modpost: Ignore relaxation and alignment marker relocs on LoongArch

With recent trunk versions of binutils and gcc, alignment directives are
represented with R_LARCH_ALIGN relocs on LoongArch, which is necessary
for the linker to maintain alignment requirements during its relaxation
passes. And even though the kernel is built with relaxation disabled, so
far a small number of R_LARCH_RELAX marker relocs are still emitted as
part of la.* pseudo instructions in assembly. These two kinds of relocs
do not refer to symbols, which can trip up modpost's section mismatch
checks, because the r_offset of said relocs can be zero or any other
meaningless value, eventually leading to a `from == NULL` condition in
default_mismatch_handler and SIGSEGV.

As the two kinds of relocs are not concerned with symbols, just ignore
them for section mismatch check purposes.
Signed-off-by: WANG Xuerui <git@xen0n.name>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

scripts/mod/modpost.c

@@ -1346,6 +1346,14 @@ static Elf_Addr addend_mips_rel(uint32_t *location, unsigned int r_type)
 #define R_LARCH_SUB32		55
 #endif
 
+#ifndef R_LARCH_RELAX
+#define R_LARCH_RELAX		100
+#endif
+
+#ifndef R_LARCH_ALIGN
+#define R_LARCH_ALIGN		102
+#endif
+
 static void get_rel_type_and_sym(struct elf_info *elf, uint64_t r_info,
 				 unsigned int *r_type, unsigned int *r_sym)
 {
@@ -1400,9 +1408,16 @@ static void section_rela(struct module *mod, struct elf_info *elf,
 				continue;
 			break;
 		case EM_LOONGARCH:
-			if (!strcmp("__ex_table", fromsec) &&
-			    r_type == R_LARCH_SUB32)
+			switch (r_type) {
+			case R_LARCH_SUB32:
+				if (!strcmp("__ex_table", fromsec))
+					continue;
+				break;
+			case R_LARCH_RELAX:
+			case R_LARCH_ALIGN:
+				/* These relocs do not refer to symbols */
 				continue;
+			}
 			break;
 		}