i386 Go programs crash on amd64

[Konstantin Belousov]

On Sat, May 24, 2014 at 01:39:44PM +1000, Peter Jeremy wrote:
> On 2014-May-24 02:34:44 +0300, Konstantin Belousov <kostikbel at gmail.com> wrote:
> >On Fri, May 23, 2014 at 04:28:34PM -0700, Peter Wemm wrote:
> >> On 5/23/14, 4:22 PM, Peter Wemm wrote:
> >> > On 5/23/14, 3:53 PM, Peter Jeremy wrote:
> >> >> I've been playing with Go (lang/go) and found that i386 Go binaries
> >> >> segfault when run on amd64 (9.x, 10.x or HEAD).  I've narrowed it down
> >> >> to the LDT handling but am not sure whether it's on the FreeBSD or Go
> >> >> side.
> >> >>
> >> >> As far as I can see, the i386 binary is correctly calling i386_set_ldt()
> >> >> and the i386_set_ldt() emulation in the amd64 kernel matches the i386
> >> >> kernel - but the net result doesn't work.
> >> >>
> >> >> Can anyone offer any suggestions as to how to resolve this?
> >Provide the minimal test case.
> 
> The following go program, compiled on i386 and run on amd64 will die
> with a segmentation violation or bus error:
> -------
> package main
> 
> import "fmt"
> 
> func main() {
>         fmt.Println("Hello World")
> }
> -------
No, this is not consumable.

I need a self-contained minimal example written in C/asm.
If this is too hard to produce, give the the self-contained
binary, again as small as possible (small by comparing the
number of syscalls before the issue manifests itself).

As the absolute minimum I could start with the output on ctty
with machdep.uprintf_signal=1, but it is only for beginning.

> 
> >> >>
> >> > We don't emulate i386_set_ldt().
> >> >
> >> > The 32 bit version of libc on amd64 has a different implementation 
> >> > that calls sysarch(I386_SET_FSBASE, ..) and friends.  Normally this is 
> >> > handled transparently by static linking, but obviously that's an issue 
> >> > for Go.
> >> 
> >> Actually, that's an even more interesting question. WHY are they using 
> >> i386_set_ldt()?  Where is it coming from? As near as I can tell, libc, 
> >> libthr etc call I386_SET_GSBASE for tls.
> 
> As installed, the code is in /usr/local/go/src/pkg/runtime/sys_freebsd_386.s
> "runtime·setldt", which calls "runtime·i386_set_ldt" which uses "int 128".
> 
> >We do support ldt for 32bit binaries on amd64.
> 
> I thought it was supported.
> 
> -- 
> Peter Jeremy


-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 834 bytes
Desc: not available
URL: <http://lists.freebsd.org/pipermail/freebsd-amd64/attachments/20140524/9fff7822/attachment.sig>