Just updated to the pre-release Fedora 30 (Rawhide) on the test system, and tried out the new version of GCC:

$ gcc --version
gcc (GCC) 9.0.1 20190209 (Red Hat 9.0.1-0.4)

Kernel 5.0-rc7 compiled successfully, and runs OK.    As expected, there were quite a lot of compiler ‘warnings’:

.......................
CC net/ipv4/proc.o
CC drivers/hid/hid-samsung.o
CC net/ipv4/fib_rules.o
CC drivers/hid/hid-sunplus.o
fs/xfs/xfs_ioctl32.c: In function ‘xfs_ioctl32_bstat_copyin’:
fs/xfs/xfs_ioctl32.c:141:50: warning: taking address of packed member of ‘struct compat_xfs_bstat’ may result in an unaligned pointer value [-Waddress-of-packed-member]
141 | xfs_ioctl32_bstime_copyin(&bstat->bs_atime, &bstat32->bs_atime) ||
| ^~~~~~~~~~~~~~~~~~
fs/xfs/xfs_ioctl32.c:142:50: warning: taking address of packed member of ‘struct compat_xfs_bstat’ may result in an unaligned pointer value [-Waddress-of-packed-member]
142 | xfs_ioctl32_bstime_copyin(&bstat->bs_mtime, &bstat32->bs_mtime) ||
| ^~~~~~~~~~~~~~~~~~
fs/xfs/xfs_ioctl32.c:143:50: warning: taking address of packed member of ‘struct compat_xfs_bstat’ may result in an unaligned pointer value [-Waddress-of-packed-member]
143 | xfs_ioctl32_bstime_copyin(&bstat->bs_ctime, &bstat32->bs_ctime) ||
| ^~~~~~~~~~~~~~~~~~
fs/xfs/xfs_ioctl32.c: In function ‘xfs_bulkstat_one_fmt_compat’:
fs/xfs/xfs_ioctl32.c:196:30: warning: taking address of packed member of ‘struct compat_xfs_bstat’ may result in an unaligned pointer value [-Waddress-of-packed-member]
196 | xfs_bstime_store_compat(&p32->bs_atime, &buffer->bs_atime) ||
| ^~~~~~~~~~~~~~
fs/xfs/xfs_ioctl32.c:197:30: warning: taking address of packed member of ‘struct compat_xfs_bstat’ may result in an unaligned pointer value [-Waddress-of-packed-member]
197 | xfs_bstime_store_compat(&p32->bs_mtime, &buffer->bs_mtime) ||
| ^~~~~~~~~~~~~~
fs/xfs/xfs_ioctl32.c:198:30: warning: taking address of packed member of ‘struct compat_xfs_bstat’ may result in an unaligned pointer value [-Waddress-of-packed-member]
198 | xfs_bstime_store_compat(&p32->bs_ctime, &buffer->bs_ctime) ||
| ^~~~~~~~~~~~~~
fs/xfs/xfs_ioctl32.c: In function ‘xfs_compat_attrlist_by_handle’:
fs/xfs/xfs_ioctl32.c:385:51: warning: taking address of packed member of ‘struct compat_xfs_fsop_attrlist_handlereq’ may result in an unaligned pointer value [-Waddress-of-packed-member]
385 | dentry = xfs_compat_handlereq_to_dentry(parfilp, &al_hreq.hreq);
| ^~~~~~~~~~~~~
fs/xfs/xfs_ioctl32.c:394:37: warning: taking address of packed member of ‘struct compat_xfs_fsop_attrlist_handlereq’ may result in an unaligned pointer value [-Waddress-of-packed-member]
394 | cursor = (attrlist_cursor_kern_t *)&al_hreq.pos;
| ^~~~~~~~~~~~
CC net/ipv4/ipmr.o
CC drivers/hid/hid-topseed.o
LD [M] fs/xfs/xfs.o
CC [M] drivers/gpu/drm/i915/i915_gem_object.o
CC fs/binfmt_elf.o
...................

Next, I tried the VMware 15.0.2 vmmon/vmnet drivers, patched for Kernel 5.0…  vmnet actually compiled cleanly, but vmmon threw a lot of warnings, although the compilation completed OK:

............................
/home/rgadsdon/kernel/vmware15-kernel50/vmware-host-modules/vmmon-only/./include/x86desc.h: In function ‘Desc64_EqualIgnoreAccessed’:
/home/rgadsdon/kernel/vmware15-kernel50/vmware-host-modules/vmmon-only/./include/x86desc.h:155:4: warning: converting a packed ‘Descriptor64’ {aka ‘const struct Descriptor64’} pointer (alignment 1) to a ‘Descriptor64Union’ {aka ‘const union <anonymous>’} pointer (alignment 8) may result in an unaligned pointer value [-Waddress-of-packed-member]
155 | const Descriptor64Union *du1 = (const Descriptor64Union*) d1;
| ^~~~~
/home/rgadsdon/kernel/vmware15-kernel50/vmware-host-modules/vmmon-only/./include/x86desc.h:156:4: warning: converting a packed ‘Descriptor64’ {aka ‘const struct Descriptor64’} pointer (alignment 1) to a ‘Descriptor64Union’ {aka ‘const union <anonymous>’} pointer (alignment 8) may result in an unaligned pointer value [-Waddress-of-packed-member]
156 | const Descriptor64Union *du2 = (const Descriptor64Union*) d2;
| ^~~~~
CC [M] /home/rgadsdon/kernel/vmware15-kernel50/vmware-host-modules/vmmon-only/bootstrap/monLoader.o
CC [M] /home/rgadsdon/kernel/vmware15-kernel50/vmware-host-modules/vmmon-only/bootstrap/vmmblob.o
In file included from /home/rgadsdon/kernel/vmware15-kernel50/vmware-host-modules/vmmon-only/./include/modulecall.h:34,
from /home/rgadsdon/kernel/vmware15-kernel50/vmware-host-modules/vmmon-only/./common/vmx86.h:33,
from /home/rgadsdon/kernel/vmware15-kernel50/vmware-host-modules/vmmon-only/./common/hostif.h:32,
from /home/rgadsdon/kernel/vmware15-kernel50/vmware-host-modules/vmmon-only/bootstrap/vmmblob.c:30:
/home/rgadsdon/kernel/vmware15-kernel50/vmware-host-modules/vmmon-only/./include/x86desc.h: In function ‘Desc64_EqualIgnoreAccessed’:
/home/rgadsdon/kernel/vmware15-kernel50/vmware-host-modules/vmmon-only/./include/x86desc.h:155:4: warning: converting a packed ‘Descriptor64’ {aka ‘const struct Descriptor64’} pointer (alignment 1) to a ‘Descriptor64Union’ {aka ‘const union <anonymous>’} pointer (alignment 8) may result in an unaligned pointer value [-Waddress-of-packed-member]
155 | const Descriptor64Union *du1 = (const Descriptor64Union*) d1;
| ^~~~~
/home/rgadsdon/kernel/vmware15-kernel50/vmware-host-modules/vmmon-only/./include/x86desc.h:156:4: warning: converting a packed ‘Descriptor64’ {aka ‘const struct Descriptor64’} pointer (alignment 1) to a ‘Descriptor64Union’ {aka ‘const union <anonymous>’} pointer (alignment 8) may result in an unaligned pointer value [-Waddress-of-packed-member]
.........................

The latest NVIDIA driver – 418.30 – compiled successfully, with just one warning:

........................
/home/rgadsdon/kernel/NVIDIA-Linux-x86_64-418.30/kernel/nvidia-uvm/uvm8_mmu.c: In function ‘uvm_page_tree_put_ptes_async’:
/home/rgadsdon/kernel/NVIDIA-Linux-x86_64-418.30/kernel/nvidia-uvm/uvm8_mmu.c:693:5: warning: ‘invalidate_depth’ may be used uninitialized in this function [-Wmaybe-uninitialized]
693 | tree->gpu->host_hal->tlb_invalidate_all(&push,
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
694 | uvm_page_tree_pdb(tree)->addr,
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
695 | invalidate_depth,
| ~~~~~~~~~~~~~~~~~
696 | membar_after_invalidate);
| ~~~~~~~~~~~~~~~~~~~~~~~~
.........................

This Fedora version is not yet ready for real use, as a lot of the off-distro multimedia applications (from rpmfusion..etc.) are not yet available..

Robert Gadsdon.   February 21, 2019.