Re: [PATCH] mos6522: fix linking error when CONFIG_MOS6522 is not set

[Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>]

On 04/05/2022 14:16, Murilo Opsfelder Araújo wrote:
> Hi, Mark.
> 
> On 5/4/22 04:10, Mark Cave-Ayland wrote:
>> On 02/05/2022 14:36, Murilo Opsfelder Araújo wrote:
>>
>>> Hi, Mark.
>>>
>>> Thanks for reviewing.  Comments below.
>>>
>>> On 5/2/22 06:43, Mark Cave-Ayland wrote:
>>>> On 30/04/2022 00:31, Murilo Opsfelder Araujo wrote:
>>>>
>>>>> When CONFIG_MOS6522 is not set, building ppc64-softmmu target fails:
>>>>>
>>>>>      /usr/bin/ld: libqemu-ppc64-softmmu.fa.p/monitor_misc.c.o:(.data+0x1158): 
>>>>> undefined reference to `hmp_info_via'
>>>>>      clang-13: error: linker command failed with exit code 1 (use -v to see 
>>>>> invocation)
>>>>>
>>>>> Add CONFIG_MOS6522 check for hmp_info_via in hmp-commands-info.hx to fix
>>>>> such linking error.
>>>>>
>>>>> Fixes: 409e9f7131e5 (mos6522: add "info via" HMP command for debugging)
>>>>> Signed-off-by: Murilo Opsfelder Araujo <muriloo@linux.ibm.com>
>>>>> Cc: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
>>>>> Cc: Fabiano Rosas <farosas@linux.ibm.com>
>>>>> ---
>>>>>   hmp-commands-info.hx | 2 ++
>>>>>   1 file changed, 2 insertions(+)
>>>>>
>>>>> diff --git a/hmp-commands-info.hx b/hmp-commands-info.hx
>>>>> index adfa085a9b..9ad784dd9f 100644
>>>>> --- a/hmp-commands-info.hx
>>>>> +++ b/hmp-commands-info.hx
>>>>> @@ -881,6 +881,7 @@ SRST
>>>>>   ERST
>>>>>   #if defined(TARGET_M68K) || defined(TARGET_PPC)
>>>>> +#if defined(CONFIG_MOS6522)
>>>>>       {
>>>>>           .name         = "via",
>>>>>           .args_type    = "",
>>>>> @@ -889,6 +890,7 @@ ERST
>>>>>           .cmd          = hmp_info_via,
>>>>>       },
>>>>>   #endif
>>>>> +#endif
>>>>>   SRST
>>>>>     ``info via``
>>>>
>>>> Hmmm. The patch in its proposed form isn't correct, since device CONFIG_* defines 
>>>> aren't declared when processing hmp-commands-info.hx. This was something that was 
>>>> discovered and discussed in the original thread for which the current workaround 
>>>> is to use the per-target TARGET_* defines instead.
>>>
>>> So my proposed fix worked just by coincidence.  Thanks for providing the background.
>>>
>>>>
>>>> Given that the g3beige and mac99 machines are included by default in 
>>>> qemu-system-ppc64 which both contain the MOS6522 device, I can't quite understand 
>>>> how CONFIG_MOS6522 isn't being selected.
>>>>
>>>> Can you give more information about how you are building QEMU including your 
>>>> configure command line?
>>>
>>> Here is a reproducer adapted from CentOS 9 Stream qemu-kvm[0] package
>>> (build failed on c9s ppc64le with QEMU at commit 
>>> f5643914a9e8f79c606a76e6a9d7ea82a3fc3e65):
>>>
>>> $ cat > configs/devices/rh-virtio.mak <<"EOF"
>>> CONFIG_VIRTIO=y
>>> CONFIG_VIRTIO_BALLOON=y
>>> CONFIG_VIRTIO_BLK=y
>>> CONFIG_VIRTIO_GPU=y
>>> CONFIG_VIRTIO_INPUT=y
>>> CONFIG_VIRTIO_INPUT_HOST=y
>>> CONFIG_VIRTIO_NET=y
>>> CONFIG_VIRTIO_RNG=y
>>> CONFIG_VIRTIO_SCSI=y
>>> CONFIG_VIRTIO_SERIAL=y
>>> EOF
>>>
>>> $ cat > configs/devices/ppc64-softmmu/ppc64-rh-devices.mak <<"EOF"
>>> include ../rh-virtio.mak
>>> CONFIG_DIMM=y
>>> CONFIG_MEM_DEVICE=y
>>> CONFIG_NVDIMM=y
>>> CONFIG_PCI=y
>>> CONFIG_PCI_DEVICES=y
>>> CONFIG_PCI_TESTDEV=y
>>> CONFIG_PCI_EXPRESS=y
>>> CONFIG_PSERIES=y
>>> CONFIG_SCSI=y
>>> CONFIG_SPAPR_VSCSI=y
>>> CONFIG_TEST_DEVICES=y
>>> CONFIG_USB=y
>>> CONFIG_USB_OHCI=y
>>> CONFIG_USB_OHCI_PCI=y
>>> CONFIG_USB_SMARTCARD=y
>>> CONFIG_USB_STORAGE_CORE=y
>>> CONFIG_USB_STORAGE_CLASSIC=y
>>> CONFIG_USB_XHCI=y
>>> CONFIG_USB_XHCI_NEC=y
>>> CONFIG_USB_XHCI_PCI=y
>>> CONFIG_VFIO=y
>>> CONFIG_VFIO_PCI=y
>>> CONFIG_VGA=y
>>> CONFIG_VGA_PCI=y
>>> CONFIG_VHOST_USER=y
>>> CONFIG_VIRTIO_PCI=y
>>> CONFIG_VIRTIO_VGA=y
>>> CONFIG_WDT_IB6300ESB=y
>>> CONFIG_XICS=y
>>> CONFIG_XIVE=y
>>> CONFIG_TPM=y
>>> CONFIG_TPM_SPAPR=y
>>> CONFIG_TPM_EMULATOR=y
>>> EOF
>>>
>>> $ mkdir build
>>> $ cd build
>>>
>>> $ ../configure --cc=clang --cxx=/bin/false --prefix=/usr --libdir=/usr/lib64 
>>> --datadir=/usr/share --sysconfdir=/etc --interp-prefix=/usr/qemu-%M 
>>> --localstatedir=/var --docdir=/usr/share/doc --libexecdir=/usr/libexec 
>>> '--extra-ldflags=-Wl,-z,relro -Wl,--as-needed  -Wl,-z,now   ' '--extra-cflags=-O2 
>>> -fexceptions -g -grecord-gcc-switches -pipe -Wall -Werror=format-security 
>>> -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS --config 
>>> /usr/lib/rpm/redhat/redhat-hardened-clang.cfg -fstack-protector-strong   -m64 
>>> -mcpu=power9 -mtune=power9 -fasynchronous-unwind-tables -fstack-clash-protection 
>>> -Wno-string-plus-int' --with-pkgversion=qemu-kvm-7.0.0-1.el9 
>>> --with-suffix=qemu-kvm 
>>> --firmwarepath=/usr/share/qemu-firmware:/usr/share/ipxe/qemu:/usr/share/seavgabios:/usr/share/seabios 
>>> --meson=internal --enable-trace-backend=dtrace --with-coroutine=ucontext 
>>> --with-git=git --tls-priority=@QEMU,SYSTEM --audio-drv-list= --disable-alsa 
>>> --disable-attr --disable-auth-pam --disable-avx2 --disable-avx512f 
>>> --disable-block-drv-whitelist-in-tools --disable-bochs --disable-bpf 
>>> --disable-brlapi --disable-bsd-user --disable-bzip2 --disable-cap-ng 
>>> --disable-capstone --disable-cfi --disable-cfi-debug --disable-cloop 
>>> --disable-cocoa --disable-coreaudio --disable-coroutine-pool 
>>> --disable-crypto-afalg --disable-curl --disable-curses --disable-dbus-display 
>>> --disable-debug-info --disable-debug-mutex --disable-debug-tcg --disable-dmg 
>>> --disable-docs --disable-dsound --disable-fdt --disable-fuse --disable-fuse-lseek 
>>> --disable-gcrypt --disable-gettext --disable-gio --disable-glusterfs 
>>> --disable-gnutls --disable-gtk --disable-guest-agent --disable-guest-agent-msi 
>>> --disable-hax --disable-hvf --disable-iconv --disable-jack --disable-kvm 
>>> --disable-l2tpv3 --disable-libdaxctl --disable-libiscsi --disable-libnfs 
>>> --disable-libpmem --disable-libssh --disable-libudev --disable-libusb 
>>> --disable-linux-aio --disable-linux-io-uring --disable-linux-user 
>>> --disable-live-block-migration --disable-lto --disable-lzfse --disable-lzo 
>>> --disable-malloc-trim --disable-membarrier --disable-modules 
>>> --disable-module-upgrades --disable-mpath --disable-multiprocess --disable-netmap 
>>> --disable-nettle --disable-numa --disable-nvmm --disable-opengl --disable-oss 
>>> --disable-pa --disable-parallels --disable-pie --disable-pvrdma --disable-qcow1 
>>> --disable-qed --disable-qga-vss --disable-qom-cast-debug --disable-rbd 
>>> --disable-rdma --disable-replication --disable-rng-none --disable-safe-stack 
>>> --disable-sanitizers --disable-sdl --disable-sdl-image --disable-seccomp 
>>> --disable-selinux --disable-slirp --disable-slirp-smbd --disable-smartcard 
>>> --disable-snappy --disable-sparse --disable-spice --disable-spice-protocol 
>>> --disable-strip --disable-system --disable-tcg --disable-tools --disable-tpm 
>>> --disable-u2f --disable-usb-redir --disable-user --disable-vde --disable-vdi 
>>> --disable-vhost-crypto --disable-vhost-kernel --disable-vhost-net 
>>> --disable-vhost-scsi --disable-vhost-user --disable-vhost-user-blk-server 
>>> --disable-vhost-vdpa --disable-vhost-vsock --disable-virglrenderer 
>>> --disable-virtfs --disable-virtiofsd --disable-vnc --disable-vnc-jpeg 
>>> --disable-vnc-sasl --disable-vte --disable-vvfat --disable-werror --disable-whpx 
>>> --disable-xen --disable-xen-pci-passthrough --disable-xkbcommon --disable-zstd 
>>> --with-git-submodules=ignore --without-default-devices 
>>> --with-devices-ppc64=ppc64-rh-devices --target-list=ppc64-softmmu 
>>> --block-drv-rw-whitelist=qcow2,raw,file,host_device,nbd,iscsi,rbd,blkdebug,luks,null-co,nvme,copy-on-read,throttle,compress 
>>> --block-drv-ro-whitelist=vdi,vmdk,vhdx,vpc,https --enable-attr --enable-cap-ng 
>>> --enable-capstone=internal --enable-coroutine-pool --enable-curl 
>>> --enable-debug-info --enable-docs --enable-fdt=system --enable-gnutls 
>>> --enable-guest-agent --enable-iconv --enable-kvm --enable-libusb --enable-libudev 
>>> --enable-linux-aio --enable-lzo --enable-malloc-trim --enable-modules 
>>> --enable-mpath --enable-numa --enable-pa --enable-pie --enable-rbd --enable-rdma 
>>> --enable-seccomp --enable-selinux --enable-slirp=system --enable-snappy 
>>> --enable-spice-protocol --enable-system --enable-tcg --enable-tools --enable-tpm 
>>> --enable-vdi --enable-virtiofsd --enable-vhost-kernel --enable-vhost-net 
>>> --enable-vhost-user --enable-vhost-user-blk-server --enable-vhost-vdpa 
>>> --enable-vhost-vsock --enable-vnc --enable-vnc-sasl --enable-werror 
>>> --enable-xkbcommon
>>>
>>> $ make -O -j$(nproc) V=1 VERBOSE=1
>>> ...
>>> /usr/bin/ld: libqemu-ppc64-softmmu.fa.p/monitor_misc.c.o:(.data+0x1158): undefined 
>>> reference to `hmp_info_via'
>>> clang-13: error: linker command failed with exit code 1 (use -v to see invocation)
>>>
>>> I have figured that it also fails with this minimal set of configure options
>>> (in addition to the devices CONFIG_* options above):
>>>
>>> $ ../configure --without-default-devices --with-devices-ppc64=ppc64-rh-devices 
>>> --target-list=ppc64-softmmu
>>> $ make -j
>>> ...
>>> /usr/bin/ld: libqemu-ppc64-softmmu.fa.p/monitor_misc.c.o:(.data.rel+0x3228): 
>>> undefined reference to `hmp_info_via'
>>> collect2: error: ld returned 1 exit status
>>>
>>> Since TARGET_PPC is defined when building target ppc64-softmmu, the hmp_info_via 
>>> will be referenced when processing the hmp-commands-info.hx.
>>> However, hmp_info_via implementation resides on hw/misc/mos6522.c, which is built 
>>> only if CONFIG_MOS6522 is defined, as per hw/misc/meson.build.
>>>
>>> If hmp_info_via is generic enough and not device-specific, it could be moved out 
>>> of mos6522.c to somewhere else.
>>>
>>> What do you think?
>>>
>>> [0] 
>>> https://gitlab.com/redhat/centos-stream/rpms/qemu-kvm/-/blob/c9s/qemu-kvm.spec#L686
>>
>> It's probably easier if I post a link to the original thread at 
>> https://lore.kernel.org/all/20220127205405.23499-9-mark.cave-ayland@ilande.co.uk/ 
>> for reference but the main takeaway is:
>>
>> - Device CONFIG_* defines aren't present when building hmp-commands-info.hx
>>
>> - The TARGET_* defines are poisoned in qapi/qapi-commands-misc-target.h
>>
>> - The long-term solution is to implement a DeviceClass function callback that allows
>>    "info debug <foo>" QMP-wrapped monitor commands to be registered dynamically by
>>    devices. But that needs someone with the time and ability to implement it.
>>
>> The compromise was to accept the command wrapped by TARGET_ defines where it is 
>> used, but of course that won't work in this case where you're generating a custom 
>> configuration as above.
>>
>> Certainly QEMU could do better here, but then if you are already patching the build 
>> to generate a custom configuration as above, you might as well just patch out the 
>> relevant part of hmp-commands-info.hx at the same time until proper per-device 
>> HMP/QMP support is added.
> 
> We are not patching the build.  We are just configuring it.

That's not true though: the spec file linked above contains 20 patches to the vanilla 
QEMU source, including feeding custom device lists into the build system via 
https://gitlab.com/redhat/centos-stream/rpms/qemu-kvm/-/blob/c9s/0005-Enable-disable-devices-for-RHEL.patch. 
Perhaps CONFIG_MOS6522 is missing from ppc64-rh-devices?

If you need to generate a build within a short timeframe then patching out the part 
of the build that fails for you is going to be the quickest solution.

> QEMU at tag v6.2.0 works with the exact same configuration.
> QEMU 7.0.0 does not.
> This is a regression in QEMU source code.

I've just tried a plain "./configure --target-list=ppc64-softmmu" build here on my 
x86_64 host using git master and everything builds fine, and of course it passes 
gitlab-CI since that is a pre-requisite for merging. The only thing I can think is 
that your RHEL ppc64 build is being patched to remove the Mac machines which is why 
you see the failure, in which case you should also update the patch to remove the 
part referencing hmp_info_via.

> Is my ideia of moving the hmp_info_via implementation out of mos6522.c an acceptable 
> way to have this fixed in the short-term?

The current solution was agreed after discussions with David and Daniel (the HMP and 
QMP maintainers) so they are the people who can advise you as to the best approach 
here. Unfortunately QEMU changes can involve testing an N x M matrix which gets even 
bigger when different accelerators are involved, so occassionally issues like this 
can still occur.

If you feel strongly that upstream should support this particular RHEL configuration 
then please consider adding it to gitlab-CI so that build issues like this can be 
detected before merge.


ATB,

Mark.