) following
these instructions:

- make buildworld TARGET_ARCH=powerpc64 CROSS_TOOLCHAIN=powerpc64-gcc
- make buildkernel TARGET_ARCH=powerpc64 CROSS_TOOLCHAIN=powerpc64-gcc KERNCONF=GENERIC64
- make installkernel TARGET_ARCH=powerpc64 CROSS_TOOLCHAIN=powerpc64-gcc KERNCONF=GENERIC64 DESTDIR=/qemu/ppc64/rootfs/
- make installworld TARGET_ARCH=powerpc64 CROSS_TOOLCHAIN=powerpc64-gcc DESTDIR=/qemu/ppc64/rootfs/
- make distribution TARGET_ARCH=powerpc64 CROSS_TOOLCHAIN=powerpc64-gcc DESTDIR=/qemu/ppc64/rootfs/
- etcupdate extract -B -D /qemu/ppc64/rootfs -s /home/john/work/freebsd/head -M "TARGET_ARCH=powerpc64 CROSS_TOOLCHAIN=powerpc64-gcc"
- makefs -M 32g -f 200000 -o version=2 -B big /qemu/ppc64/fs.img /qemu/ppc64/rootfs
- mkimg -s mbr -p prepboot:=/qemu/ppc64/rootfs/boot/boot1.elf -p freebsd:=/qemu/ppc64/fs.img -a 1 -o /qemu/ppc64/disk.img
- qemu-system-ppc64 -drive file=/qemu/ppc64/disk.img,format=raw -nographic -vga none -nic tap,ifname=tap2

This did let me boot into QEMU, but I had some weird issues with keyboard
input not always working correctly.  The network interface (llan0) also did
not work at all.  When it tried to DHCP, I saw no traffic on the tap2
interface on the host.  I also tried using '-nic user' and that wasn't able
to DHCP either.  It seems like it if_llan(4) isn't actually transmitting
packets.

Anyway, the thing I am trying to test is support for thread-local-storage
(TLS) variables under GDB.  Since networking wasn't working, I tried to
just copy my test programs (cross-built) and a GDB binary (also cross-built)
into the disk image and booting that.  However, my test program that used
threads core dumped just trying to create a 3rd thread (so second call to
pthread_create()), and when I tried to use GDB either live or against a
core, it would just spin in userland forever (probably because C++ exceptions
aren't working).  Fixing C++ probably means moving to LLVM's libunwind instead
of the ancient libgcc from gcc4.2 (though I know Mark Millard has a patch for
the ancient libgcc that helped in his testing).

Would someone with a working ppc system be willing to help test the GDB bits
for me?  You can grab the 'fbsd_tls' branch from github/bsdjhb/gdb.git to
build a GDB.  For testing purposes, just generating a core from the test
programs I'm using and looking at that core on a non-ppc host would also
work fine.  For example, in my case where I have the ppc system installed to
/qemu/ppc64/rootfs, I would do 'set sysroot /qemu/ppc64/rootfs' at the GDB
prompt to point GDB at the ppc64 libraries, etc.  Note that modern GDB is
written in C++11, so you can't build it with gcc4.2.

The first test program I am using is below and should generate a core when
run.  To test the TLS functionality you would want to make sure 'p id'
reports the proper value (PID from the program's output), and also that
'p &id' also reports an address matching the program's output:

#include <stdio.h>
#include <unistd.h>

static __thread int id;

int
main(int ac, char **av)
{

	printf("main: PID %d\n", getpid());
	id = getpid();
	printf("id = %d (%p)\n", id, &id);
	(void)getchar();
#if 1
#if defined(__powerpc__)
	*(char *)NULL = 1;
#else
	__builtin_trap();
#endif
#endif
	return (0);
}


-- 
John Baldwin