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modpost: extract symbol versions from *.cmd files
Currently, CONFIG_MODVERSIONS needs extra link to embed the symbol versions into ELF objects. Then, modpost extracts the version CRCs from them. The following figures show how it currently works, and how I am trying to change it. Current implementation ====================== |----------| embed CRC -------------------------->| final | $(CC) $(LD) / |---------| | link for | -----> *.o -------> *.o -->| modpost | | vmlinux | / / | |-- *.mod.c -->| or | / genksyms / |---------| | module | *.c ------> *.symversions |----------| Genksyms outputs the calculated CRCs in the form of linker script (*.symversions), which is used by $(LD) to update the object. If CONFIG_LTO_CLANG=y, the build process is much more complex. Embedding the CRCs is postponed until the LLVM bitcode is converted into ELF, creating another intermediate *.prelink.o. However, this complexity is unneeded. There is no reason why we must embed version CRCs in objects so early. There is final link stage for vmlinux (scripts/link-vmlinux.sh) and modules (scripts/Makefile.modfinal). We can link CRCs at the very last moment. New implementation ================== |----------| --------------------------------------->| final | $(CC) / |---------| | link for | -----> *.o ---->| | | vmlinux | / | modpost |--- .vmlinux.export.c -->| or | / genksyms | |--- *.mod.c ------------>| module | *.c ------> *.cmd -->|---------| |----------| Pass the symbol versions to modpost as separate text data, which are available in *.cmd files. This commit changes modpost to extract CRCs from *.cmd files instead of from ELF objects. Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> Reviewed-by: Nicolas Schier <nicolas@fjasle.eu> Tested-by: Nathan Chancellor <nathan@kernel.org> Reviewed-by: Sami Tolvanen <samitolvanen@google.com> Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # LLVM-14 (x86-64)
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@ -383,19 +383,10 @@ static struct symbol *sym_add_exported(const char *name, struct module *mod,
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return s;
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}
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static void sym_set_crc(const char *name, unsigned int crc)
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static void sym_set_crc(struct symbol *sym, unsigned int crc)
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{
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struct symbol *s = find_symbol(name);
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/*
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* Ignore stand-alone __crc_*, which might be auto-generated symbols
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* such as __*_veneer in ARM ELF.
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*/
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if (!s)
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return;
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s->crc = crc;
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s->crc_valid = true;
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sym->crc = crc;
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sym->crc_valid = true;
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}
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static void *grab_file(const char *filename, size_t *size)
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@ -618,33 +609,6 @@ static int ignore_undef_symbol(struct elf_info *info, const char *symname)
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return 0;
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}
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static void handle_modversion(const struct module *mod,
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const struct elf_info *info,
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const Elf_Sym *sym, const char *symname)
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{
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unsigned int crc;
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if (sym->st_shndx == SHN_UNDEF) {
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warn("EXPORT symbol \"%s\" [%s%s] version generation failed, symbol will not be versioned.\n"
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"Is \"%s\" prototyped in <asm/asm-prototypes.h>?\n",
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symname, mod->name, mod->is_vmlinux ? "" : ".ko",
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symname);
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return;
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}
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if (sym->st_shndx == SHN_ABS) {
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crc = sym->st_value;
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} else {
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unsigned int *crcp;
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/* symbol points to the CRC in the ELF object */
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crcp = sym_get_data(info, sym);
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crc = TO_NATIVE(*crcp);
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}
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sym_set_crc(symname, crc);
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}
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static void handle_symbol(struct module *mod, struct elf_info *info,
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const Elf_Sym *sym, const char *symname)
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{
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@ -1952,6 +1916,104 @@ static char *remove_dot(char *s)
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return s;
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}
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/*
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* The CRCs are recorded in .*.cmd files in the form of:
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* #SYMVER <name> <crc>
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*/
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static void extract_crcs_for_object(const char *object, struct module *mod)
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{
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char cmd_file[PATH_MAX];
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char *buf, *p;
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const char *base;
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int dirlen, ret;
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base = strrchr(object, '/');
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if (base) {
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base++;
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dirlen = base - object;
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} else {
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dirlen = 0;
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base = object;
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}
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ret = snprintf(cmd_file, sizeof(cmd_file), "%.*s.%s.cmd",
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dirlen, object, base);
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if (ret >= sizeof(cmd_file)) {
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error("%s: too long path was truncated\n", cmd_file);
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return;
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}
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buf = read_text_file(cmd_file);
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p = buf;
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while ((p = strstr(p, "\n#SYMVER "))) {
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char *name;
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size_t namelen;
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unsigned int crc;
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struct symbol *sym;
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name = p + strlen("\n#SYMVER ");
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p = strchr(name, ' ');
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if (!p)
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break;
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namelen = p - name;
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p++;
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if (!isdigit(*p))
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continue; /* skip this line */
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crc = strtol(p, &p, 0);
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if (*p != '\n')
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continue; /* skip this line */
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name[namelen] = '\0';
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/*
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* sym_find_with_module() may return NULL here.
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* It typically occurs when CONFIG_TRIM_UNUSED_KSYMS=y.
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* Since commit e1327a127703, genksyms calculates CRCs of all
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* symbols, including trimmed ones. Ignore orphan CRCs.
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*/
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sym = sym_find_with_module(name, mod);
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if (sym)
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sym_set_crc(sym, crc);
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}
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free(buf);
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}
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/*
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* The symbol versions (CRC) are recorded in the .*.cmd files.
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* Parse them to retrieve CRCs for the current module.
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*/
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static void mod_set_crcs(struct module *mod)
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{
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char objlist[PATH_MAX];
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char *buf, *p, *obj;
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int ret;
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if (mod->is_vmlinux) {
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strcpy(objlist, ".vmlinux.objs");
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} else {
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/* objects for a module are listed in the *.mod file. */
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ret = snprintf(objlist, sizeof(objlist), "%s.mod", mod->name);
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if (ret >= sizeof(objlist)) {
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error("%s: too long path was truncated\n", objlist);
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return;
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}
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}
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buf = read_text_file(objlist);
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p = buf;
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while ((obj = strsep(&p, "\n")) && obj[0])
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extract_crcs_for_object(obj, mod);
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free(buf);
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}
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static void read_symbols(const char *modname)
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{
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const char *symname;
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@ -2012,9 +2074,6 @@ static void read_symbols(const char *modname)
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if (strstarts(symname, "__kstrtabns_"))
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sym_update_namespace(symname + strlen("__kstrtabns_"),
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sym_get_data(&info, sym));
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if (strstarts(symname, "__crc_"))
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handle_modversion(mod, &info, sym,
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symname + strlen("__crc_"));
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}
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// check for static EXPORT_SYMBOL_* functions && global vars
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@ -2042,12 +2101,17 @@ static void read_symbols(const char *modname)
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parse_elf_finish(&info);
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/* Our trick to get versioning for module struct etc. - it's
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* never passed as an argument to an exported function, so
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* the automatic versioning doesn't pick it up, but it's really
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* important anyhow */
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if (modversions)
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if (modversions) {
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/*
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* Our trick to get versioning for module struct etc. - it's
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* never passed as an argument to an exported function, so
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* the automatic versioning doesn't pick it up, but it's really
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* important anyhow.
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*/
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sym_add_unresolved("module_layout", mod, false);
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mod_set_crcs(mod);
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}
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}
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static void read_symbols_from_files(const char *filename)
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@ -2204,6 +2268,23 @@ static void add_header(struct buffer *b, struct module *mod)
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buf_printf(b, "\nMODULE_INFO(staging, \"Y\");\n");
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}
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static void check_symversions(struct module *mod)
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{
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struct symbol *sym;
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if (!modversions)
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return;
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list_for_each_entry(sym, &mod->exported_symbols, list) {
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if (!sym->crc_valid) {
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warn("EXPORT symbol \"%s\" [%s%s] version generation failed, symbol will not be versioned.\n"
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"Is \"%s\" prototyped in <asm/asm-prototypes.h>?\n",
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sym->name, mod->name, mod->is_vmlinux ? "" : ".ko",
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sym->name);
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}
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}
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}
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/**
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* Record CRCs for unresolved symbols
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**/
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@ -2419,7 +2500,7 @@ static void read_dump(const char *fname)
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}
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s = sym_add_exported(symname, mod, gpl_only);
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s->is_static = false;
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sym_set_crc(symname, crc);
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sym_set_crc(s, crc);
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sym_update_namespace(symname, namespace);
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}
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free(buf);
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if (mod->from_dump)
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continue;
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check_symversions(mod);
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if (!mod->is_vmlinux)
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write_mod_c_file(mod);
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}
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