i386 Go programs crash on amd64

[Peter Jeremy]

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")
}
-------

>> >>
>> > 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: 964 bytes
Desc: not available
URL: <http://lists.freebsd.org/pipermail/freebsd-amd64/attachments/20140524/21afb008/attachment.sig>