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    SubjectRe: [RFC] Crash on modpost, addend_386_rel()
    On Mon, 21 May 2007 21:52:59 -0700 (PDT), Linus Torvalds <torvalds@linux-foundation.org> wrote:
    > Would you mind also just making this whole logic (that is generic and
    > shared with all the different arch versions) be an inline function of its
    > own?
    >
    > > + Elf_Shdr *sechdrs = elf->sechdrs;
    > > + unsigned int *location;
    > > + int section = sechdrs[rsection].sh_info;
    > > +
    > > + location = (void *)elf->hdr + sechdrs[section].sh_offset +
    > > + (r->r_offset - sechdrs[section].sh_addr);
    >
    > so that all the functions could just use some generic
    >
    > location = reloc_location(elf, rsection, r);
    >
    > or similar, instead of having that complex thing duplicated three times
    > (arm, mips and i386)?

    Sure, updated.

    > Especially since other architectures will likely end up doing the same
    > thing too...

    Archs using RELA instead of REL section are not affected by this
    patch. But I'm not sure how many are using RELA.


    Subject: [PATCH] kbuild: make better section mismatch reports on i386, arm and mips (take 3)

    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.

    Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
    ---
    diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
    index 8e5610d..44c3960 100644
    --- a/scripts/mod/modpost.c
    +++ b/scripts/mod/modpost.c
    @@ -384,6 +384,8 @@ 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);
    + sechdrs[i].sh_addr = TO_NATIVE(sechdrs[i].sh_addr);
    }
    /* Find symbol table. */
    for (i = 1; i < hdr->e_shnum; i++) {
    @@ -753,6 +755,8 @@ 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;
    }
    @@ -895,6 +899,69 @@ static void warn_sec_mismatch(const char *modname, const char *fromsec,
    }
    }

    +static inline unsigned int *reloc_location(struct elf_info *elf,
    + int rsection, Elf_Rela *r)
    +{
    + Elf_Shdr *sechdrs = elf->sechdrs;
    + int section = sechdrs[rsection].sh_info;
    +
    + return (void *)elf->hdr + sechdrs[section].sh_offset +
    + (r->r_offset - sechdrs[section].sh_addr);
    +}
    +
    +static void addend_386_rel(struct elf_info *elf, int rsection, Elf_Rela *r)
    +{
    + unsigned int r_typ = ELF_R_TYPE(r->r_info);
    + unsigned int *location = reloc_location(elf, rsection, r);
    +
    + 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 rsection, Elf_Rela *r)
    +{
    + unsigned int r_typ = ELF_R_TYPE(r->r_info);
    + unsigned int *location = reloc_location(elf, rsection, r);
    +
    + 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 rsection, Elf_Rela *r)
    +{
    + unsigned int r_typ = ELF_R_TYPE(r->r_info);
    + unsigned int *location = reloc_location(elf, rsection, r);
    + unsigned int inst;
    +
    + if (r_typ == R_MIPS_HI16)
    + return 1; /* skip this */
    + inst = TO_NATIVE(*location);
    + switch (r_typ) {
    + case R_MIPS_LO16:
    + r->r_addend = inst & 0xffff;
    + break;
    + case R_MIPS_26:
    + r->r_addend = (inst & 0x03ffffff) << 2;
    + break;
    + case R_MIPS_32:
    + r->r_addend = inst;
    + break;
    + }
    + return 0;
    +}
    +
    /**
    * A module includes a number of sections that are discarded
    * either when loaded or when used as built-in.
    @@ -938,8 +1005,11 @@ 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);
    @@ -972,8 +1042,11 @@ 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);
    @@ -983,6 +1056,14 @@ 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 0858caa..4156dd3 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)
    -
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