UBUNTU: SAUCE: modpost: support arbitrary symbol length in modversion

BugLink: https://bugs.launchpad.net/bugs/2007654

Currently modversion uses a fixed size array of size (64 - sizeof(long))
to store symbol names, thus placing a hard limit on length of symbols.
Rust symbols (which encodes crate and module names) can be quite a bit
longer. The length limit in kallsyms is increased to 512 for this reason.

It's a waste of space to simply expand the fixed array size to 512 in
modversion info entries. I therefore make it variably sized, with offset
to the next entry indicated by the initial "next" field.

In addition to supporting longer-than-56/60 byte symbols, this patch also
reduce the size for short symbols by getting rid of excessive 0 paddings.
There are still some zero paddings to ensure "next" and "crc" fields are
properly aligned.

This patch does have a tiny drawback that it makes ".mod.c" files generated
a bit less easy to read, as code like

	"\x08\x00\x00\x00\x78\x56\x34\x12"
	"symbol\0\0"

is generated as opposed to

	{ 0x12345678, "symbol" },

because the structure is now variable-length. But hopefully nobody reads
the generated file :)

Link: b8a94bfb33 ("kallsyms: increase maximum kernel symbol length to 512")
Link: https://github.com/Rust-for-Linux/linux/pull/379

Signed-off-by: Gary Guo <gary@garyguo.net>
(backported from https://lore.kernel.org/lkml/20230111161155.1349375-1-gary@garyguo.net/)
[ fix build error on s390x: always use a variable with TO_NATIVE() ]
[ add dummy NULL entry at the end of the modversion array ]
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>

arch/powerpc/kernel/module_64.c

@@ -347,12 +347,13 @@ static unsigned long get_got_size(const Elf64_Ehdr *hdr,
 static void dedotify_versions(struct modversion_info *vers,
 			      unsigned long size)
 {
-	struct modversion_info *end;
+	struct modversion_info *end = (void *)vers + size;
 
-	for (end = (void *)vers + size; vers < end; vers++)
+	for (; vers < end && vers->next; vers = (void *)vers + vers->next) {
 		if (vers->name[0] == '.') {
 			memmove(vers->name, vers->name+1, strlen(vers->name));
 		}
+	}
 }
 
 /*