kbuild: fix modpost segfault for 64bit mipsel kernel

64bit mips has different r_info layout.  This patch fixes modpost
segfault for 64bit little endian mips kernel.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

scripts/mod/modpost.c

@@ -709,10 +709,17 @@ static void check_sec_ref(struct module *mod, const char *modname,
 		for (rela = start; rela < stop; rela++) {
 			Elf_Rela r;
 			const char *secname;
+			unsigned int r_sym;
 			r.r_offset = TO_NATIVE(rela->r_offset);
-			r.r_info   = TO_NATIVE(rela->r_info);
+			if (hdr->e_ident[EI_CLASS] == ELFCLASS64 &&
+			    hdr->e_machine == EM_MIPS) {
+				r_sym = ELF64_MIPS_R_SYM(rela->r_info);
+				r_sym = TO_NATIVE(r_sym);
+			} else {
+				r_sym = ELF_R_SYM(TO_NATIVE(rela->r_info));
+			}
 			r.r_addend = TO_NATIVE(rela->r_addend);
-			sym = elf->symtab_start + ELF_R_SYM(r.r_info);
+			sym = elf->symtab_start + r_sym;
 			/* Skip special sections */
 			if (sym->st_shndx >= SHN_LORESERVE)
 				continue;

scripts/mod/modpost.h

@@ -39,6 +39,25 @@
 #define ELF_R_TYPE  ELF64_R_TYPE
 #endif
 
+/* The 64-bit MIPS ELF ABI uses an unusual reloc format. */
+typedef struct
+{
+  Elf32_Word    r_sym;		/* Symbol index */
+  unsigned char r_ssym;		/* Special symbol for 2nd relocation */
+  unsigned char r_type3;	/* 3rd relocation type */
+  unsigned char r_type2;	/* 2nd relocation type */
+  unsigned char r_type1;	/* 1st relocation type */
+} _Elf64_Mips_R_Info;
+
+typedef union
+{
+  Elf64_Xword	r_info_number;
+  _Elf64_Mips_R_Info r_info_fields;
+} _Elf64_Mips_R_Info_union;
+
+#define ELF64_MIPS_R_SYM(i) \
+  ((__extension__ (_Elf64_Mips_R_Info_union)(i)).r_info_fields.r_sym)
+
 #if KERNEL_ELFDATA != HOST_ELFDATA
 
 static inline void __endian(const void *src, void *dest, unsigned int size)