Not buildable on i686

[mikhailnov]

Latest HEAD - https://github.com/umlaeute/v4l2loopback/commit/9ba7e294ea6f45410a15f192381d4918e8df4f02 - is buildable on x86_64 and aarch64, but is not on i686 (x86_32):

ERROR: modpost: "__moddi3" [/root/v4l2loopback/v4l2loopback.ko] undefined!

I do not see where __moddi3 gets from.

Actually nobody is going to use it on i686, so it is not a big problem.

Bigger log:

# make V=1
Building v4l2-loopback driver...
make -C /lib/modules/`uname -r`/build M=/root/v4l2loopback KCPPFLAGS="" modules
make[1]: вход в каталог «/usr/src/linux-6.1.38-generic-1rosa2021.1-i686»
make -f ./scripts/Makefile.build obj=/root/v4l2loopback need-builtin=1 need-modorder=1 
  gcc -Wp,-MMD,/root/v4l2loopback/.v4l2loopback.o.d -nostdinc -I./arch/x86/include -I./arch/x86/include/generated  -I./include -I./arch/x86/include/uapi -I./arch/x86/include/generated/uapi -I./include/uapi -I./include/generated/uapi -include ./include/linux/compiler-version.h -include ./include/linux/kconfig.h -include ./include/linux/compiler_types.h -D__KERNEL__ -fmacro-prefix-map=./= -Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE -Werror=implicit-function-declaration -Werror=implicit-int -Werror=return-type -Wno-format-security -std=gnu11 -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx -fcf-protection=none -m32 -msoft-float -mregparm=3 -freg-struct-return -fno-pic -mpreferred-stack-boundary=2 -march=i686 -mtune=generic -Wa,-mtune=generic32 -ffreestanding -mstack-protector-guard-reg=fs -mstack-protector-guard-symbol=__stack_chk_guard -Wno-sign-compare -fno-asynchronous-unwind-tables -mindirect-branch=thunk-extern -mindirect-branch-register -fno-jump-tables -fno-delete-null-pointer-checks -Wno-frame-address -Wno-format-truncation -Wno-format-overflow -Wno-address-of-packed-member -O2 -fno-allow-store-data-races -Wframe-larger-than=2048 -fstack-protector-strong -Wno-main -Wno-unused-but-set-variable -Wno-unused-const-variable -fno-omit-frame-pointer -fno-optimize-sibling-calls -fno-stack-clash-protection -fzero-call-used-regs=used-gpr -pg -mrecord-mcount -mfentry -DCC_USING_FENTRY -Wdeclaration-after-statement -Wvla -Wno-pointer-sign -Wcast-function-type -Wno-stringop-truncation -Wno-stringop-overflow -Wno-restrict -Wno-maybe-uninitialized -Wno-array-bounds -Wno-alloc-size-larger-than -Wimplicit-fallthrough=5 -fno-strict-overflow -fno-stack-check -fconserve-stack -Werror=date-time -Werror=incompatible-pointer-types -Werror=designated-init -Wno-packed-not-aligned -g -gdwarf-4  -DMODULE  -DKBUILD_BASENAME='"v4l2loopback"' -DKBUILD_MODNAME='"v4l2loopback"' -D__KBUILD_MODNAME=kmod_v4l2loopback -c -o /root/v4l2loopback/v4l2loopback.o /root/v4l2loopback/v4l2loopback.c  
  ./scripts/check-local-export /root/v4l2loopback/v4l2loopback.o
  if nm /root/v4l2loopback/v4l2loopback.o 2>/dev/null | grep -q __ksymtab; then gcc -E -D__GENKSYMS__ -Wp,-MMD,/root/v4l2loopback/.v4l2loopback.o.d -nostdinc -I./arch/x86/include -I./arch/x86/include/generated  -I./include -I./arch/x86/include/uapi -I./arch/x86/include/generated/uapi -I./include/uapi -I./include/generated/uapi -include ./include/linux/compiler-version.h -include ./include/linux/kconfig.h -include ./include/linux/compiler_types.h -D__KERNEL__ -fmacro-prefix-map=./= -Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE -Werror=implicit-function-declaration -Werror=implicit-int -Werror=return-type -Wno-format-security -std=gnu11 -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx -fcf-protection=none -m32 -msoft-float -mregparm=3 -freg-struct-return -fno-pic -mpreferred-stack-boundary=2 -march=i686 -mtune=generic -Wa,-mtune=generic32 -ffreestanding -mstack-protector-guard-reg=fs -mstack-protector-guard-symbol=__stack_chk_guard -Wno-sign-compare -fno-asynchronous-unwind-tables -mindirect-branch=thunk-extern -mindirect-branch-register -fno-jump-tables -fno-delete-null-pointer-checks -Wno-frame-address -Wno-format-truncation -Wno-format-overflow -Wno-address-of-packed-member -O2 -fno-allow-store-data-races -Wframe-larger-than=2048 -fstack-protector-strong -Wno-main -Wno-unused-but-set-variable -Wno-unused-const-variable -fno-omit-frame-pointer -fno-optimize-sibling-calls -fno-stack-clash-protection -fzero-call-used-regs=used-gpr -pg -mrecord-mcount -mfentry -DCC_USING_FENTRY -Wdeclaration-after-statement -Wvla -Wno-pointer-sign -Wcast-function-type -Wno-stringop-truncation -Wno-stringop-overflow -Wno-restrict -Wno-maybe-uninitialized -Wno-array-bounds -Wno-alloc-size-larger-than -Wimplicit-fallthrough=5 -fno-strict-overflow -fno-stack-check -fconserve-stack -Werror=date-time -Werror=incompatible-pointer-types -Werror=designated-init -Wno-packed-not-aligned -g -gdwarf-4  -DMODULE  -DKBUILD_BASENAME='"v4l2loopback"' -DKBUILD_MODNAME='"v4l2loopback"' -D__KBUILD_MODNAME=kmod_v4l2loopback /root/v4l2loopback/v4l2loopback.c | scripts/genksyms/genksyms   -r /dev/null >> /root/v4l2loopback/.v4l2loopback.o.cmd; fi
  {   echo /root/v4l2loopback/v4l2loopback.ko; :; } > /root/v4l2loopback/modules.order
sh ./scripts/modules-check.sh /root/v4l2loopback/modules.order
make -f ./scripts/Makefile.modpost
   sed 's/ko$/o/'  /root/v4l2loopback/modules.order | scripts/mod/modpost -m -a    -o /root/v4l2loopback/Module.symvers -e -i Module.symvers -T - 
ERROR: modpost: "__moddi3" [/root/v4l2loopback/v4l2loopback.ko] undefined!

I'm not sure that the problem is in v4l2loopback.

[mikhailnov]

The latest commit on which a 32 bit kernel module for kernel 6.1 is buildable is b92e9ce7cccd30cd28743a3fe57eb7827909aeab

[mikhailnov]

So, commit 9f512816dfad3beb1d329bcb1d5955f6c5ddda99 broke 32 bit

[pfactum]

Does this:

diff --git a/drivers/media/v4l2-core/v4l2loopback.c b/drivers/media/v4l2-core/v4l2loopback.c
index 4659bdf7ebea..012bbcb11173 100644
--- a/drivers/media/v4l2-core/v4l2loopback.c
+++ b/drivers/media/v4l2-core/v4l2loopback.c
@@ -1541,7 +1541,7 @@ static int vidioc_reqbufs(struct file *file, void *fh,
 {
    struct v4l2_loopback_device *dev;
    struct v4l2_loopback_opener *opener;
-   int i;
+   int i, t;
    MARK();

    dev = v4l2loopback_getdevice(file);
@@ -1594,7 +1594,8 @@ static int vidioc_reqbufs(struct file *file, void *fh,

            /* after we update dev->used_buffers, buffers in outbufs_list will
             * correspond to dev->write_position + [0;b->count-1] range */
-           i = dev->write_position % b->count;
+           t = dev->write_position;
+           i = do_div(t, b->count);
            list_for_each_entry(pos, &dev->outbufs_list,
                        list_head) {
                dev->bufpos2index[i % b->count] =

fix the issue?

[mikhailnov]

No, it did not fix i686 builds

https://abf.io/build_lists/4681832 https://file-store.rosalinux.ru/api/v1/file_stores/7171b89d5a59138e3053993e5dc41928b58c60ce.log?show=true DEBUG: ERROR: modpost: "__moddi3" [/builddir/build/BUILD/v4l2loopback-9ba7e294ea6f45410a15f192381d4918e8df4f02/v4l2loopback.ko] undefined!

[pfactum]

Oh, sorry, I've just realised you are from Muscovy. Given you kill people in Ukraine, I'll not help you further.

Good luck.

[mikhailnov]

Буду рад Вашему возвращению в здравоумие, если это когда-нибудь случится 🙂

[umlaeute]

@pfactum please stop this. you are free to help or not help whomever you like, but please keep your reasons for yourself when you are posting on this issue tracker.

[mikhailnov]

Thanks for the fix.