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: Sam Ravnborg <sam@ravnborg.org>
This commit is contained in:
Sam Ravnborg
parent
a67dc21a38
commit
b39927cf4c
2 changed files with 268 additions and 0 deletions
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@ -451,6 +451,262 @@ static char *get_modinfo(void *modinfo, unsigned long modinfo_len,
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return NULL;
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}
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/*
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* Find symbols before or equal addr and after addr - in the section sec
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**/
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static void find_symbols_between(struct elf_info *elf, Elf_Addr addr,
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const char *sec,
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Elf_Sym **before, Elf_Sym **after)
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{
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Elf_Sym *sym;
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Elf_Ehdr *hdr = elf->hdr;
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Elf_Addr beforediff = ~0;
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Elf_Addr afterdiff = ~0;
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const char *secstrings = (void *)hdr +
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elf->sechdrs[hdr->e_shstrndx].sh_offset;
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*before = NULL;
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*after = NULL;
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for (sym = elf->symtab_start; sym < elf->symtab_stop; sym++) {
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const char *symsec;
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if (sym->st_shndx >= SHN_LORESERVE)
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continue;
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symsec = secstrings + elf->sechdrs[sym->st_shndx].sh_name;
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if (strcmp(symsec, sec) != 0)
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continue;
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if (sym->st_value <= addr) {
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if ((addr - sym->st_value) < beforediff) {
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beforediff = addr - sym->st_value;
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*before = sym;
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}
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}
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else
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{
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if ((sym->st_value - addr) < afterdiff) {
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afterdiff = sym->st_value - addr;
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*after = sym;
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}
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}
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}
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}
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/**
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* Print a warning about a section mismatch.
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* Try to find symbols near it so user can find it.
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**/
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static void warn_sec_mismatch(const char *modname, const char *fromsec,
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struct elf_info *elf, Elf_Sym *sym, Elf_Rela r)
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{
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Elf_Sym *before;
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Elf_Sym *after;
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Elf_Ehdr *hdr = elf->hdr;
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Elf_Shdr *sechdrs = elf->sechdrs;
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const char *secstrings = (void *)hdr +
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sechdrs[hdr->e_shstrndx].sh_offset;
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const char *secname = secstrings + sechdrs[sym->st_shndx].sh_name;
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find_symbols_between(elf, r.r_offset, fromsec, &before, &after);
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if (before && after) {
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warn("%s - Section mismatch: reference to %s from %s "
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"between '%s' (at offset 0x%lx) and '%s'\n",
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modname, secname, fromsec,
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elf->strtab + before->st_name,
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(long)(r.r_offset - before->st_value),
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elf->strtab + after->st_name);
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} else if (before) {
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warn("%s - Section mismatch: reference to %s from %s "
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"after '%s' (at offset 0x%lx)\n",
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modname, secname, fromsec,
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elf->strtab + before->st_name,
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(long)(r.r_offset - before->st_value));
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} else if (after) {
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warn("%s - Section mismatch: reference to %s from %s "
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"before '%s' (at offset -0x%lx)\n",
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modname, secname, fromsec,
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elf->strtab + before->st_name,
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(long)(before->st_value - r.r_offset));
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} else {
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warn("%s - Section mismatch: reference to %s from %s "
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"(offset 0x%lx)\n",
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modname, secname, fromsec, (long)r.r_offset);
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}
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}
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/**
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* A module includes a number of sections that are discarded
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* either when loaded or when used as built-in.
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* For loaded modules all functions marked __init and all data
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* marked __initdata will be discarded when the module has been intialized.
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* Likewise for modules used built-in the sections marked __exit
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* are discarded because __exit marked function are supposed to be called
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* only when a moduel is unloaded which never happes for built-in modules.
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* The check_sec_ref() function traverses all relocation records
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* to find all references to a section that reference a section that will
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* be discarded and warns about it.
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**/
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static void check_sec_ref(struct module *mod, const char *modname,
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struct elf_info *elf,
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int section(const char*),
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int section_ref_ok(const char *))
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{
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int i;
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Elf_Sym *sym;
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Elf_Ehdr *hdr = elf->hdr;
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Elf_Shdr *sechdrs = elf->sechdrs;
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const char *secstrings = (void *)hdr +
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sechdrs[hdr->e_shstrndx].sh_offset;
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/* Walk through all sections */
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for (i = 0; i < hdr->e_shnum; i++) {
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const char *name = secstrings + sechdrs[i].sh_name +
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strlen(".rela");
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/* We want to process only relocation sections and not .init */
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if (section_ref_ok(name) || (sechdrs[i].sh_type != SHT_RELA))
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continue;
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Elf_Rela *rela;
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Elf_Rela *start = (void *)hdr + sechdrs[i].sh_offset;
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Elf_Rela *stop = (void*)start + sechdrs[i].sh_size;
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for (rela = start; rela < stop; rela++) {
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Elf_Rela r;
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const char *secname;
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r.r_offset = TO_NATIVE(rela->r_offset);
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r.r_info = TO_NATIVE(rela->r_info);
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sym = elf->symtab_start + ELF_R_SYM(r.r_info);
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secname = secstrings + sechdrs[sym->st_shndx].sh_name;
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/* Skip special sections */
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if (sym->st_shndx >= SHN_LORESERVE)
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continue;
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if (section(secname))
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warn_sec_mismatch(modname, name, elf, sym, r);
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}
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}
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}
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/**
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* Functions used only during module init is marked __init and is stored in
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* a .init.text section. Likewise data is marked __initdata and stored in
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* a .init.data section.
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* If this section is one of these sections return 1
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* See include/linux/init.h for the details
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**/
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static int init_section(const char *name)
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{
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if (strcmp(name, ".init") == 0)
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return 1;
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if (strncmp(name, ".init.", strlen(".init.")) == 0)
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return 1;
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return 0;
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}
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/**
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* Identify sections from which references to a .init section is OK.
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*
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* Unfortunately references to read only data that referenced .init
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* sections had to be excluded. Almost all of these are false
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* positives, they are created by gcc. The downside of excluding rodata
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* is that there really are some user references from rodata to
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* init code, e.g. drivers/video/vgacon.c:
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*
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* const struct consw vga_con = {
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* con_startup: vgacon_startup,
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*
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* where vgacon_startup is __init. If you want to wade through the false
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* positives, take out the check for rodata.
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**/
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static int init_section_ref_ok(const char *name)
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{
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const char **s;
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/* Absolute section names */
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const char *namelist1[] = {
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".init",
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".stab",
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".rodata",
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".text.lock",
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".pci_fixup_header",
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".pci_fixup_final",
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".pdr",
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"__param",
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NULL
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};
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/* Start of section names */
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const char *namelist2[] = {
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".init.",
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".altinstructions",
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".eh_frame",
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".debug",
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NULL
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};
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for (s = namelist1; *s; s++)
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if (strcmp(*s, name) == 0)
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return 1;
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for (s = namelist2; *s; s++)
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if (strncmp(*s, name, strlen(*s)) == 0)
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return 1;
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return 0;
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}
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/*
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* Functions used only during module exit is marked __exit and is stored in
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* a .exit.text section. Likewise data is marked __exitdata and stored in
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* a .exit.data section.
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* If this section is one of these sections return 1
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* See include/linux/init.h for the details
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**/
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static int exit_section(const char *name)
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{
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if (strcmp(name, ".exit.text") == 0)
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return 1;
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if (strcmp(name, ".exit.data") == 0)
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return 1;
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return 0;
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}
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/*
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* Identify sections from which references to a .exit section is OK.
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*
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* [OPD] Keith Ownes <kaos@sgi.com> commented:
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* For our future {in}sanity, add a comment that this is the ppc .opd
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* section, not the ia64 .opd section.
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* ia64 .opd should not point to discarded sections.
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**/
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static int exit_section_ref_ok(const char *name)
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{
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const char **s;
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/* Absolute section names */
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const char *namelist1[] = {
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".exit.text",
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".exit.data",
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".init.text",
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".opd", /* See comment [OPD] */
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".altinstructions",
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".pdr",
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".exitcall.exit",
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".eh_frame",
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".stab",
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NULL
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};
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/* Start of section names */
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const char *namelist2[] = {
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".debug",
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NULL
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};
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for (s = namelist1; *s; s++)
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if (strcmp(*s, name) == 0)
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return 1;
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for (s = namelist2; *s; s++)
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if (strncmp(*s, name, strlen(*s)) == 0)
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return 1;
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return 0;
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}
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static void read_symbols(char *modname)
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{
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const char *symname;
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@ -476,6 +732,8 @@ static void read_symbols(char *modname)
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handle_modversions(mod, &info, sym, symname);
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handle_moddevtable(mod, &info, sym, symname);
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}
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check_sec_ref(mod, modname, &info, init_section, init_section_ref_ok);
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check_sec_ref(mod, modname, &info, exit_section, exit_section_ref_ok);
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version = get_modinfo(info.modinfo, info.modinfo_len, "version");
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if (version)
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@ -16,17 +16,27 @@
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#define Elf_Ehdr Elf32_Ehdr
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#define Elf_Shdr Elf32_Shdr
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#define Elf_Sym Elf32_Sym
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#define Elf_Addr Elf32_Addr
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#define Elf_Section Elf32_Section
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#define ELF_ST_BIND ELF32_ST_BIND
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#define ELF_ST_TYPE ELF32_ST_TYPE
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#define Elf_Rela Elf32_Rela
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#define ELF_R_SYM ELF32_R_SYM
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#define ELF_R_TYPE ELF32_R_TYPE
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#else
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#define Elf_Ehdr Elf64_Ehdr
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#define Elf_Shdr Elf64_Shdr
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#define Elf_Sym Elf64_Sym
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#define Elf_Addr Elf64_Addr
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#define Elf_Section Elf64_Section
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#define ELF_ST_BIND ELF64_ST_BIND
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#define ELF_ST_TYPE ELF64_ST_TYPE
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#define Elf_Rela Elf64_Rela
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#define ELF_R_SYM ELF64_R_SYM
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#define ELF_R_TYPE ELF64_R_TYPE
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#endif
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#if KERNEL_ELFDATA != HOST_ELFDATA
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