Date: Sat, 24 May 2014 13:39:44 +1000 From: Peter Jeremy <peter@rulingia.com> To: Konstantin Belousov <kostikbel@gmail.com> Cc: freebsd-amd64@freebsd.org Subject: Re: i386 Go programs crash on amd64 Message-ID: <20140524033944.GA96083@server.rulingia.com> In-Reply-To: <20140523233444.GH74331@kib.kiev.ua> References: <20140523225300.GA14433@server.rulingia.com> <537FD853.3000505@wemm.org> <537FD9A2.2010607@wemm.org> <20140523233444.GH74331@kib.kiev.ua>
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On 2014-May-24 02:34:44 +0300, Konstantin Belousov <kostikbel@gmail.com> wr=
ote:
>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_ld=
t()
>> >> 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=20
>> > that calls sysarch(I386_SET_FSBASE, ..) and friends. Normally this is=
=20
>> > handled transparently by static linking, but obviously that's an issue=
=20
>> > for Go.
>>=20
>> Actually, that's an even more interesting question. WHY are they using=
=20
>> i386_set_ldt()? Where is it coming from? As near as I can tell, libc,=
=20
>> 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=B7setldt", which calls "runtime=B7i386_set_ldt" which uses "int 12=
8".
>We do support ldt for 32bit binaries on amd64.
I thought it was supported.
--=20
Peter Jeremy
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