Commit b614a697 authored by Anders Kaseorg's avatar Anders Kaseorg Committed by Sam Ravnborg
Browse files

kbuild, modpost: Check the section flags, to catch missing "ax"/"aw" 



When you put
  .section ".foo"
in an assembly file instead of
  .section "foo", "ax"
, one of the possible symptoms is that modpost will see an
ld-generated section name ".foo.1" in section_rel() or section_rela().
But this heuristic has two problems: it will miss a bad section that
has no relocations, and it will incorrectly flag many gcc-generated
sections as bad when compiling with -ffunction-sections
-fdata-sections.

On mips it fixes a lot of bogus warnings with gcc 4.4.0 lije this one:
WARNING: crypto/cryptd.o (.text.T.349): unexpected section name.

So instead of checking whether the section name matches a particular
pattern, we directly check for a missing SHF_ALLOC in the section
flags.

Signed-off-by: default avatarAnders Kaseorg <andersk@mit.edu>
Tested-by: default avatarRalf Baechle <ralf@linux-mips.org>
Signed-off-by: default avatarSam Ravnborg <sam@ravnborg.org>
parent c993971f

scripts/mod/modpost.c

+19 −32
Original line number Diff line number Diff line
@@ -716,42 +716,28 @@ int match(const char *sym, const char * const pat[]) 


/* sections that we do not want to do full section mismatch check on */

static const char *section_white_list[] =

	{ ".debug*", ".stab*", ".note*", ".got*", ".toc*", NULL };

	{ ".comment", ".debug*", ".stab*", ".note*", ".got*", ".toc*", NULL };



/*

 * Is this section one we do not want to check?

 * This is often debug sections.

 * If we are going to check this section then

 * test if section name ends with a dot and a number.

 * This is used to find sections where the linker have

 * appended a dot-number to make the name unique.

 * This is used to find sections missing the SHF_ALLOC flag.

 * The cause of this is often a section specified in assembler

 * without "ax" / "aw" and the same section used in .c

 * code where gcc add these.

 * without "ax" / "aw".

 */

static int check_section(const char *modname, const char *sec)

static void check_section(const char *modname, struct elf_info *elf,

                          Elf_Shdr *sechdr)

{

	const char *e = sec + strlen(sec) - 1;

	if (match(sec, section_white_list))

		return 1;

	const char *sec = sech_name(elf, sechdr);



	if (*e && isdigit(*e)) {

		/* consume all digits */

		while (*e && e != sec && isdigit(*e))

			e--;

		if (*e == '.' && !strstr(sec, ".linkonce")) {

			warn("%s (%s): unexpected section name.\n"

			     "The (.[number]+) following section name are "

			     "ld generated and not expected.\n"

			     "Did you forget to use \"ax\"/\"aw\" "

			     "in a .S file?\n"

	if (sechdr->sh_type == SHT_PROGBITS &&

	    !(sechdr->sh_flags & SHF_ALLOC) &&

	    !match(sec, section_white_list)) {

		warn("%s (%s): unexpected non-allocatable section.\n"

		     "Did you forget to use \"ax\"/\"aw\" in a .S file?\n"

		     "Note that for example <linux/init.h> contains\n"

		     "section definitions for use in .S files.\n\n",

		     modname, sec);

	}

}

	return 0;

}
@@ -1358,7 +1344,7 @@ static void section_rela(const char *modname, struct elf_info *elf, 
	fromsec = sech_name(elf, sechdr);

	fromsec += strlen(".rela");

	/* if from section (name) is know good then skip it */

	if (check_section(modname, fromsec))

	if (match(fromsec, section_white_list))

		return;



	for (rela = start; rela < stop; rela++) {
@@ -1402,7 +1388,7 @@ static void section_rel(const char *modname, struct elf_info *elf, 
	fromsec = sech_name(elf, sechdr);

	fromsec += strlen(".rel");

	/* if from section (name) is know good then skip it */

	if (check_section(modname, fromsec))

	if (match(fromsec, section_white_list))

		return;



	for (rel = start; rel < stop; rel++) {
@@ -1465,6 +1451,7 @@ static void check_sec_ref(struct module *mod, const char *modname, 


	/* Walk through all sections */

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

		check_section(modname, elf, &elf->sechdrs[i]);

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

		if (sechdrs[i].sh_type == SHT_RELA)

			section_rela(modname, elf, &elf->sechdrs[i]);

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