i386 Go programs crash on amd64

[Peter Wemm]

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?
>>
> 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.

-Peter