[PATCH 2/4] modpost: Check the section flags, not name, to catch missing "ax"/"aw"

Tim Abbott
2009-03-24T05:30:06Z

From: Anders Kaseorg <andersk@mit.edu>

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.

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: Anders Kaseorg <andersk@mit.edu>
---
scripts/mod/modpost.c | 49 ++++++++++++++++++-------------------------------
1 files changed, 18 insertions(+), 31 deletions(-)

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index a7e282e..fba468a 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -713,41 +713,27 @@ 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)
-{
- const char *e = sec + strlen(sec) - 1;
- if (match(sec, section_white_list))
- return 1;
-
- 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"
- "Note that for example <linux/init.h> contains\n"
- "section definitions for use in .S files.\n\n",
- modname, sec);
- }
+static void check_section(const char *modname, struct elf_info *elf,
+ Elf_Shdr *sechdr)
+{
+ const char *sec = sech_name(elf, sechdr);
+
+ 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;
}

@@ -1374,7 +1360,7 @@ 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++) {
@@ -1418,7 +1404,7 @@ 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++) {
@@ -1481,6 +1467,7 @@ 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]);
--
1.6.2