[PATCH 3/4] build system: section garbage collection for vmlinux

From: Denys Vlasenko
Date: Tue Sep 11 2007 - 16:19:52 EST

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

This patch basically fixes modpost, it isn't specific
for section garbage collection.

Please apply.

Signed-off-by: Denys Vlasenko <vda.linux@xxxxxxxxxxxxxx>
--
vda
--- linux-2.6.23-rc4.gc2/scripts/mod/file2alias.c Sun Sep 2 17:29:37 2007
+++ linux-2.6.23-rc4.gc3/scripts/mod/file2alias.c Sat Sep 8 22:07:54 2007
@@ -529,11 +529,11 @@
void *symval;

/* 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;

symval = (void *)info->hdr
- + info->sechdrs[sym->st_shndx].sh_offset
+ + info->sechdrs[get_secindex(info, sym)].sh_offset
+ sym->st_value;

if (sym_is(symname, "__mod_pci_device_table"))
--- linux-2.6.23-rc4.gc2/scripts/mod/modpost.c Sat Sep 8 22:06:52 2007
+++ linux-2.6.23-rc4.gc3/scripts/mod/modpost.c Sat Sep 8 22:07:54 2007
@@ -235,7 +235,7 @@
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 sec)
{
if (sec == elf->export_sec)
return export_plain;
@@ -353,6 +353,8 @@
Elf_Ehdr *hdr;
Elf_Shdr *sechdrs;
Elf_Sym *sym;
+ const char *secstrings;
+ unsigned int symtab_idx = ~0U;

hdr = grab_file(filename, &info->size);
if (!hdr) {
@@ -372,6 +374,7 @@
/* Not an ELF file - silently ignore it */
return 0;
}
+
/* Fix endianness in ELF header */
hdr->e_shoff = TO_NATIVE(hdr->e_shoff);
hdr->e_shstrndx = TO_NATIVE(hdr->e_shstrndx);
@@ -381,8 +384,18 @@
sechdrs = (void *)hdr + hdr->e_shoff;
info->sechdrs = sechdrs;

+ /* Fixups for more than 64k sections */
+ info->num_sections = hdr->e_shnum;
+ if (info->num_sections == SHN_UNDEF) { /* 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);
@@ -392,9 +405,8 @@
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) {
@@ -416,14 +428,29 @@
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) {
+ 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) {
+ uint32_t *p32;
+ info->symtab_shndx = (void *)hdr + sechdrs[i].sh_offset;
+ if (symtab_idx != shndx2secindex(sechdrs[i].sh_link))
+ fatal("%s: SYMTAB_SHNDX has bad sh_link: %u!=%u\n",
+ filename,
+ shndx2secindex(sechdrs[i].sh_link),
+ symtab_idx);
+ /* Fix endianness */
+ p32 = (void*)info->symtab_shndx + sechdrs[i].sh_size;
+ while (--p32 >= info->symtab_shndx)
+ *p32 = TO_NATIVE(*p32);
+ }
}
if (!info->symtab_start) {
fatal("%s has no symtab?\n", filename);
@@ -450,7 +477,7 @@
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:
@@ -758,11 +785,14 @@
Elf_Sym *relsym)
{
Elf_Sym *sym;
+ unsigned 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;
@@ -811,7 +841,7 @@
Elf_Addr beforediff = ~0;
Elf_Addr afterdiff = ~0;
const char *secstrings = (void *)hdr +
- elf->sechdrs[hdr->e_shstrndx].sh_offset;
+ elf->sechdrs[elf->secindex_strings].sh_offset;

*before = NULL;
*after = NULL;
@@ -819,9 +849,9 @@
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 = secstrings + elf->sechdrs[sym->st_shndx].sh_name;
+ symsec = secstrings + elf->sechdrs[get_secindex(elf, sym)].sh_name;
if (strcmp(symsec, sec) != 0)
continue;
if (!is_valid_name(elf, sym))
@@ -862,8 +892,8 @@
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;
+ sechdrs[elf->secindex_strings].sh_offset;
+ const char *secname = secstrings + sechdrs[get_secindex(elf, sym)].sh_name;

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

@@ -997,10 +1027,10 @@
Elf_Ehdr *hdr = elf->hdr;
Elf_Shdr *sechdrs = elf->sechdrs;
const char *secstrings = (void *)hdr +
- sechdrs[hdr->e_shstrndx].sh_offset;
+ sechdrs[elf->secindex_strings].sh_offset;

/* Walk through all sections */
- for (i = 0; i < hdr->e_shnum; i++) {
+ for (i = 0; i < elf->num_sections; i++) {
const char *name = secstrings + sechdrs[i].sh_name;
const char *secname;
Elf_Rela r;
@@ -1034,11 +1064,11 @@
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;

secname = secstrings +
- sechdrs[sym->st_shndx].sh_name;
+ sechdrs[get_secindex(elf, sym)].sh_name;
if (section(secname))
warn_sec_mismatch(modname, name,
elf, sym, r);
@@ -1085,11 +1115,11 @@
}
sym = elf->symtab_start + r_sym;
/* Skip special sections */
- if (sym->st_shndx >= SHN_LORESERVE)
+ if (is_shndx_special(sym->st_shndx))
continue;

secname = secstrings +
- sechdrs[sym->st_shndx].sh_name;
+ sechdrs[get_secindex(elf, sym)].sh_name;
if (section(secname))
warn_sec_mismatch(modname, name,
elf, sym, r);
--- linux-2.6.23-rc4.gc2/scripts/mod/modpost.h Sun Sep 2 17:29:37 2007
+++ linux-2.6.23-rc4.gc3/scripts/mod/modpost.h Sat Sep 8 22:07:54 2007
@@ -127,7 +127,48 @@
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[N] instead */
+ uint32_t *symtab_shndx;
};
+
+static inline int is_shndx_special(unsigned 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 shndx2secindex(unsigned 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 get_secindex(struct elf_info *info, Elf_Sym *sym)
+{
+ if (sym->st_shndx != SHN_XINDEX)
+ return sym->st_shndx;
+ return shndx2secindex(info->symtab_shndx[sym - info->symtab_start]);
+}
+

/* file2alias.c */
void handle_moddevtable(struct module *mod, struct elf_info *info,

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