Re: [RFC] Crash on modpost, addend_386_rel()

["Mika Penttilä" <mika.penttila@kolumbus.fi>]

Atsushi Nemoto kirjoitti:
> On Tue, 22 May 2007 14:29:29 +0900 (JST), Atsushi Nemoto <nemoto@toshiba-tops.co.jp> wrote:
>   
>> Subject: [PATCH] kbuild: make better section mismatch reports on i386, arm and mips (take 3)
>>     
>
> Updated again to get a little bit better report on i386 relocatable
> vmlinux.
>
>
> Subject: [PATCH] kbuild: make better section mismatch reports on i386, arm and mips (take 4)
>
> 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..760b2b3 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -374,6 +374,7 @@ static int parse_elf(struct elf_info *info, const char *filename)
>  	hdr->e_shstrndx = TO_NATIVE(hdr->e_shstrndx);
>  	hdr->e_shnum    = TO_NATIVE(hdr->e_shnum);
>  	hdr->e_machine  = TO_NATIVE(hdr->e_machine);
> +	hdr->e_type     = TO_NATIVE(hdr->e_type);
>  	sechdrs = (void *)hdr + hdr->e_shoff;
>  	info->sechdrs = sechdrs;
>  
> @@ -384,6 +385,8 @@ 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 +756,8 @@ 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 +900,72 @@ 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;
> +		/* For CONFIG_RELOCATABLE=y */
> +		if (elf->hdr->e_type == ET_EXEC)
> +			r->r_addend += r->r_offset;
> +		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 +1009,11 @@ 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 +1046,11 @@ 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 +1060,14 @@ 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)
> -
>
>   
I can't see how this use of r_attend is going to work. find_elf_symbol
compares relsym->st_value to Elf_Rela->r_attend. I think it doesn't work
for RELA archs and even with this patch for REL.

--Mika