modpost: support objects with more than 64k sections

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. 64k sections handling is covered, for example,
by this document:

"IA-64 gABI Proposal 74: Section Indexes"
http://www.codesourcery.com/public/cxx-abi/abi/prop-74-sindex.html

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Signed-off-by: Anders Kaseorg <andersk@mit.edu>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>

3 files changed, 122 insertions, 29 deletions

diff --git a/scripts/mod/file2alias.c b/scripts/mod/file2alias.c
index 220213e603db..33f436328f9a 100644
--- a/scripts/mod/file2alias.c
+++ b/scripts/mod/file2alias.c
@@ -839,16 +839,16 @@ 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 3318692e4e76..7249ab44f44c 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -253,7 +253,7 @@ 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;
@@ -373,6 +373,8 @@ 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) {
@@ -417,8 +419,27 @@ static int parse_elf(struct elf_info *info, const char *filename)
                 return 0;
         }
 
+        if (hdr->e_shnum == 0) {
+                /*
+                 * There are more than 64k sections,
+                 * read count from .sh_size.
+                 * note: it doesn't need shndx2secindex()
+                 */
+                info->num_sections = TO_NATIVE(sechdrs[0].sh_size);
+        }
+        else {
+                info->num_sections = hdr->e_shnum;
+        }
+        if (hdr->e_shstrndx == SHN_XINDEX) {
+                info->secindex_strings =
+                    shndx2secindex(TO_NATIVE(sechdrs[0].sh_link));
+        }
+        else {
+                info->secindex_strings = hdr->e_shstrndx;
+        }
+
         /* Fix endianness in section headers */
-        for (i = 0; i < hdr->e_shnum; i++) {
+        for (i = 0; i < info->num_sections; i++) {
                 sechdrs[i].sh_name      = TO_NATIVE(sechdrs[i].sh_name);
                 sechdrs[i].sh_type      = TO_NATIVE(sechdrs[i].sh_type);
                 sechdrs[i].sh_flags     = TO_NATIVE(sechdrs[i].sh_flags);
@@ -431,9 +452,8 @@ static int parse_elf(struct elf_info *info, const char *filename)
                 sechdrs[i].sh_entsize   = TO_NATIVE(sechdrs[i].sh_entsize);
         }
         /* 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;
                 int nobits = sechdrs[i].sh_type == SHT_NOBITS;
 
@@ -461,14 +481,26 @@ static int parse_elf(struct elf_info *info, const char *filename)
                 else if (strcmp(secname, "__ksymtab_gpl_future") == 0)
                         info->export_gpl_future_sec = i;
 
-                if (sechdrs[i].sh_type != SHT_SYMTAB)
-                        continue;
+                if (sechdrs[i].sh_type == SHT_SYMTAB) {
+                        unsigned int sh_link_idx;
+                        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;
+                        sh_link_idx = shndx2secindex(sechdrs[i].sh_link);
+                        info->strtab       = (void *)hdr +
+                            sechdrs[sh_link_idx].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);
@@ -480,6 +512,21 @@ 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;
 }
 
@@ -514,7 +561,7 @@ 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:
@@ -656,19 +703,19 @@ 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 +
-                sechdr->sh_name;
+                elf->sechdrs[elf->secindex_strings].sh_offset +
+                sechdr->sh_name;
 }
 
 /* if sym is empty or point to a string
@@ -1047,11 +1094,14 @@ 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;
@@ -1113,9 +1163,9 @@ 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))
@@ -1311,7 +1361,7 @@ static void check_section_mismatch(const char *modname, struct elf_info *elf,
         const char *tosec;
         const struct sectioncheck *mismatch;
 
-        tosec = sec_name(elf, sym->st_shndx);
+        tosec = sec_name(elf, get_secindex(elf, sym));
         mismatch = section_mismatch(fromsec, tosec);
         if (mismatch) {
                 Elf_Sym *to;
@@ -1339,7 +1389,7 @@ 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);
@@ -1447,7 +1497,7 @@ 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);
         }
@@ -1505,7 +1555,7 @@ 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);
         }
@@ -1530,7 +1580,7 @@ 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)
diff --git a/scripts/mod/modpost.h b/scripts/mod/modpost.h
index be987a44f250..0388cfccac8d 100644
--- a/scripts/mod/modpost.h
+++ b/scripts/mod/modpost.h
@@ -129,8 +129,51 @@ 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,