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

[Eric Blake]

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.

> 
> (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.

> 
> 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), 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.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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