Re: [PATCH v2 00/20] vfio: Add migration pre-copy support and device dirty tracking

["Cédric Le Goater" <clg@redhat.com>]

On 2/23/23 16:07, Avihai Horon wrote:
> 
> On 23/02/2023 12:05, Cédric Le Goater wrote:
>> External email: Use caution opening links or attachments
>>
>>
>> On 2/22/23 21:55, Alex Williamson wrote:
>>>
>>> There are various errors running this through the CI on gitlab.
>>>
>>> This one seems bogus but needs to be resolved regardless:
>>>
>>> https://gitlab.com/alex.williamson/qemu/-/jobs/3817940731
>>> FAILED: libqemu-aarch64-softmmu.fa.p/hw_vfio_common.c.o
>>> 2786s390x-linux-gnu-gcc -m64 -Ilibqemu-aarch64-softmmu.fa.p -I. -I.. -Itarget/arm -I../target/arm -Iqapi -Itrace -Iui -Iui/shader -I/usr/include/pixman-1 -I/usr/include/capstone -I/usr/include/glib-2.0 -I/usr/lib/s390x-linux-gnu/glib-2.0/include -fdiagnostics-color=auto -Wall -Winvalid-pch -Werror -std=gnu11 -O2 -g -isystem /builds/alex.williamson/qemu/linux-headers -isystem linux-headers -iquote . -iquote /builds/alex.williamson/qemu -iquote /builds/alex.williamson/qemu/include -iquote /builds/alex.williamson/qemu/tcg/s390x -pthread -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -fno-strict-aliasing -fno-common -fwrapv -Wundef -Wwrite-strings -Wmissing-prototypes -Wstrict-prototypes -Wredundant-decls -Wold-style-declaration -Wold-style-definition -Wtype-limits -Wformat-security -Wformat-y2k -Winit-self -Wignored-qualifiers -Wempty-body -Wnested-externs -Wendif-labels -Wexpansion-to-defined -Wimplicit-fallthrough=2 
>>> -Wmissing-format-attribute -Wno-missing-include-dirs -Wno-shift-negative-value -Wno-psabi -fstack-protector-strong -fPIE -isystem../linux-headers -isystemlinux-headers -DNEED_CPU_H '-DCONFIG_TARGET="aarch64-softmmu-config-target.h"' '-DCONFIG_DEVICES="aarch64-softmmu-config-devices.h"' -MD -MQ libqemu-aarch64-softmmu.fa.p/hw_vfio_common.c.o -MF libqemu-aarch64-softmmu.fa.p/hw_vfio_common.c.o.d -o libqemu-aarch64-softmmu.fa.p/hw_vfio_common.c.o -c ../hw/vfio/common.c
>>> 2787../hw/vfio/common.c: In function ‘vfio_listener_log_global_start’:
>>> 2788../hw/vfio/common.c:1772:8: error: ‘ret’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
>>> 2789 1772 |     if (ret) {
>>> 2790      |        ^
>>
>>
>> The routine to fix is vfio_devices_start_dirty_page_tracking(). The compiler
>> is doing some inlining.
>>
> I don't think I understand how inlining could cause it.
> Could you elaborate on this?

The compiler reports an error in routine 'vfio_listener_log_global_start'
but the fix should be in 'vfio_devices_start_dirty_page_tracking'. Surely
because the compiler optimization inlines the latter.

> 
> I thought that the compiler just missed the initialization of ret because it happens in the if else statement, and that simply doing "int ret = 0;" would solve it.

Yes. This will work.

Thanks,

C.