GCC 9.0: ‘init_module’ specifies less restrictive attribute than its target

[tonyhutter]

System information

Type	Version/Name
Distribution Name	Fedora
Distribution Version	30 (rawhide)
Linux Kernel	5.0.0-0.rc3.git0.1.fc30.x86_64
Architecture	x86-64
ZFS Version	master
SPL Version	master

Describe the problem you're observing

The upcoming GCC 9 release adds the -Wmissing-attributes warnings
(enabled by -Wall), which trigger for all the init/cleanup_module
aliases in the kernel (defined by the module_init/exit macros),
ending up being very noisy.

These aliases point to the __init/__exit functions of a module,
which are defined as __cold (among other attributes). However,
the aliases themselves do not have the __cold attribute.

Since the compiler behaves differently when compiling a __cold
function as well as when compiling paths leading to calls
to __cold functions, the warning is trying to point out
the possibly-forgotten attribute in the alias.

https://lore.kernel.org/lkml/20190123173707.GA16603@gmail.com/

This looks like a kernel problem that is being fixed.

Describe how to reproduce the problem

build master in latest updated rawhide

Include any warning/errors/backtraces from the system logs

  CC [M]  /home/hutter/50-kernel/module/spl/spl-generic.o
In file included from /home/hutter/50-kernel/include/spl/sys/sysmacros.h:28,
                 from /home/hutter/50-kernel/module/spl/spl-generic.c:27:
./include/linux/module.h:132:6: warning: ‘init_module’ specifies less restrictive attribute than its target ‘spl_init’: ‘cold’ [-Wmissing-attributes]
  132 |  int init_module(void) __attribute__((alias(#initfn)));
      |      ^~~~~~~~~~~
/home/hutter/50-kernel/module/spl/spl-generic.c:762:1: note: in expansion of macro ‘module_init’
  762 | module_init(spl_init);
      | ^~~~~~~~~~~
/home/hutter/50-kernel/module/spl/spl-generic.c:686:1: note: ‘init_module’ target declared here
  686 | spl_init(void)
      | ^~~~~~~~

[tonyhutter]

I havn't tested it, but I believe this may have been fixed by:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0b999ae3614d09d97a1575936bcee884f912b10e