Re: Testing of function/data-sections on linux-2.6.35-rc4

Denys Vlasenko
2010-07-26T00:53:12Z

On Friday 23 July 2010 21:10, Sam Ravnborg wrote:
> >
> > * modpost fix for 64k+ sections: linux-2.6.35-rc4-fs.modpost.patch
> > This patch is in -mm, it still not reach mainline...
> >
>
> Some comments below - but noting fundamental.
>
> + /* Fixup for more than 64k sections */
> + info->num_sections = hdr->e_shnum;
> + if (info->num_sections == 0) { /* more than 64k sections? */
> + /* note: it doesn't need shndx2secindex() */
> + info->num_sections = TO_NATIVE(sechdrs[0].sh_size);
> + }
> I had to read the above twice to get it.
> How about something like this:
>
> /* Fixup for more than 64k sections */
> 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;
> }
>
>
> + info->secindex_strings = hdr->e_shstrndx;
> + if (info->secindex_strings == SHN_XINDEX)
> + info->secindex_strings =
> + shndx2secindex(TO_NATIVE(sechdrs[0].sh_link));
>
> Likewise here...

Done both.

...
> - 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;
>
> Moving this assignnet out of the loop is an unrelated
> but welcome change.

I take you are ok with it?

Please find updated patch below.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
--
vda

--- linux-2.6.35-rc4/scripts/mod/file2alias.c
+++ linux-2.6.35-rc4-fs.modpost/scripts/mod/file2alias.c
@@ -884,16 +884,16 @@
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;
}

--- linux-2.6.35-rc4/scripts/mod/modpost.c
+++ linux-2.6.35-rc4-fs.modpost/scripts/mod/modpost.c
@@ -253,7 +253,7 @@
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 int sec)
{
if (sec == elf->export_sec)
return export_plain;
@@ -373,6 +373,8 @@
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 @@
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 @@
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 @@
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 @@
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 @@
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 @@
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 @@
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 @@
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 @@
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 @@
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 @@
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 @@
}
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 @@
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)
--- linux-2.6.35-rc4/scripts/mod/modpost.h
+++ linux-2.6.35-rc4-fs.modpost/scripts/mod/modpost.h
@@ -129,7 +129,50 @@
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;