[PATCH 3/4] modpost: Support objects with more than 64k sections

Tim Abbott
2009-03-24T05:30:52Z

From: Denys Vlasenko <vda.linux@googlemail.com>

This patch makes modpost able to process object files with more than
64k sections. Needed for huge kernel builds (allyesconfig, for example)
with -ffunction-sections.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
[andersk@mit.edu: updated for 2.6.29]
Signed-off-by: Anders Kaseorg <andersk@mit.edu>
---
scripts/mod/file2alias.c | 6 +-
scripts/mod/modpost.c | 94 ++++++++++++++++++++++++++++++++-------------
scripts/mod/modpost.h | 43 +++++++++++++++++++++
3 files changed, 113 insertions(+), 30 deletions(-)

diff --git a/scripts/mod/file2alias.c b/scripts/mod/file2alias.c
index 4eea60b..7d3ebb5 100644
--- a/scripts/mod/file2alias.c
+++ b/scripts/mod/file2alias.c
@@ -753,16 +753,16 @@ void handle_moddevtable(struct module *mod, struct elf_info *info,
char *zeros = NULL;

/* We're looking for a section relative symbol */
- if (!sym->st_shndx || sym->st_shndx >= info->hdr->e_shnum)
+ if (!sym->st_shndx || get_secindex(info, sym) >= info->num_sections)
return;

/* Handle all-NULL symbols allocated into .bss */
- if (info->sechdrs[sym->st_shndx].sh_type & SHT_NOBITS) {
+ if (info->sechdrs[get_secindex(info, sym)].sh_type & SHT_NOBITS) {
zeros = calloc(1, sym->st_size);
symval = zeros;
} else {
symval = (void *)info->hdr
- + info->sechdrs[sym->st_shndx].sh_offset
+ + info->sechdrs[get_secindex(info, sym)].sh_offset
+ sym->st_value;
}

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index fba468a..8ee2034 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -244,7 +244,7 @@ static enum export export_no(const char *s)
return export_unknown;
}

-static enum export export_from_sec(struct elf_info *elf, Elf_Section sec)
+static enum export export_from_sec(struct elf_info *elf, unsigned int sec)
{
if (sec == elf->export_sec)
return export_plain;
@@ -364,6 +364,8 @@ static int parse_elf(struct elf_info *info, const char *filename)
Elf_Ehdr *hdr;
Elf_Shdr *sechdrs;
Elf_Sym *sym;
+ const char *secstrings;
+ unsigned int symtab_idx = ~0U, symtab_shndx_idx = ~0U;

hdr = grab_file(filename, &info->size);
if (!hdr) {
@@ -400,8 +402,19 @@ static int parse_elf(struct elf_info *info, const char *filename)
return 0;
}

+ /* Fixups for more than 64k sections */
+ info->num_sections = hdr->e_shnum;
+ if (info->num_sections == 0) { /* more than 64k sections? */
+ /* doesn't need shndx2secindex() */
+ info->num_sections = TO_NATIVE(sechdrs[0].sh_size);
+ }
+ info->secindex_strings = hdr->e_shstrndx;
+ if (info->secindex_strings == SHN_XINDEX)
+ info->secindex_strings =
+ shndx2secindex(TO_NATIVE(sechdrs[0].sh_link));
+
/* Fix endianness in section headers */
- for (i = 0; i < hdr->e_shnum; i++) {
+ for (i = 0; i < info->num_sections; i++) {
sechdrs[i].sh_type = TO_NATIVE(sechdrs[i].sh_type);
sechdrs[i].sh_offset = TO_NATIVE(sechdrs[i].sh_offset);
sechdrs[i].sh_size = TO_NATIVE(sechdrs[i].sh_size);
@@ -411,9 +424,8 @@ static int parse_elf(struct elf_info *info, const char *filename)
sechdrs[i].sh_addr = TO_NATIVE(sechdrs[i].sh_addr);
}
/* Find symbol table. */
- for (i = 1; i < hdr->e_shnum; i++) {
- const char *secstrings
- = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
+ secstrings = (void *)hdr + sechdrs[info->secindex_strings].sh_offset;
+ for (i = 1; i < info->num_sections; i++) {
const char *secname;

if (sechdrs[i].sh_offset > info->size) {
@@ -440,14 +452,24 @@ static int parse_elf(struct elf_info *info, const char *filename)
else if (strcmp(secname, "__markers_strings") == 0)
info->markers_strings_sec = i;

- if (sechdrs[i].sh_type != SHT_SYMTAB)
- continue;
+ if (sechdrs[i].sh_type == SHT_SYMTAB) {
+ symtab_idx = i;
+ info->symtab_start = (void *)hdr +
+ sechdrs[i].sh_offset;
+ info->symtab_stop = (void *)hdr +
+ sechdrs[i].sh_offset + sechdrs[i].sh_size;
+ info->strtab = (void *)hdr +
+ sechdrs[shndx2secindex(sechdrs[i].sh_link)].sh_offset;
+ }

- info->symtab_start = (void *)hdr + sechdrs[i].sh_offset;
- info->symtab_stop = (void *)hdr + sechdrs[i].sh_offset
- + sechdrs[i].sh_size;
- info->strtab = (void *)hdr +
- sechdrs[sechdrs[i].sh_link].sh_offset;
+ /* 32bit section no. table? ("more than 64k sections") */
+ if (sechdrs[i].sh_type == SHT_SYMTAB_SHNDX) {
+ symtab_shndx_idx = i;
+ info->symtab_shndx_start = (void *)hdr +
+ sechdrs[i].sh_offset;
+ info->symtab_shndx_stop = (void *)hdr +
+ sechdrs[i].sh_offset + sechdrs[i].sh_size;
+ }
}
if (!info->symtab_start)
fatal("%s has no symtab?\n", filename);
@@ -459,6 +481,21 @@ static int parse_elf(struct elf_info *info, const char *filename)
sym->st_value = TO_NATIVE(sym->st_value);
sym->st_size = TO_NATIVE(sym->st_size);
}
+
+ if (symtab_shndx_idx != ~0U) {
+ Elf32_Word *p;
+ if (symtab_idx !=
+ shndx2secindex(sechdrs[symtab_shndx_idx].sh_link))
+ fatal("%s: SYMTAB_SHNDX has bad sh_link: %u!=%u\n",
+ filename,
+ shndx2secindex(sechdrs[symtab_shndx_idx].sh_link),
+ symtab_idx);
+ /* Fix endianness */
+ for (p = info->symtab_shndx_start; p < info->symtab_shndx_stop;
+ p++)
+ *p = TO_NATIVE(*p);
+ }
+
return 1;
}

@@ -493,7 +530,7 @@ static void handle_modversions(struct module *mod, struct elf_info *info,
Elf_Sym *sym, const char *symname)
{
unsigned int crc;
- enum export export = export_from_sec(info, sym->st_shndx);
+ enum export export = export_from_sec(info, get_secindex(info, sym));

switch (sym->st_shndx) {
case SHN_COMMON:
@@ -635,18 +672,18 @@ static const char *sym_name(struct elf_info *elf, Elf_Sym *sym)
return "(unknown)";
}

-static const char *sec_name(struct elf_info *elf, int shndx)
+static const char *sec_name(struct elf_info *elf, int secindex)
{
Elf_Shdr *sechdrs = elf->sechdrs;
return (void *)elf->hdr +
- elf->sechdrs[elf->hdr->e_shstrndx].sh_offset +
- sechdrs[shndx].sh_name;
+ elf->sechdrs[elf->secindex_strings].sh_offset +
+ sechdrs[secindex].sh_name;
}

static const char *sech_name(struct elf_info *elf, Elf_Shdr *sechdr)
{
return (void *)elf->hdr +
- elf->sechdrs[elf->hdr->e_shstrndx].sh_offset +
+ elf->sechdrs[elf->secindex_strings].sh_offset +
sechdr->sh_name;
}

@@ -983,11 +1020,14 @@ static Elf_Sym *find_elf_symbol(struct elf_info *elf, Elf64_Sword addr,
Elf_Sym *near = NULL;
Elf64_Sword distance = 20;
Elf64_Sword d;
+ unsigned int relsym_secindex;

if (relsym->st_name != 0)
return relsym;
+
+ relsym_secindex = get_secindex(elf, relsym);
for (sym = elf->symtab_start; sym < elf->symtab_stop; sym++) {
- if (sym->st_shndx != relsym->st_shndx)
+ if (get_secindex(elf, sym) != relsym_secindex)
continue;
if (ELF_ST_TYPE(sym->st_info) == STT_SECTION)
continue;
@@ -1049,9 +1089,9 @@ static Elf_Sym *find_elf_symbol2(struct elf_info *elf, Elf_Addr addr,
for (sym = elf->symtab_start; sym < elf->symtab_stop; sym++) {
const char *symsec;

- if (sym->st_shndx >= SHN_LORESERVE)
+ if (is_shndx_special(sym->st_shndx))
continue;
- symsec = sec_name(elf, sym->st_shndx);
+ symsec = sec_name(elf, get_secindex(elf, sym));
if (strcmp(symsec, sec) != 0)
continue;
if (!is_valid_name(elf, sym))
@@ -1248,7 +1288,7 @@ static void check_section_mismatch(const char *modname, struct elf_info *elf,
const char *tosec;
enum mismatch mismatch;

- tosec = sec_name(elf, sym->st_shndx);
+ tosec = sec_name(elf, get_secindex(elf, sym));
mismatch = section_mismatch(fromsec, tosec);
if (mismatch != NO_MISMATCH) {
Elf_Sym *to;
@@ -1275,7 +1315,7 @@ static unsigned int *reloc_location(struct elf_info *elf,
Elf_Shdr *sechdr, Elf_Rela *r)
{
Elf_Shdr *sechdrs = elf->sechdrs;
- int section = sechdr->sh_info;
+ int section = shndx2secindex(sechdr->sh_info);

return (void *)elf->hdr + sechdrs[section].sh_offset +
(r->r_offset - sechdrs[section].sh_addr);
@@ -1383,7 +1423,7 @@ static void section_rela(const char *modname, struct elf_info *elf,
r.r_addend = TO_NATIVE(rela->r_addend);
sym = elf->symtab_start + r_sym;
/* Skip special sections */
- if (sym->st_shndx >= SHN_LORESERVE)
+ if (is_shndx_special(sym->st_shndx))
continue;
check_section_mismatch(modname, elf, &r, sym, fromsec);
}
@@ -1441,7 +1481,7 @@ static void section_rel(const char *modname, struct elf_info *elf,
}
sym = elf->symtab_start + r_sym;
/* Skip special sections */
- if (sym->st_shndx >= SHN_LORESERVE)
+ if (is_shndx_special(sym->st_shndx))
continue;
check_section_mismatch(modname, elf, &r, sym, fromsec);
}
@@ -1466,7 +1506,7 @@ static void check_sec_ref(struct module *mod, const char *modname,
Elf_Shdr *sechdrs = elf->sechdrs;

/* Walk through all sections */
- for (i = 0; i < elf->hdr->e_shnum; i++) {
+ for (i = 0; i < elf->num_sections; 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)
@@ -1496,7 +1536,7 @@ static void get_markers(struct elf_info *info, struct module *mod)
n = 0;
for (sym = info->symtab_start; sym < info->symtab_stop; sym++)
if (ELF_ST_TYPE(sym->st_info) == STT_OBJECT &&
- sym->st_shndx == info->markers_strings_sec &&
+ get_secindex(info, sym) == info->markers_strings_sec &&
!strncmp(info->strtab + sym->st_name,
"__mstrtab_", sizeof "__mstrtab_" - 1)) {
if (first_sym == NULL)
@@ -1520,7 +1560,7 @@ static void get_markers(struct elf_info *info, struct module *mod)
n = 0;
for (sym = first_sym; sym <= last_sym; sym++)
if (ELF_ST_TYPE(sym->st_info) == STT_OBJECT &&
- sym->st_shndx == info->markers_strings_sec &&
+ get_secindex(info, sym) == info->markers_strings_sec &&
!strncmp(info->strtab + sym->st_name,
"__mstrtab_", sizeof "__mstrtab_" - 1)) {
const char *name = strings + sym->st_value;
diff --git a/scripts/mod/modpost.h b/scripts/mod/modpost.h
index 09f58e3..dbde650 100644
--- a/scripts/mod/modpost.h
+++ b/scripts/mod/modpost.h
@@ -132,8 +132,51 @@ struct elf_info {
const char *strtab;
char *modinfo;
unsigned int modinfo_len;
+
+ /* support for 32bit section numbers */
+
+ unsigned int num_sections; /* max_secindex + 1 */
+ unsigned int secindex_strings;
+ /* if Nth symbol table entry has .st_shndx = SHN_XINDEX,
+ * take shndx from symtab_shndx_start[N] instead */
+ Elf32_Word *symtab_shndx_start;
+ Elf32_Word *symtab_shndx_stop;
};

+static inline int is_shndx_special(unsigned int i)
+{
+ return i != SHN_XINDEX && i >= SHN_LORESERVE && i <= SHN_HIRESERVE;
+}
+
+/* shndx is in [0..SHN_LORESERVE) U (SHN_HIRESERVE, 0xfffffff], thus:
+ * shndx == 0 <=> sechdrs[0]
+ * ......
+ * shndx == SHN_LORESERVE-1 <=> sechdrs[SHN_LORESERVE-1]
+ * shndx == SHN_HIRESERVE+1 <=> sechdrs[SHN_LORESERVE]
+ * shndx == SHN_HIRESERVE+2 <=> sechdrs[SHN_LORESERVE+1]
+ * ......
+ * fyi: sym->st_shndx is uint16, SHN_LORESERVE = ff00, SHN_HIRESERVE = ffff,
+ * so basically we map 0000..feff -> 0000..feff
+ * ff00..ffff -> (you are a bad boy, dont do it)
+ * 10000..xxxx -> ff00..(xxxx-0x100)
+ */
+static inline unsigned int shndx2secindex(unsigned int i)
+{
+ if (i <= SHN_HIRESERVE)
+ return i;
+ return i - (SHN_HIRESERVE + 1 - SHN_LORESERVE);
+}
+
+/* Accessor for sym->st_shndx, hides ugliness of "64k sections" */
+static inline unsigned int get_secindex(const struct elf_info *info,
+ const Elf_Sym *sym)
+{
+ if (sym->st_shndx != SHN_XINDEX)
+ return sym->st_shndx;
+ return shndx2secindex(info->symtab_shndx_start[sym -
+ info->symtab_start]);
+}
+
/* file2alias.c */
extern unsigned int cross_build;
void handle_moddevtable(struct module *mod, struct elf_info *info,
--
1.6.2