Re: [PATCH RFC v2 00/13] virtio: introduce support for GSO over UDP tunnel

[Paolo Abeni <pabeni@redhat.com>]

On 7/14/25 10:43 AM, Lei Yang wrote:
> Does the compile of this series of patches require support for a
> special kernel environment? I hit a compile issue after applied you
> patches:
> [1440/2928] Compiling C object libsystem.a.p/hw_virtio_vhost.c.o
> FAILED: libsystem.a.p/hw_virtio_vhost.c.o
> cc -m64 -Ilibsystem.a.p -I. -I.. -Isubprojects/dtc/libfdt
> -I../subprojects/dtc/libfdt -Isubprojects/libvduse
> -I../subprojects/libvduse -Iui -Iqapi -Itrace -Iui/shader
> -I/usr/include/pixman-1 -I/usr/include/glib-2.0
> -I/usr/lib64/glib-2.0/include -I/usr/include/libmount
> -I/usr/include/blkid -I/usr/include/sysprof-6
> -I/usr/include/gio-unix-2.0 -I/usr/include/slirp
> -fdiagnostics-color=auto -Wall -Winvalid-pch -Werror -std=gnu11 -O0 -g
> -fstack-protector-strong -Wempty-body -Wendif-labels
> -Wexpansion-to-defined -Wformat-security -Wformat-y2k
> -Wignored-qualifiers -Wimplicit-fallthrough=2 -Winit-self
> -Wmissing-format-attribute -Wmissing-prototypes -Wnested-externs
> -Wold-style-declaration -Wold-style-definition -Wredundant-decls
> -Wshadow=local -Wstrict-prototypes -Wtype-limits -Wundef -Wvla
> -Wwrite-strings -Wno-missing-include-dirs -Wno-psabi
> -Wno-shift-negative-value -isystem
> /mnt/tests/distribution/command/qemu/linux-headers -isystem
> linux-headers -iquote . -iquote /mnt/tests/distribution/command/qemu
> -iquote /mnt/tests/distribution/command/qemu/include -iquote
> /mnt/tests/distribution/command/qemu/host/include/x86_64 -iquote
> /mnt/tests/distribution/command/qemu/host/include/generic -iquote
> /mnt/tests/distribution/command/qemu/tcg/i386 -pthread -mcx16 -msse2
> -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE
> -fno-strict-aliasing -fno-common -fwrapv -ftrivial-auto-var-init=zero
> -fzero-call-used-regs=used-gpr -fPIE -DWITH_GZFILEOP -DCONFIG_SOFTMMU
> -DCOMPILING_SYSTEM_VS_USER -MD -MQ libsystem.a.p/hw_virtio_vhost.c.o
> -MF libsystem.a.p/hw_virtio_vhost.c.o.d -o
> libsystem.a.p/hw_virtio_vhost.c.o -c ../hw/virtio/vhost.c
> ../hw/virtio/vhost.c: In function ‘vhost_dev_set_features’:
> ../hw/virtio/vhost.c:38:9: error: ‘r’ may be used uninitialized
> [-Werror=maybe-uninitialized]
>    38 |         error_report(fmt ": %s (%d)", ## __VA_ARGS__, \
>       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    39 |                      strerror(-retval), -retval); \
>       |                      ~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ../hw/virtio/vhost.c:1006:9: note: in expansion of macro ‘VHOST_OPS_DEBUG’
>  1006 |         VHOST_OPS_DEBUG(r, "extended features without device support");
>       |         ^~~~~~~~~~~~~~~
> ../hw/virtio/vhost.c:989:9: note: ‘r’ was declared here
>   989 |     int r;
>       |         ^
> cc1: all warnings being treated as errors
> ninja: build stopped: subcommand failed.
> make[1]: *** [Makefile:168: run-ninja] Error 1
> make[1]: Leaving directory '/mnt/tests/distribution/command/qemu/build'
> make[1]: Entering directory '/mnt/tests/distribution/command/qemu/build'
> [1/1493] Generating subprojects/dtc/version_gen.h with a custom command
> [2/1493] Generating qemu-version.h with a custom command (wrapped by
> meson to capture output)
> [3/1492] Compiling C object libsystem.a.p/hw_virtio_vhost.c.o
> FAILED: libsystem.a.p/hw_virtio_vhost.c.o
> cc -m64 -Ilibsystem.a.p -I. -I.. -Isubprojects/dtc/libfdt
> -I../subprojects/dtc/libfdt -Isubprojects/libvduse
> -I../subprojects/libvduse -Iui -Iqapi -Itrace -Iui/shader
> -I/usr/include/pixman-1 -I/usr/include/glib-2.0
> -I/usr/lib64/glib-2.0/include -I/usr/include/libmount
> -I/usr/include/blkid -I/usr/include/sysprof-6
> -I/usr/include/gio-unix-2.0 -I/usr/include/slirp
> -fdiagnostics-color=auto -Wall -Winvalid-pch -Werror -std=gnu11 -O0 -g
> -fstack-protector-strong -Wempty-body -Wendif-labels
> -Wexpansion-to-defined -Wformat-security -Wformat-y2k
> -Wignored-qualifiers -Wimplicit-fallthrough=2 -Winit-self
> -Wmissing-format-attribute -Wmissing-prototypes -Wnested-externs
> -Wold-style-declaration -Wold-style-definition -Wredundant-decls
> -Wshadow=local -Wstrict-prototypes -Wtype-limits -Wundef -Wvla
> -Wwrite-strings -Wno-missing-include-dirs -Wno-psabi
> -Wno-shift-negative-value -isystem
> /mnt/tests/distribution/command/qemu/linux-headers -isystem
> linux-headers -iquote . -iquote /mnt/tests/distribution/command/qemu
> -iquote /mnt/tests/distribution/command/qemu/include -iquote
> /mnt/tests/distribution/command/qemu/host/include/x86_64 -iquote
> /mnt/tests/distribution/command/qemu/host/include/generic -iquote
> /mnt/tests/distribution/command/qemu/tcg/i386 -pthread -mcx16 -msse2
> -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE
> -fno-strict-aliasing -fno-common -fwrapv -ftrivial-auto-var-init=zero
> -fzero-call-used-regs=used-gpr -fPIE -DWITH_GZFILEOP -DCONFIG_SOFTMMU
> -DCOMPILING_SYSTEM_VS_USER -MD -MQ libsystem.a.p/hw_virtio_vhost.c.o
> -MF libsystem.a.p/hw_virtio_vhost.c.o.d -o
> libsystem.a.p/hw_virtio_vhost.c.o -c ../hw/virtio/vhost.c
> ../hw/virtio/vhost.c: In function ‘vhost_dev_set_features’:
> ../hw/virtio/vhost.c:38:9: error: ‘r’ may be used uninitialized
> [-Werror=maybe-uninitialized]
>    38 |         error_report(fmt ": %s (%d)", ## __VA_ARGS__, \
>       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    39 |                      strerror(-retval), -retval); \
>       |                      ~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ../hw/virtio/vhost.c:1006:9: note: in expansion of macro ‘VHOST_OPS_DEBUG’
>  1006 |         VHOST_OPS_DEBUG(r, "extended features without device support");
>       |         ^~~~~~~~~~~~~~~
> ../hw/virtio/vhost.c:989:9: note: ‘r’ was declared here
>   989 |     int r;
>       |         ^
> cc1: all warnings being treated as errors
> ninja: build stopped: subcommand failed.
> make[1]: *** [Makefile:168: run-ninja] Error 1
> make[1]: Leaving directory '/mnt/tests/distribution/command/qemu/build'

Thank you for reporting the problem.

No special kernel requirement to build the series, the above is just a
gross mistake on my side in patch 7/13. If you want to test the series,
please apply incrementally the following diff.

What baffles me is that gcc 14.3.1 and 11.5.0 are not raising the
warning (that looks legit/correct) here.

I'll fix the above in the next revision.

Note that you need a running kernel based on current net-next tree in
both the hypervisor and the guest to actually leverage the new feature.

Thanks,

Paolo
---
diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 2eee9b0886..c4eab5ce08 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -1003,8 +1003,8 @@ static int vhost_dev_set_features(struct vhost_dev
*dev,

     if (virtio_features_use_extended(features) &&
         !dev->vhost_ops->vhost_set_features_ex) {
-        VHOST_OPS_DEBUG(r, "extended features without device support");
         r = -EINVAL;
+        VHOST_OPS_DEBUG(r, "extended features without device support");
         goto out;
     }