Commit b39927cf authored by Sam Ravnborg's avatar Sam Ravnborg

kbuild: check for section mismatch during modpost stage

Section mismatch is identified as references to .init*
sections from non .init sections. And likewise references
to .exit.* sections outside .exit sections.

.init.* sections are discarded after a module is initialized
and references to .init.* sections are oops candidates.
.exit.* sections are discarded when a module is built-in and
thus references to .exit are also oops candidates.

The checks were possible to do using 'make buildcheck' which
called the two perl scripts: reference_discarded.pl and
reference_init.pl. This patch just moves the same functionality
inside modpost and the scripts are then obsoleted.
They will though be kept for a while so users can do double
checks - but note that some .o files are skipped by the perl scripts
so result is not 1:1.
All credit for the concept goes to Keith Owens who implemented
the original perl scrips - this patch just moves it to modpost.

Compared to the perl script the implmentation in modpost will be run
for each kernel build - thus catching the error much sooner, but
the downside is that the individual .o file are not always identified.
Signed-off-by: default avatarSam Ravnborg <sam@ravnborg.org>
parent a67dc21a
......@@ -451,6 +451,262 @@ static char *get_modinfo(void *modinfo, unsigned long modinfo_len,
return NULL;
}
/*
* Find symbols before or equal addr and after addr - in the section sec
**/
static void find_symbols_between(struct elf_info *elf, Elf_Addr addr,
const char *sec,
Elf_Sym **before, Elf_Sym **after)
{
Elf_Sym *sym;
Elf_Ehdr *hdr = elf->hdr;
Elf_Addr beforediff = ~0;
Elf_Addr afterdiff = ~0;
const char *secstrings = (void *)hdr +
elf->sechdrs[hdr->e_shstrndx].sh_offset;
*before = NULL;
*after = NULL;
for (sym = elf->symtab_start; sym < elf->symtab_stop; sym++) {
const char *symsec;
if (sym->st_shndx >= SHN_LORESERVE)
continue;
symsec = secstrings + elf->sechdrs[sym->st_shndx].sh_name;
if (strcmp(symsec, sec) != 0)
continue;
if (sym->st_value <= addr) {
if ((addr - sym->st_value) < beforediff) {
beforediff = addr - sym->st_value;
*before = sym;
}
}
else
{
if ((sym->st_value - addr) < afterdiff) {
afterdiff = sym->st_value - addr;
*after = sym;
}
}
}
}
/**
* Print a warning about a section mismatch.
* Try to find symbols near it so user can find it.
**/
static void warn_sec_mismatch(const char *modname, const char *fromsec,
struct elf_info *elf, Elf_Sym *sym, Elf_Rela r)
{
Elf_Sym *before;
Elf_Sym *after;
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;
find_symbols_between(elf, r.r_offset, fromsec, &before, &after);
if (before && after) {
warn("%s - Section mismatch: reference to %s from %s "
"between '%s' (at offset 0x%lx) and '%s'\n",
modname, secname, fromsec,
elf->strtab + before->st_name,
(long)(r.r_offset - before->st_value),
elf->strtab + after->st_name);
} else if (before) {
warn("%s - Section mismatch: reference to %s from %s "
"after '%s' (at offset 0x%lx)\n",
modname, secname, fromsec,
elf->strtab + before->st_name,
(long)(r.r_offset - before->st_value));
} else if (after) {
warn("%s - Section mismatch: reference to %s from %s "
"before '%s' (at offset -0x%lx)\n",
modname, secname, fromsec,
elf->strtab + before->st_name,
(long)(before->st_value - r.r_offset));
} else {
warn("%s - Section mismatch: reference to %s from %s "
"(offset 0x%lx)\n",
modname, secname, fromsec, (long)r.r_offset);
}
}
/**
* A module includes a number of sections that are discarded
* either when loaded or when used as built-in.
* For loaded modules all functions marked __init and all data
* marked __initdata will be discarded when the module has been intialized.
* Likewise for modules used built-in the sections marked __exit
* are discarded because __exit marked function are supposed to be called
* only when a moduel is unloaded which never happes for built-in modules.
* The check_sec_ref() function traverses all relocation records
* to find all references to a section that reference a section that will
* be discarded and warns about it.
**/
static void check_sec_ref(struct module *mod, const char *modname,
struct elf_info *elf,
int section(const char*),
int section_ref_ok(const char *))
{
int i;
Elf_Sym *sym;
Elf_Ehdr *hdr = elf->hdr;
Elf_Shdr *sechdrs = elf->sechdrs;
const char *secstrings = (void *)hdr +
sechdrs[hdr->e_shstrndx].sh_offset;
/* Walk through all sections */
for (i = 0; i < hdr->e_shnum; i++) {
const char *name = secstrings + sechdrs[i].sh_name +
strlen(".rela");
/* We want to process only relocation sections and not .init */
if (section_ref_ok(name) || (sechdrs[i].sh_type != SHT_RELA))
continue;
Elf_Rela *rela;
Elf_Rela *start = (void *)hdr + sechdrs[i].sh_offset;
Elf_Rela *stop = (void*)start + sechdrs[i].sh_size;
for (rela = start; rela < stop; rela++) {
Elf_Rela r;
const char *secname;
r.r_offset = TO_NATIVE(rela->r_offset);
r.r_info = TO_NATIVE(rela->r_info);
sym = elf->symtab_start + ELF_R_SYM(r.r_info);
secname = secstrings + sechdrs[sym->st_shndx].sh_name;
/* Skip special sections */
if (sym->st_shndx >= SHN_LORESERVE)
continue;
if (section(secname))
warn_sec_mismatch(modname, name, elf, sym, r);
}
}
}
/**
* Functions used only during module init is marked __init and is stored in
* a .init.text section. Likewise data is marked __initdata and stored in
* a .init.data section.
* If this section is one of these sections return 1
* See include/linux/init.h for the details
**/
static int init_section(const char *name)
{
if (strcmp(name, ".init") == 0)
return 1;
if (strncmp(name, ".init.", strlen(".init.")) == 0)
return 1;
return 0;
}
/**
* Identify sections from which references to a .init section is OK.
*
* Unfortunately references to read only data that referenced .init
* sections had to be excluded. Almost all of these are false
* positives, they are created by gcc. The downside of excluding rodata
* is that there really are some user references from rodata to
* init code, e.g. drivers/video/vgacon.c:
*
* const struct consw vga_con = {
* con_startup: vgacon_startup,
*
* where vgacon_startup is __init. If you want to wade through the false
* positives, take out the check for rodata.
**/
static int init_section_ref_ok(const char *name)
{
const char **s;
/* Absolute section names */
const char *namelist1[] = {
".init",
".stab",
".rodata",
".text.lock",
".pci_fixup_header",
".pci_fixup_final",
".pdr",
"__param",
NULL
};
/* Start of section names */
const char *namelist2[] = {
".init.",
".altinstructions",
".eh_frame",
".debug",
NULL
};
for (s = namelist1; *s; s++)
if (strcmp(*s, name) == 0)
return 1;
for (s = namelist2; *s; s++)
if (strncmp(*s, name, strlen(*s)) == 0)
return 1;
return 0;
}
/*
* Functions used only during module exit is marked __exit and is stored in
* a .exit.text section. Likewise data is marked __exitdata and stored in
* a .exit.data section.
* If this section is one of these sections return 1
* See include/linux/init.h for the details
**/
static int exit_section(const char *name)
{
if (strcmp(name, ".exit.text") == 0)
return 1;
if (strcmp(name, ".exit.data") == 0)
return 1;
return 0;
}
/*
* Identify sections from which references to a .exit section is OK.
*
* [OPD] Keith Ownes <kaos@sgi.com> commented:
* For our future {in}sanity, add a comment that this is the ppc .opd
* section, not the ia64 .opd section.
* ia64 .opd should not point to discarded sections.
**/
static int exit_section_ref_ok(const char *name)
{
const char **s;
/* Absolute section names */
const char *namelist1[] = {
".exit.text",
".exit.data",
".init.text",
".opd", /* See comment [OPD] */
".altinstructions",
".pdr",
".exitcall.exit",
".eh_frame",
".stab",
NULL
};
/* Start of section names */
const char *namelist2[] = {
".debug",
NULL
};
for (s = namelist1; *s; s++)
if (strcmp(*s, name) == 0)
return 1;
for (s = namelist2; *s; s++)
if (strncmp(*s, name, strlen(*s)) == 0)
return 1;
return 0;
}
static void read_symbols(char *modname)
{
const char *symname;
......@@ -476,6 +732,8 @@ static void read_symbols(char *modname)
handle_modversions(mod, &info, sym, symname);
handle_moddevtable(mod, &info, sym, symname);
}
check_sec_ref(mod, modname, &info, init_section, init_section_ref_ok);
check_sec_ref(mod, modname, &info, exit_section, exit_section_ref_ok);
version = get_modinfo(info.modinfo, info.modinfo_len, "version");
if (version)
......
......@@ -16,17 +16,27 @@
#define Elf_Ehdr Elf32_Ehdr
#define Elf_Shdr Elf32_Shdr
#define Elf_Sym Elf32_Sym
#define Elf_Addr Elf32_Addr
#define Elf_Section Elf32_Section
#define ELF_ST_BIND ELF32_ST_BIND
#define ELF_ST_TYPE ELF32_ST_TYPE
#define Elf_Rela Elf32_Rela
#define ELF_R_SYM ELF32_R_SYM
#define ELF_R_TYPE ELF32_R_TYPE
#else
#define Elf_Ehdr Elf64_Ehdr
#define Elf_Shdr Elf64_Shdr
#define Elf_Sym Elf64_Sym
#define Elf_Addr Elf64_Addr
#define Elf_Section Elf64_Section
#define ELF_ST_BIND ELF64_ST_BIND
#define ELF_ST_TYPE ELF64_ST_TYPE
#define Elf_Rela Elf64_Rela
#define ELF_R_SYM ELF64_R_SYM
#define ELF_R_TYPE ELF64_R_TYPE
#endif
#if KERNEL_ELFDATA != HOST_ELFDATA
......
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment