Re: [Qemu-devel] [ANNOUNCE] QEMU 2.12.0-rc4 is now available

[Cornelia Huck <cohuck@redhat.com>]

On Tue, 24 Apr 2018 15:56:14 +0200
Laszlo Ersek <lersek@redhat.com> wrote:

> On 04/24/18 15:39, Eric Blake wrote:
> > On 04/24/2018 07:46 AM, Laszlo Ersek wrote:
> >   
> >> I just noticed two QAPI bugs introduced in 2.12, in the following two
> >> commits:
> >>
> >> (1) ca230ff33f89 ("qmp: add architecture specific cpu data for
> >> query-cpus-fast", 2018-02-26)
> >>
> >> This commit added @arch to @CpuInfoFast, but it failed to set the new
> >> field to CPU_INFO_ARCH_OTHER in qmp_query_cpus_fast(), when TARGET_S390X
> >> is not defined.  
> > 
> > We zero-initialize info->value, and info->value->arch == 0 happens to be
> > CPU_INFO_ARCH_X86 which is associated with the empty type CpuInfoOther,
> > which is no different than what we would have had with
> > CPU_INFO_ARCH_OTHER.  So the drawback is that on x86 architectures,
> > things look correct; while on sparc, ppc, mips, and tricore (which have
> > a specific type) and on all other platforms (which should use "other"),
> > the output wrongly reports "arch":"x86" but does not crash.  
> 
> I agree.

As an exercise for the reader: Figure out on which architectures I
tried this out... (Hint: one starts with s and ends with x, while the
other one starts with x.)

> 
> >   
> >>
> >> (2) 25fa194b7b11 ("RISC-V Build Infrastructure", 2018-03-07)
> >>
> >> This commit added the @riscv enum constant to @CpuInfoArch (used in both
> >> @CpuInfo and @CpuInfoFast -- the return types of the @query-cpus and
> >> @query-cpus-fast commands, respectively), and assigned, in both return
> >> structures, the @CpuInfoRISCV sub-structure to the new enum value.  
> > 
> > Ouch - we SHOULD have used 'CpuInfoOther' rather than 'CpuInfoRISCV' for
> > @CpuInfoFast.  We do NOT want to report the 'pc' field in the fast query.  
> 
> Right.
> 
> >>
> >> However, qmp_query_cpus_fast() does not populate the sub-structure, when
> >> TARGET_RISCV is defined; only qmp_query_cpus() does.  
> > 
> > Indeed, the output wrongly reports "arch":"x86" instead of
> > "arch":"riscv" - but at least things do not crash.
> >   
> >>
> >> The fixes don't look complicated. Do you want to hold the release while
> >> I post the fixes?
> >>
> >> I don't think these bugs are "show stoppers". On the other hand, QAPI is
> >> an external interface.  
> > 
> > It's too late for the 2.12 release.  We'll definitely fix things in
> > 2.12.1 (so cc the patches to qemu-stable),  
> 
> OK, will do.
> 
> > and should document in the
> > release notes that query-cpus-fast is known to report bogus "arch" data
> > for all architectures except x86 and s390, so applications should be
> > careful to not rely on the bogus information.  
> 
> <https://wiki.qemu.org/ChangeLog/2.12#Known_issues> refers to
> <https://wiki.qemu.org/Planning/2.12>, so I've added the above sentence
> to <https://wiki.qemu.org/Planning/2.12#Issues_that_will_not_be_fixed>.

The wiki updates look good to me.