modpost: remove broken calculation of exception_table_entry size

modpost: remove broken calculation of exception_table_entry size

BugLink: https://bugs.launchpad.net/bugs/2034469
[ Upstream commit d0acc76a49aa917c1a455d11d32d34a01e8b2835 ]

find_extable_entry_size() is completely broken. It has awesome comments
about how to calculate sizeof(struct exception_table_entry).

It was based on these assumptions:

  - struct exception_table_entry has two fields
  - both of the fields have the same size

Then, we came up with this equation:

  (offset of the second field) * 2 == (size of struct)

It was true for all architectures when commit 52dc0595d540 ("modpost:
handle relocations mismatch in __ex_table.") was applied.

Our mathematics broke when commit 548acf19234d ("x86/mm: Expand the
exception table logic to allow new handling options") introduced the
third field.

Now, the definition of exception_table_entry is highly arch-dependent.

For x86, sizeof(struct exception_table_entry) is apparently 12, but
find_extable_entry_size() sets extable_entry_size to 8.

I could fix it, but I do not see much value in this code.

extable_entry_size is used just for selecting a slightly different
error message.

If the first field ("insn") references to a non-executable section,

    The relocation at %s+0x%lx references
    section "%s" which is not executable, IOW
    it is not possible for the kernel to fault
    at that address.  Something is seriously wrong
    and should be fixed.

If the second field ("fixup") references to a non-executable section,

    The relocation at %s+0x%lx references
    section "%s" which is not executable, IOW
    the kernel will fault if it ever tries to
    jump to it.  Something is seriously wrong
    and should be fixed.

Merge the two error messages rather than adding even more complexity.

Change fatal() to error() to make it continue running and catch more
possible errors.

Fixes: 548acf19234d ("x86/mm: Expand the exception table logic to allow new handling options")
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>