ZFS failing to compile inline against 5.12.4-gentoo kernel

[thehaven]

System information

Type	Version/Name
Distribution Name	Gentoo
Distribution Version	17.1
Linux Kernel	5.12.4-gentoo
Architecture	x86_64
ZFS Version	7457b02 (HEAD)
SPL Version

Describe the problem you're observing

Compling ZFS as builtin to the 5.12.4 kernel is failing.

Describe how to reproduce the problem

Compiling ZFS into the kernel using this script:

• https://gist.github.com/thehaven/6946427
  Then compling kernel via make.

GCC version is 11.1.0

Include any warning/errors/backtraces from the system logs

Kernel build error (second run to highlight the issue):

builder /usr/src/linux # make
  CALL    scripts/checksyscalls.sh
  CALL    scripts/atomic/check-atomics.sh
  DESCEND  objtool
  CHK     include/generated/compile.h
  CC      fs/zfs/zfs/../os/linux/zfs/zfs_ioctl_os.o
In file included from <command-line>:
./include/linux/compiler-gcc.h:39:66: error: pasting ")" and "6" does not give a valid preprocessing token
   39 | #define __noretpoline __attribute__((__indirect_branch__("keep")))
      |                                                                  ^
././include/linux/compiler_types.h:59:23: note: in definition of macro ‘___PASTE’
   59 | #define ___PASTE(a,b) a##b
      |                       ^
./include/linux/init.h:201:9: note: in expansion of macro ‘__PASTE’
  201 |         __PASTE(__iid, id))))
      |         ^~~~~~~
./include/linux/init.h:255:17: note: in expansion of macro ‘__initcall_name’
  255 |                 __initcall_name(initcall, __iid, id),           \
      |                 ^~~~~~~~~~~~~~~
./include/linux/init.h:259:9: note: in expansion of macro ‘__unique_initcall’
  259 |         __unique_initcall(fn, id, __sec, __initcall_id(fn))
      |         ^~~~~~~~~~~~~~~~~
././include/linux/compiler_types.h:60:22: note: in expansion of macro ‘___PASTE’
   60 | #define __PASTE(a,b) ___PASTE(a,b)
      |                      ^~~~~~~~
./include/linux/init.h:189:9: note: in expansion of macro ‘__PASTE’
  189 |         __PASTE(__KBUILD_MODNAME,                               \
      |         ^~~~~~~
././include/linux/compiler_types.h:60:22: note: in expansion of macro ‘___PASTE’
   60 | #define __PASTE(a,b) ___PASTE(a,b)
      |                      ^~~~~~~~
./include/linux/init.h:190:9: note: in expansion of macro ‘__PASTE’
  190 |         __PASTE(__,                                             \
      |         ^~~~~~~
././include/linux/compiler_types.h:60:22: note: in expansion of macro ‘___PASTE’
   60 | #define __PASTE(a,b) ___PASTE(a,b)
      |                      ^~~~~~~~
./include/linux/init.h:191:9: note: in expansion of macro ‘__PASTE’
  191 |         __PASTE(__COUNTER__,                                    \
      |         ^~~~~~~
././include/linux/compiler_types.h:60:22: note: in expansion of macro ‘___PASTE’
   60 | #define __PASTE(a,b) ___PASTE(a,b)
      |                      ^~~~~~~~
./include/linux/init.h:192:9: note: in expansion of macro ‘__PASTE’
  192 |         __PASTE(_,                                              \
      |         ^~~~~~~
././include/linux/compiler_types.h:60:22: note: in expansion of macro ‘___PASTE’
   60 | #define __PASTE(a,b) ___PASTE(a,b)
      |                      ^~~~~~~~
./include/linux/init.h:193:9: note: in expansion of macro ‘__PASTE’
  193 |         __PASTE(__LINE__,                                       \
      |         ^~~~~~~
./include/linux/init.h:10:27: note: in expansion of macro ‘__noretpoline’
   10 | #define __noinitretpoline __noretpoline
      |                           ^~~~~~~~~~~~~
./include/linux/init.h:50:74: note: in expansion of macro ‘__noinitretpoline’
   50 | #define __init          __section(".init.text") __cold  __latent_entropy __noinitretpoline
      |                                                                          ^~~~~~~~~~~~~~~~~
././include/linux/compiler_types.h:59:23: note: in expansion of macro ‘__init’
   59 | #define ___PASTE(a,b) a##b
      |                       ^
././include/linux/compiler_types.h:60:22: note: in expansion of macro ‘___PASTE’
   60 | #define __PASTE(a,b) ___PASTE(a,b)
      |                      ^~~~~~~~
./include/linux/init.h:194:9: note: in expansion of macro ‘__PASTE’
  194 |         __PASTE(_, fn))))))
      |         ^~~~~~~
./include/linux/init.h:259:42: note: in expansion of macro ‘__initcall_id’
  259 |         __unique_initcall(fn, id, __sec, __initcall_id(fn))
      |                                          ^~~~~~~~~~~~~
./include/linux/init.h:261:35: note: in expansion of macro ‘___define_initcall’
  261 | #define __define_initcall(fn, id) ___define_initcall(fn, id, .initcall##id)
      |                                   ^~~~~~~~~~~~~~~~~~
./include/linux/init.h:290:41: note: in expansion of macro ‘__define_initcall’
  290 | #define device_initcall(fn)             __define_initcall(fn, 6)
      |                                         ^~~~~~~~~~~~~~~~~
./include/linux/init.h:295:24: note: in expansion of macro ‘device_initcall’
  295 | #define __initcall(fn) device_initcall(fn)
      |                        ^~~~~~~~~~~~~~~
./include/linux/module.h:86:25: note: in expansion of macro ‘__initcall’
   86 | #define module_init(x)  __initcall(x);
      |                         ^~~~~~~~~~
fs/zfs/zfs/../os/linux/zfs/zfs_ioctl_os.c:267:1: note: in expansion of macro ‘module_init’
  267 | module_init(_init);
      | ^~~~~~~~~~~
make[3]: *** [scripts/Makefile.build:271: fs/zfs/zfs/../os/linux/zfs/zfs_ioctl_os.o] Error 1
make[2]: *** [scripts/Makefile.build:514: fs/zfs/zfs] Error 2
make[1]: *** [scripts/Makefile.build:514: fs/zfs] Error 2
make: *** [Makefile:1851: fs] Error 2

[rincebrain]

Hey look, it's #11987 (yes I know the title doesn't look related)