kbuild: make better section mismatch reports on i386, arm and mips

On i386, ARM and MIPS, warn_sec_mismatch() sometimes fails to show
usefull symbol name.  This is because empty 'refsym' due to 0 r_addend
value.  This patch is to adjust r_addend value, consulting with
apply_relocate() routine in kernel code.

Without this patch:
  MODPOST vmlinux
WARNING: init/built-in.o - Section mismatch: reference to .init.text: from .text between 'rest_init' (at offset 0xf4) and 'try_name'
WARNING: mm/built-in.o - Section mismatch: reference to .init.text: from .text between 'kmem_cache_create' (at offset 0x18a39) and 'cache_reap'
WARNING: mm/built-in.o - Section mismatch: reference to .init.text: from .text between 'kmem_cache_create' (at offset 0x18a6b) and 'cache_reap'

With this patch:
  MODPOST vmlinux
WARNING: mm/built-in.o - Section mismatch: reference to .init.text:set_up_list3s from .text between 'kmem_cache_create' (at offset 0x18a39) and 'cache_reap'
WARNING: mm/built-in.o - Section mismatch: reference to .init.text:set_up_list3s from .text between 'kmem_cache_create' (at offset 0x18a6b) and 'cache_reap'

Now modpost can detect "kernel_init" name (and whitelist it) and show
"set_up_list3s" name.

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

2 files changed, 82 insertions, 0 deletions

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 2fcdbc7a1ee5..ce7e0d17bae2 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -384,6 +384,7 @@ static int parse_elf(struct elf_info *info, const char *filename)
                 sechdrs[i].sh_size   = TO_NATIVE(sechdrs[i].sh_size);
                 sechdrs[i].sh_link   = TO_NATIVE(sechdrs[i].sh_link);
                 sechdrs[i].sh_name   = TO_NATIVE(sechdrs[i].sh_name);
+                sechdrs[i].sh_info   = TO_NATIVE(sechdrs[i].sh_info);
         }
         /* Find symbol table. */
         for (i = 1; i < hdr->e_shnum; i++) {
@@ -773,6 +774,8 @@ static Elf_Sym *find_elf_symbol(struct elf_info *elf, Elf_Addr addr,
         for (sym = elf->symtab_start; sym < elf->symtab_stop; sym++) {
                 if (sym->st_shndx != relsym->st_shndx)
                         continue;
+                if (ELF_ST_TYPE(sym->st_info) == STT_SECTION)
+                        continue;
                 if (sym->st_value == addr)
                         return sym;
         }
@@ -910,6 +913,68 @@ static void warn_sec_mismatch(const char *modname, const char *fromsec,
         }
 }
 
+static void addend_386_rel(struct elf_info *elf, int section, Elf_Rela *r)
+{
+        Elf_Shdr *sechdrs = elf->sechdrs;
+        unsigned int r_typ;
+        unsigned int *location;
+
+        r_typ = ELF_R_TYPE(r->r_info);
+        location = (void *)elf->hdr +
+                sechdrs[sechdrs[section].sh_info].sh_offset + r->r_offset;
+        switch (r_typ) {
+        case R_386_32:
+                r->r_addend = TO_NATIVE(*location);
+                break;
+        case R_386_PC32:
+                r->r_addend = TO_NATIVE(*location) + 4;
+                break;
+        }
+}
+
+static void addend_arm_rel(struct elf_info *elf, int section, Elf_Rela *r)
+{
+        Elf_Shdr *sechdrs = elf->sechdrs;
+        unsigned int r_typ;
+        unsigned int *location;
+
+        r_typ = ELF_R_TYPE(r->r_info);
+        location = (void *)elf->hdr +
+                sechdrs[sechdrs[section].sh_info].sh_offset + r->r_offset;
+        switch (r_typ) {
+        case R_ARM_ABS32:
+                r->r_addend = TO_NATIVE(*location);
+                break;
+        case R_ARM_PC24:
+                r->r_addend = ((TO_NATIVE(*location) & 0x00ffffff) << 2) + 8;
+                break;
+        }
+}
+
+static int addend_mips_rel(struct elf_info *elf, int section, Elf_Rela *r)
+{
+        Elf_Shdr *sechdrs = elf->sechdrs;
+        unsigned int r_typ;
+        unsigned int *location;
+        unsigned int inst;
+
+        r_typ = ELF_R_TYPE(r->r_info);
+        if (r_typ == R_MIPS_HI16)
+                return 1;       /* skip this */
+        location = (void *)elf->hdr +
+                sechdrs[sechdrs[section].sh_info].sh_offset + r->r_offset;
+        inst = TO_NATIVE(*location);
+        switch (r_typ) {
+        case R_MIPS_LO16:
+                r->r_addend = ((inst & 0xffff) ^ 0x8000) - 0x8000;
+                break;
+        case R_MIPS_26:
+                r->r_addend = (inst & 0x03ffffff) << 2;
+                break;
+        }
+        return 0;
+}
+
 /**
  * A module includes a number of sections that are discarded
  * either when loaded or when used as built-in.
@@ -953,8 +1018,11 @@ static void check_sec_ref(struct module *mod, const char *modname,
                                 r.r_offset = TO_NATIVE(rela->r_offset);
 #if KERNEL_ELFCLASS == ELFCLASS64
                                 if (hdr->e_machine == EM_MIPS) {
+                                        unsigned int r_typ;
                                         r_sym = ELF64_MIPS_R_SYM(rela->r_info);
                                         r_sym = TO_NATIVE(r_sym);
+                                        r_typ = ELF64_MIPS_R_TYPE(rela->r_info);
+                                        r.r_info = ELF64_R_INFO(r_sym, r_typ);
                                 } else {
                                         r.r_info = TO_NATIVE(rela->r_info);
                                         r_sym = ELF_R_SYM(r.r_info);
@@ -987,8 +1055,11 @@ static void check_sec_ref(struct module *mod, const char *modname,
                                 r.r_offset = TO_NATIVE(rel->r_offset);
 #if KERNEL_ELFCLASS == ELFCLASS64
                                 if (hdr->e_machine == EM_MIPS) {
+                                        unsigned int r_typ;
                                         r_sym = ELF64_MIPS_R_SYM(rel->r_info);
                                         r_sym = TO_NATIVE(r_sym);
+                                        r_typ = ELF64_MIPS_R_TYPE(rel->r_info);
+                                        r.r_info = ELF64_R_INFO(r_sym, r_typ);
                                 } else {
                                         r.r_info = TO_NATIVE(rel->r_info);
                                         r_sym = ELF_R_SYM(r.r_info);
@@ -998,6 +1069,14 @@ static void check_sec_ref(struct module *mod, const char *modname,
                                 r_sym = ELF_R_SYM(r.r_info);
 #endif
                                 r.r_addend = 0;
+                                if (hdr->e_machine == EM_386)
+                                        addend_386_rel(elf, i, &r);
+                                else if (hdr->e_machine == EM_ARM)
+                                        addend_arm_rel(elf, i, &r);
+                                else if (hdr->e_machine == EM_MIPS) {
+                                        if (addend_mips_rel(elf, i, &r))
+                                                continue;
+                                }
                                 sym = elf->symtab_start + r_sym;
                                 /* Skip special sections */
                                 if (sym->st_shndx >= SHN_LORESERVE)
diff --git a/scripts/mod/modpost.h b/scripts/mod/modpost.h
index 0858caa9c03f..4156dd34c5de 100644
--- a/scripts/mod/modpost.h
+++ b/scripts/mod/modpost.h
@@ -60,6 +60,9 @@ typedef union
 #define ELF64_MIPS_R_SYM(i) \
   ((__extension__ (_Elf64_Mips_R_Info_union)(i)).r_info_fields.r_sym)
 
+#define ELF64_MIPS_R_TYPE(i) \
+  ((__extension__ (_Elf64_Mips_R_Info_union)(i)).r_info_fields.r_type1)
+
 #if KERNEL_ELFDATA != HOST_ELFDATA
 
 static inline void __endian(const void *src, void *dest, unsigned int size)