Date: Sat, 24 May 2014 10:41:01 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Peter Jeremy <peter@rulingia.com> Cc: freebsd-amd64@freebsd.org Subject: Re: i386 Go programs crash on amd64 Message-ID: <20140524074101.GI74331@kib.kiev.ua> In-Reply-To: <20140524033944.GA96083@server.rulingia.com> References: <20140523225300.GA14433@server.rulingia.com> <537FD853.3000505@wemm.org> <537FD9A2.2010607@wemm.org> <20140523233444.GH74331@kib.kiev.ua> <20140524033944.GA96083@server.rulingia.com>
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On Sat, May 24, 2014 at 01:39:44PM +1000, Peter Jeremy wrote:
> On 2014-May-24 02:34:44 +0300, Konstantin Belousov <kostikbel@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
> "runtimežsetldt", which calls "runtimeži386_set_ldt" which uses "int 128".
>
> >We do support ldt for 32bit binaries on amd64.
>
> I thought it was supported.
>
> --
> Peter Jeremy
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