Date: Thu, 29 May 2014 14:28:29 -0700 From: Neel Natu <neelnatu@gmail.com> To: Konstantin Belousov <kostikbel@gmail.com> Cc: freebsd-amd64@freebsd.org Subject: Re: i386 Go programs crash on amd64 Message-ID: <CAFgRE9FxkyqU4F%2BzA0Q3fd=kHdF-k9JcdPqPEa1ztD=HU3Q4qQ@mail.gmail.com> In-Reply-To: <20140529212720.GK3991@kib.kiev.ua> References: <537FD9A2.2010607@wemm.org> <20140523233444.GH74331@kib.kiev.ua> <20140524033944.GA96083@server.rulingia.com> <20140524074101.GI74331@kib.kiev.ua> <20140526113622.GB96083@server.rulingia.com> <20140526134457.GR74331@kib.kiev.ua> <20140528225542.GA46230@server.rulingia.com> <20140529013817.GF3991@kib.kiev.ua> <20140529104458.GA61598@server.rulingia.com> <CAFgRE9FVWYQNTsbXK73kDyeG_MNUS7spKvbDtCT4poxbQ5BCpA@mail.gmail.com> <20140529212720.GK3991@kib.kiev.ua>
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Hi Konstantin,
On Thu, May 29, 2014 at 2:27 PM, Konstantin Belousov
<kostikbel@gmail.com> wrote:
> On Thu, May 29, 2014 at 02:19:06PM -0700, Neel Natu wrote:
>> Hi,
>>
>> On Thu, May 29, 2014 at 3:44 AM, Peter Jeremy <peter@rulingia.com> wrote:
>> > On 2014-May-29 04:38:18 +0300, Konstantin Belousov <kostikbel@gmail.com> wrote:
>> >>Hm, I think I know what is going on. Try this, please.
>> >>At least, your test binary worked for me.
>> >
>> > Thank you. That seems to fix the problem even on non-trivial code.
>> >
>>
>> Occasionally, I run into a problem where sys arch(I386_SET_LDT) fails
>> with a ENOSPC. The golang runtime isn't checking the error return
>> correctly and proceeds to load the bogus selector value into %gs.
>>
>> ./write
>> pid 2571 comm write: signal 10 err e4 code 3 type 9 addr 0x8062446 rsp
>> 0xffffdae8 rip 0x8062446 <8e e8 83 c4 20 c3 00 00>
>> Bus error (core dumped)
>>
>> Here is the output of kdump:
>> $ kdump
>> capability mode sandbox enabled
>> 1934 ktrace RET ktrace 0
>> 1934 ktrace CALL execve(0x7fffffffed2f,0x7fffffffeae0,0x7fffffffeaf0)
>> 1934 ktrace NAMI "./write"
>> 1934 write RET execve 0
>> 1934 write CALL sysarch(0x1,0xffffdb38)
>> 1934 write RET sysarch -1 errno 28 No space left on device
>> 1934 write PSIG SIGBUS SIG_DFL code=BUS_OBJERR
>> 1934 write NAMI "write.core"
>>
>> In any case this is a problem because we aren't zeroing the LDT after
>> allocation. Here is a patch that fixes it:
>>
>> Index: sys/amd64/amd64/sys_machdep.c
>> ===================================================================
>> --- sys/amd64/amd64/sys_machdep.c (revision 266856)
>> +++ sys/amd64/amd64/sys_machdep.c (working copy)
>> @@ -462,7 +462,7 @@
>> new_ldt = malloc(sizeof(struct proc_ldt), M_SUBPROC, M_WAITOK);
>> new_ldt->ldt_base = (caddr_t)kmem_malloc(kernel_arena,
>> max_ldt_segment * sizeof(struct user_segment_descriptor),
>> - M_WAITOK);
>> + M_WAITOK | M_ZERO);
>> if (new_ldt->ldt_base == NULL) {
>> FREE(new_ldt, M_SUBPROC);
>> mtx_lock(&dt_lock);
>>
>> Ok to commit?
> Sure,
> this also should be merged back to at least stable/8.
Thanks, will do.
best
Neel
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