[BUG?] qemuu only built with i386-softmmu

[BUG?] qemuu only built with i386-softmmu

[Steven Haigh]

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Hi all,

Looking specifically at 4.6.0.

It seems that the Makefile for qemuu uses the following:
        $$source/configure --enable-xen --target-list=i386-softmmu \
                $(QEMU_XEN_ENABLE_DEBUG) \
                --prefix=$(LIBEXEC) \
                --libdir=$(LIBEXEC_LIB) \
                --includedir=$(LIBEXEC_INC) \
                --source-path=$$source \
                --extra-cflags="-I$(XEN_ROOT)/tools/include \
                -I$(XEN_ROOT)/tools/libxc/include \
                -I$(XEN_ROOT)/tools/xenstore/include \
                -I$(XEN_ROOT)/tools/xenstore/compat/include \
                $(EXTRA_CFLAGS_QEMU_XEN)" \
                --extra-ldflags="-L$(XEN_ROOT)/tools/libxc \
                -L$(XEN_ROOT)/tools/xenstore \
                $(QEMU_UPSTREAM_RPATH)" \
                --bindir=$(LIBEXEC_BIN) \
                --datadir=$(SHAREDIR)/qemu-xen \
                --localstatedir=$(localstatedir) \
                --disable-kvm \
                --disable-docs \
                --disable-guest-agent \
                --python=$(PYTHON) \
                $(CONFIG_QEMUU_EXTRA_ARGS) \
                --cpu=$(IOEMU_CPU_ARCH) \
                $(IOEMU_CONFIGURE_CROSS); \
        $(MAKE) all

As such, this only builds the 32 bit version of qemuu. It seems that
starting a HVM with more than 4Gb of RAM fails:

libxl: debug: libxl_event.c:691:libxl__ev_xswatch_deregister: watch
w=0xa4d188: deregister unregistered
xc: detail: elf_parse_binary: phdr: paddr=0x100000 memsz=0x5b3a4
xc: detail: elf_parse_binary: memory: 0x100000 -> 0x15b3a4
xc: detail: VIRTUAL MEMORY ARRANGEMENT:
xc: detail:   Loader:   0000000000100000->000000000015b3a4
xc: detail:   Modules:  0000000000000000->0000000000000000
xc: detail:   TOTAL:    0000000000000000->000000017f000000
xc: detail:   ENTRY:    0000000000100600
xc: detail: PHYSICAL MEMORY ALLOCATION:
xc: detail:   4KB PAGES: 0x0000000000000200
xc: detail:   2MB PAGES: 0x00000000000005f7
xc: detail:   1GB PAGES: 0x0000000000000003
xc: detail: elf_load_binary: phdr 0 at 0x7ff67320f000 -> 0x7ff673260910
xc: error: Could not clear special pages (22 = Invalid argument):
Internal error
libxl: error: libxl_dom.c:1003:libxl__build_hvm: hvm building failed

In building my Xen 4.6.0 packages, I disable qemu-traditional and ONLY
build qemu-upstream - however as the value for i386-softmmu is not based
on variables, I'm not sure this makes a difference.

My question is, should this also build x86_64-softmmu as well as
i386-softmmu at a bare minimum?

-- 
Steven Haigh

Email: netwiz@crc.id.au
Web: https://www.crc.id.au
Phone: (03) 9001 6090 - 0412 935 897


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Re: [BUG?] qemuu only built with i386-softmmu

[Ian Campbell]

On Fri, 2016-02-05 at 08:09 +1100, Steven Haigh wrote:
> In building my Xen 4.6.0 packages, I disable qemu-traditional and ONLY
> build qemu-upstream - however as the value for i386-softmmu is not based
> on variables, I'm not sure this makes a difference.

QEMU in a Xen system only provides device model (DM) emulation and not any
CPU instruction emulation, so the nominal arch doesn't actually matter and
Xen build's i386 everywhere as a basically arbitrary choice.

It happens that the Xen DM part of QEMU is quite closely tied to the x86
scaffolding for various historical reasons, so we end up using qemu-system-
i386 even e.g. on ARM!

This comes up a lot, So I've also pasted the two paras above into a new
section in http://wiki.xenproject.org/wiki/QEMU_Upstream . If anyone thinks
the above is inaccurate then please edit the wiki (and post here too if you
like).

On thing I was sure on (so didn't write) is whether the second paragraph
could have an extra sentence:

    If you are using a distro supplied QEMU then the qemu-system-x86_64
    could also be used, but it makes no practical difference to the
    functionality of the system.

I wasn't sure if that was true (I suspect it is) and in any case I think
various bits of libxl etc will look for qemu-system-i386 in various paths
so a user would need to try reasonably hard to do so by giving an explicit
path and there is no real reason to do so maybe better not to muddy the
waters?

Ian.

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Re: [BUG?] qemuu only built with i386-softmmu

[Steven Haigh]

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On 05/02/16 20:51, Ian Campbell wrote:
> On Fri, 2016-02-05 at 08:09 +1100, Steven Haigh wrote:
>> In building my Xen 4.6.0 packages, I disable qemu-traditional and ONLY
>> build qemu-upstream - however as the value for i386-softmmu is not based
>> on variables, I'm not sure this makes a difference.
> 
> QEMU in a Xen system only provides device model (DM) emulation and not any
> CPU instruction emulation, so the nominal arch doesn't actually matter and
> Xen build's i386 everywhere as a basically arbitrary choice.
> 
> It happens that the Xen DM part of QEMU is quite closely tied to the x86
> scaffolding for various historical reasons, so we end up using qemu-system-
> i386 even e.g. on ARM!
> 
> This comes up a lot, So I've also pasted the two paras above into a new
> section in http://wiki.xenproject.org/wiki/QEMU_Upstream . If anyone thinks
> the above is inaccurate then please edit the wiki (and post here too if you
> like).

I think this is a great addition that explains the situation well.
Documenting these is always a good thing.

> 
> On thing I was sure on (so didn't write) is whether the second paragraph
> could have an extra sentence:
> 
>     If you are using a distro supplied QEMU then the qemu-system-x86_64
>     could also be used, but it makes no practical difference to the
>     functionality of the system.
> 
> I wasn't sure if that was true (I suspect it is) and in any case I think
> various bits of libxl etc will look for qemu-system-i386 in various paths
> so a user would need to try reasonably hard to do so by giving an explicit
> path and there is no real reason to do so maybe better not to muddy the
> waters?

Maybe go along the lines of:

"There is no practical difference between qemu-system-i386 and
qemu-system-x86_64 therefore both can be interchanged freely."

-- 
Steven Haigh

Email: netwiz@crc.id.au
Web: https://www.crc.id.au
Phone: (03) 9001 6090 - 0412 935 897


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Re: [BUG?] qemuu only built with i386-softmmu

[Ian Campbell]

On Fri, 2016-02-05 at 20:57 +1100, Steven Haigh wrote:
> 
> > On thing I was sure on (so didn't write) is whether the second
> > paragraph
> > could have an extra sentence:
> > 
> >     If you are using a distro supplied QEMU then the qemu-system-x86_64
> >     could also be used, but it makes no practical difference to the
> >     functionality of the system.
> > 
> > I wasn't sure if that was true (I suspect it is) and in any case I
> > think
> > various bits of libxl etc will look for qemu-system-i386 in various
> > paths
> > so a user would need to try reasonably hard to do so by giving an
> > explicit
> > path and there is no real reason to do so maybe better not to muddy the
> > waters?
> 
> Maybe go along the lines of:
> 
> "There is no practical difference between qemu-system-i386 and
> qemu-system-x86_64 therefore both can be interchanged freely."

Thanks, this is a good wording if it is indeed true (I'll wait for
confirmation of that before I write it on the wiki).

Ian.

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Re: [BUG?] qemuu only built with i386-softmmu

[Stefano Stabellini]

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On Fri, 5 Feb 2016, Ian Campbell wrote:
> On Fri, 2016-02-05 at 20:57 +1100, Steven Haigh wrote:
> >
> > > On thing I was sure on (so didn't write) is whether the second
> > > paragraph
> > > could have an extra sentence:
> > >
> > >     If you are using a distro supplied QEMU then the qemu-system-x86_64
> > >     could also be used, but it makes no practical difference to the
> > >     functionality of the system.
> > >
> > > I wasn't sure if that was true (I suspect it is) and in any case I
> > > think
> > > various bits of libxl etc will look for qemu-system-i386 in various
> > > paths
> > > so a user would need to try reasonably hard to do so by giving an
> > > explicit
> > > path and there is no real reason to do so maybe better not to muddy the
> > > waters?
> >
> > Maybe go along the lines of:
> >
> > "There is no practical difference between qemu-system-i386 and
> > qemu-system-x86_64 therefore both can be interchanged freely."
>
> Thanks, this is a good wording if it is indeed true (I'll wait for
> confirmation of that before I write it on the wiki).

Although it is technically true, within QEMU they are two different
build targets (i386-softmmu and x86_64-softmmu) and we only tests
i386-softmmu in OSSTest. It is possible that qemu-system-x86_64 might
break due to upstream changes while qemu-system-i386 could still work
and we might not notice.

I would write:

"There is no practical difference between qemu-system-i386 and
qemu-system-x86_64, they should be interchangeable. However only
qemu-system-i386 is regularly tested by OSSTest".

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Re: [BUG?] qemuu only built with i386-softmmu

[Ian Campbell]

On Tue, 2016-02-09 at 15:49 +0000, Stefano Stabellini wrote:
> On Fri, 5 Feb 2016, Ian Campbell wrote:
> > On Fri, 2016-02-05 at 20:57 +1100, Steven Haigh wrote:
> > > 
> > > > On thing I was sure on (so didn't write) is whether the second
> > > > paragraph
> > > > could have an extra sentence:
> > > > 
> > > >     If you are using a distro supplied QEMU then the qemu-system-
> > > > x86_64
> > > >     could also be used, but it makes no practical difference to the
> > > >     functionality of the system.
> > > > 
> > > > I wasn't sure if that was true (I suspect it is) and in any case I
> > > > think
> > > > various bits of libxl etc will look for qemu-system-i386 in various
> > > > paths
> > > > so a user would need to try reasonably hard to do so by giving an
> > > > explicit
> > > > path and there is no real reason to do so maybe better not to muddy
> > > > the
> > > > waters?
> > > 
> > > Maybe go along the lines of:
> > > 
> > > "There is no practical difference between qemu-system-i386 and
> > > qemu-system-x86_64 therefore both can be interchanged freely."
> > 
> > Thanks, this is a good wording if it is indeed true (I'll wait for
> > confirmation of that before I write it on the wiki).
>  
> Although it is technically true, within QEMU they are two different
> build targets (i386-softmmu and x86_64-softmmu) and we only tests
> i386-softmmu in OSSTest. It is possible that qemu-system-x86_64 might
> break due to upstream changes while qemu-system-i386 could still work
> and we might not notice. 
> 
> I would write:
> 
> "There is no practical difference between qemu-system-i386 and
> qemu-system-x86_64, they should be interchangeable. However only
> qemu-system-i386 is regularly tested by OSSTest".

Done in the wiki as above but I said "...by XenProject (via osstest)".

Ian.


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