Commit b39927cf authored by Sam Ravnborg's avatar Sam Ravnborg
Browse files

kbuild: check for section mismatch during modpost stage 



Section mismatch is identified as references to .init*
sections from non .init sections. And likewise references
to .exit.* sections outside .exit sections.

.init.* sections are discarded after a module is initialized
and references to .init.* sections are oops candidates.
.exit.* sections are discarded when a module is built-in and
thus references to .exit are also oops candidates.

The checks were possible to do using 'make buildcheck' which
called the two perl scripts: reference_discarded.pl and
reference_init.pl. This patch just moves the same functionality
inside modpost and the scripts are then obsoleted.
They will though be kept for a while so users can do double
checks - but note that some .o files are skipped by the perl scripts
so result is not 1:1.
All credit for the concept goes to Keith Owens who implemented
the original perl scrips - this patch just moves it to modpost.

Compared to the perl script the implmentation in modpost will be run
for each kernel build - thus catching the error much sooner, but
the downside is that the individual .o file are not always identified.

Signed-off-by: default avatarSam Ravnborg <sam@ravnborg.org>
parent a67dc21a

scripts/mod/modpost.c

+258 −0
Original line number Diff line number Diff line
@@ -451,6 +451,262 @@ static char *get_modinfo(void *modinfo, unsigned long modinfo_len, 
	return NULL;

}



/*

 * Find symbols before or equal addr and after addr - in the section sec

 **/

static void find_symbols_between(struct elf_info *elf, Elf_Addr addr,

				 const char *sec,

			         Elf_Sym **before, Elf_Sym **after)

{

	Elf_Sym *sym;

	Elf_Ehdr *hdr = elf->hdr;

	Elf_Addr beforediff = ~0;

	Elf_Addr afterdiff = ~0;

	const char *secstrings = (void *)hdr +

				 elf->sechdrs[hdr->e_shstrndx].sh_offset;

	

	*before = NULL;

	*after = NULL;



	for (sym = elf->symtab_start; sym < elf->symtab_stop; sym++) {

		const char *symsec;



		if (sym->st_shndx >= SHN_LORESERVE)

			continue;

		symsec = secstrings + elf->sechdrs[sym->st_shndx].sh_name;

		if (strcmp(symsec, sec) != 0)

			continue;

		if (sym->st_value <= addr) {

			if ((addr - sym->st_value) < beforediff) {

				beforediff = addr - sym->st_value;

				*before = sym;

			}

		}

		else

		{

			if ((sym->st_value - addr) < afterdiff) {

				afterdiff = sym->st_value - addr;

				*after = sym;

			}

		}

	}

}



/**

 * Print a warning about a section mismatch.

 * Try to find symbols near it so user can find it.

 **/

static void warn_sec_mismatch(const char *modname, const char *fromsec,

			      struct elf_info *elf, Elf_Sym *sym, Elf_Rela r)

{

	Elf_Sym *before;

	Elf_Sym *after;

	Elf_Ehdr *hdr = elf->hdr;

	Elf_Shdr *sechdrs = elf->sechdrs;

	const char *secstrings = (void *)hdr +

				 sechdrs[hdr->e_shstrndx].sh_offset;

	const char *secname = secstrings + sechdrs[sym->st_shndx].sh_name;

	

	find_symbols_between(elf, r.r_offset, fromsec, &before, &after);



	if (before && after) {

		warn("%s - Section mismatch: reference to %s from %s "

		     "between '%s' (at offset 0x%lx) and '%s'\n",

		     modname, secname, fromsec,

		     elf->strtab + before->st_name,

		     (long)(r.r_offset - before->st_value),

		     elf->strtab + after->st_name);

	} else if (before) {

		warn("%s - Section mismatch: reference to %s from %s "

		     "after '%s' (at offset 0x%lx)\n",

		     modname, secname, fromsec, 

		     elf->strtab + before->st_name,

		     (long)(r.r_offset - before->st_value));

	} else if (after) {

		warn("%s - Section mismatch: reference to %s from %s "

		     "before '%s' (at offset -0x%lx)\n",

		     modname, secname, fromsec, 

		     elf->strtab + before->st_name,

		     (long)(before->st_value - r.r_offset));

	} else {

		warn("%s - Section mismatch: reference to %s from %s "

		     "(offset 0x%lx)\n",

		     modname, secname, fromsec, (long)r.r_offset);

	}

}



/**

 * A module includes a number of sections that are discarded

 * either when loaded or when used as built-in.

 * For loaded modules all functions marked __init and all data

 * marked __initdata will be discarded when the module has been intialized.

 * Likewise for modules used built-in the sections marked __exit

 * are discarded because __exit marked function are supposed to be called

 * only when a moduel is unloaded which never happes for built-in modules.

 * The check_sec_ref() function traverses all relocation records

 * to find all references to a section that reference a section that will

 * be discarded and warns about it.

 **/

static void check_sec_ref(struct module *mod, const char *modname,

			  struct elf_info *elf,

			  int section(const char*),

			  int section_ref_ok(const char *))

{

	int i;

	Elf_Sym  *sym;

	Elf_Ehdr *hdr = elf->hdr;

	Elf_Shdr *sechdrs = elf->sechdrs;

	const char *secstrings = (void *)hdr +

				 sechdrs[hdr->e_shstrndx].sh_offset;

		

	/* Walk through all sections */

	for (i = 0; i < hdr->e_shnum; i++) {

		const char *name = secstrings + sechdrs[i].sh_name +

						strlen(".rela");

		/* We want to process only relocation sections and not .init */

		if (section_ref_ok(name) || (sechdrs[i].sh_type != SHT_RELA))

			continue;

		Elf_Rela *rela;

		Elf_Rela *start = (void *)hdr + sechdrs[i].sh_offset;

		Elf_Rela *stop  = (void*)start + sechdrs[i].sh_size;



		for (rela = start; rela < stop; rela++) {

			Elf_Rela r;

			const char *secname;

			r.r_offset = TO_NATIVE(rela->r_offset);

			r.r_info   = TO_NATIVE(rela->r_info);

			sym = elf->symtab_start + ELF_R_SYM(r.r_info);

			secname = secstrings + sechdrs[sym->st_shndx].sh_name;

			/* Skip special sections */

			if (sym->st_shndx >= SHN_LORESERVE)

				continue;



			if (section(secname))

				warn_sec_mismatch(modname, name, elf, sym, r);

		}

	}

}



/**

 * Functions used only during module init is marked __init and is stored in

 * a .init.text section. Likewise data is marked __initdata and stored in

 * a .init.data section.

 * If this section is one of these sections return 1

 * See include/linux/init.h for the details

 **/

static int init_section(const char *name)

{

	if (strcmp(name, ".init") == 0)

		return 1;

	if (strncmp(name, ".init.", strlen(".init.")) == 0)

		return 1;

	return 0;

}



/**

 * Identify sections from which references to a .init section is OK.

 * 

 * Unfortunately references to read only data that referenced .init

 * sections had to be excluded. Almost all of these are false

 * positives, they are created by gcc. The downside of excluding rodata

 * is that there really are some user references from rodata to

 * init code, e.g. drivers/video/vgacon.c:

 * 

 * const struct consw vga_con = {

 *        con_startup:            vgacon_startup,

 *

 * where vgacon_startup is __init.  If you want to wade through the false

 * positives, take out the check for rodata.

 **/

static int init_section_ref_ok(const char *name)

{

	const char **s;

	/* Absolute section names */

	const char *namelist1[] = {

		".init",

		".stab",

		".rodata",

		".text.lock",

		".pci_fixup_header",

		".pci_fixup_final",

		".pdr",

		"__param",

		NULL

	};

	/* Start of section names */

	const char *namelist2[] = {

		".init.",

		".altinstructions",

		".eh_frame",

		".debug",

		NULL

	};

	

	for (s = namelist1; *s; s++)

		if (strcmp(*s, name) == 0)

			return 1;

	for (s = namelist2; *s; s++)	

		if (strncmp(*s, name, strlen(*s)) == 0)

			return 1;

	return 0;

}



/*

 * Functions used only during module exit is marked __exit and is stored in

 * a .exit.text section. Likewise data is marked __exitdata and stored in

 * a .exit.data section.

 * If this section is one of these sections return 1

 * See include/linux/init.h for the details

 **/

static int exit_section(const char *name)

{

	if (strcmp(name, ".exit.text") == 0)

		return 1;

	if (strcmp(name, ".exit.data") == 0)

		return 1;

	return 0;

	

}



/*

 * Identify sections from which references to a .exit section is OK.

 * 

 * [OPD] Keith Ownes <kaos@sgi.com> commented:

 * For our future {in}sanity, add a comment that this is the ppc .opd

 * section, not the ia64 .opd section.

 * ia64 .opd should not point to discarded sections.

 **/

static int exit_section_ref_ok(const char *name)

{

	const char **s;

	/* Absolute section names */

	const char *namelist1[] = {

		".exit.text",

		".exit.data",

		".init.text",

		".opd", /* See comment [OPD] */

		".altinstructions",

		".pdr",

		".exitcall.exit",

		".eh_frame",

		".stab",

		NULL

	};

	/* Start of section names */

	const char *namelist2[] = {

		".debug",

		NULL

	};

	

	for (s = namelist1; *s; s++)

		if (strcmp(*s, name) == 0)

			return 1;

	for (s = namelist2; *s; s++)	

		if (strncmp(*s, name, strlen(*s)) == 0)

			return 1;

	return 0;

}



static void read_symbols(char *modname)

{

	const char *symname;
@@ -476,6 +732,8 @@ static void read_symbols(char *modname) 
		handle_modversions(mod, &info, sym, symname);

		handle_moddevtable(mod, &info, sym, symname);

	}

	check_sec_ref(mod, modname, &info, init_section, init_section_ref_ok);

	check_sec_ref(mod, modname, &info, exit_section, exit_section_ref_ok);



	version = get_modinfo(info.modinfo, info.modinfo_len, "version");

	if (version)

scripts/mod/modpost.h

+10 −0
Original line number Diff line number Diff line
@@ -16,17 +16,27 @@ 
#define Elf_Ehdr    Elf32_Ehdr 

#define Elf_Shdr    Elf32_Shdr 

#define Elf_Sym     Elf32_Sym

#define Elf_Addr    Elf32_Addr

#define Elf_Section Elf32_Section

#define ELF_ST_BIND ELF32_ST_BIND

#define ELF_ST_TYPE ELF32_ST_TYPE



#define Elf_Rela    Elf32_Rela

#define ELF_R_SYM   ELF32_R_SYM

#define ELF_R_TYPE  ELF32_R_TYPE

#else



#define Elf_Ehdr    Elf64_Ehdr 

#define Elf_Shdr    Elf64_Shdr 

#define Elf_Sym     Elf64_Sym

#define Elf_Addr    Elf64_Addr

#define Elf_Section Elf64_Section

#define ELF_ST_BIND ELF64_ST_BIND

#define ELF_ST_TYPE ELF64_ST_TYPE



#define Elf_Rela    Elf64_Rela

#define ELF_R_SYM   ELF64_R_SYM

#define ELF_R_TYPE  ELF64_R_TYPE

#endif



#if KERNEL_ELFDATA != HOST_ELFDATA

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