Blame kpatch-build/create-klp-module.c

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/*
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 * create-klp-module.c
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 *
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 * This program is free software; you can redistribute it and/or
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 * modify it under the terms of the GNU General Public License
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 * as published by the Free Software Foundation; either version 2
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 * of the License, or (at your option) any later version.
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 *
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 * This program is distributed in the hope that it will be useful,
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 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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 * GNU General Public License for more details.
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 *
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 * You should have received a copy of the GNU General Public License
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 * along with this program; if not, write to the Free Software
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 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA,
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 * 02110-1301, USA.
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 */
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#include <string.h>
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#include <stdlib.h>
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#include <libgen.h>
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#include <argp.h>
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#include "log.h"
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#include "kpatch-elf.h"
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#include "kpatch-intermediate.h"
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/* For log.h */
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char *childobj;
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enum loglevel loglevel = NORMAL;
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/*
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 * Add a symbol from .kpatch.symbols to the symbol table
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 *
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 * If a symbol matching the .kpatch.symbols entry already
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 * exists, return it.
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 */
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static struct symbol *find_or_add_ksym_to_symbols(struct kpatch_elf *kelf,
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						  struct section *ksymsec,
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						  char *strings, int offset)
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{
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	struct kpatch_symbol *ksyms, *ksym;
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	struct symbol *sym;
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	struct rela *rela;
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	char *objname, *name;
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	char pos[32], buf[256];
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	int index;
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	ksyms = ksymsec->data->d_buf;
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	index = offset / sizeof(*ksyms);
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	ksym = &ksyms[index];
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	/* Get name of ksym */
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	rela = find_rela_by_offset(ksymsec->rela,
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				   offset + offsetof(struct kpatch_symbol, name));
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	if (!rela)
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		ERROR("name of ksym not found?");
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	name = strdup(strings + rela->addend);
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	if (!name)
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		ERROR("strdup");
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	/* Get objname of ksym */
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	rela = find_rela_by_offset(ksymsec->rela,
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				   offset + offsetof(struct kpatch_symbol, objname));
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	if (!rela)
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		ERROR("objname of ksym not found?");
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	objname = strdup(strings + rela->addend);
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	if (!objname)
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		ERROR("strdup");
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	snprintf(pos, 32, "%lu", ksym->pos);
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	/* .klp.sym.objname.name,pos */
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	snprintf(buf, 256, KLP_SYM_PREFIX "%s.%s,%s", objname, name, pos);
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	/* Look for an already allocated symbol */
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	list_for_each_entry(sym, &kelf->symbols, list) {
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		if (!strcmp(buf, sym->name))
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			return sym;
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	}
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	ALLOC_LINK(sym, NULL);
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	sym->name = strdup(buf);
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	if (!sym->name)
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		ERROR("strdup");
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	sym->type = ksym->type;
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	sym->bind = ksym->bind;
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	/*
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	 * Note that st_name will be set in kpatch_create_strtab(),
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	 * and sym->index is set in kpatch_reindex_elements()
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	 */
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	sym->sym.st_shndx = SHN_LIVEPATCH;
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	sym->sym.st_info = GELF_ST_INFO(sym->bind, sym->type);
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	/*
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	 * Figure out where to put the new symbol:
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	 *   a) locals need to be grouped together, before globals
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	 *   b) globals can be tacked into the end of the list
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	 */
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	if (is_local_sym(sym)) {
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		struct list_head *head;
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		struct symbol *s;
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		head = &kelf->symbols;
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		list_for_each_entry(s, &kelf->symbols, list) {
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			if (!is_local_sym(s))
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				break;
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			head = &s->list;
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		}
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		list_add_tail(&sym->list, head);
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	} else {
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		list_add_tail(&sym->list, &kelf->symbols);
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	}
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	return sym;
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}
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/*
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 * Create a klp rela section given the base section and objname
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 *
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 * If a klp rela section matching the base section and objname
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 * already exists, return it.
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 */
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static struct section *find_or_add_klp_relasec(struct kpatch_elf *kelf,
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					       struct section *base,
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					       char *objname)
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{
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	struct section  *sec;
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	char buf[256];
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	/* .klp.rela.objname.secname */
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	snprintf(buf, 256, KLP_RELASEC_PREFIX "%s.%s", objname, base->name);
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	list_for_each_entry(sec, &kelf->sections, list) {
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		if (!strcmp(sec->name, buf))
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			return sec;
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	}
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	ALLOC_LINK(sec, &kelf->sections);
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	sec->name = strdup(buf);
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	if (!sec->name)
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		ERROR("strdup");
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	sec->base = base;
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	INIT_LIST_HEAD(&sec->relas);
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	sec->data = malloc(sizeof(*sec->data));
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	if (!sec->data)
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		ERROR("malloc");
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	sec->data->d_type = ELF_T_RELA;
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	/* sh_info and sh_link are set when rebuilding rela sections */
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	sec->sh.sh_type = SHT_RELA;
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	sec->sh.sh_entsize = sizeof(GElf_Rela);
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	sec->sh.sh_addralign = 8;
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	sec->sh.sh_flags = SHF_RELA_LIVEPATCH | SHF_INFO_LINK | SHF_ALLOC;
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	return sec;
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}
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/*
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 * Create klp relocation sections and klp symbols from .kpatch.relocations
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 * and .kpatch.symbols sections
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 *
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 * For every entry in .kpatch.relocations:
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 *   1) Allocate a symbol for the corresponding .kpatch.symbols entry if
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 *      it doesn't already exist (find_or_add_ksym_to_symbols())
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 *      This is the symbol that the relocation points to (rela->sym)
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 *   2) Allocate a rela, and add it to the corresponding .klp.rela. section. If
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 *      the matching .klp.rela. section (given the base section and objname)
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 *      doesn't exist yet, create it (find_or_add_klp_relasec())
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 */
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static void create_klp_relasecs_and_syms(struct kpatch_elf *kelf, struct section *krelasec,
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					 struct section *ksymsec, char *strings)
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{
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	struct section *klp_relasec;
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	struct kpatch_relocation *krelas;
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	struct symbol *sym, *dest;
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	struct rela *rela;
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	char *objname;
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	int nr, index, offset, dest_off;
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	krelas = krelasec->data->d_buf;
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	nr = krelasec->data->d_size / sizeof(*krelas);
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	for (index = 0; index < nr; index++) {
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		offset = index * sizeof(*krelas);
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		/* Get the rela dest sym + offset */
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		rela = find_rela_by_offset(krelasec->rela,
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					   offset + offsetof(struct kpatch_relocation, dest));
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		if (!rela)
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			ERROR("find_rela_by_offset");
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		dest = rela->sym;
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		dest_off = rela->addend;
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		/* Get the name of the object the dest belongs to */
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		rela = find_rela_by_offset(krelasec->rela,
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					   offset + offsetof(struct kpatch_relocation, objname));
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		if (!rela)
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			ERROR("find_rela_by_offset");
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		objname = strdup(strings + rela->addend);
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		if (!objname)
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			ERROR("strdup");
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		/* Get the .kpatch.symbol entry for the rela src */
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		rela = find_rela_by_offset(krelasec->rela,
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					   offset + offsetof(struct kpatch_relocation, ksym));
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		if (!rela)
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			ERROR("find_rela_by_offset");
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		/* Create (or find) a klp symbol from the rela src entry */
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		sym = find_or_add_ksym_to_symbols(kelf, ksymsec, strings, rela->addend);
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		if (!sym)
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			ERROR("error finding or adding ksym to symtab");
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		/* Create (or find) the .klp.rela. section for the dest sec and object */
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		klp_relasec = find_or_add_klp_relasec(kelf, dest->sec, objname);
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		if (!klp_relasec)
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			ERROR("error finding or adding klp relasec");
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		/* Add the klp rela to the .klp.rela. section */
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		ALLOC_LINK(rela, &klp_relasec->relas);
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		rela->offset = dest->sym.st_value + dest_off;
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		rela->type = krelas[index].type;
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		rela->sym = sym;
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		rela->addend = krelas[index].addend;
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	}
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}
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/*
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 * Create .klp.arch. sections by iterating through the .kpatch.arch section
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 *
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 * A .kpatch.arch section is just an array of kpatch_arch structs:
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 *
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 * struct kpatch_arch {
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 *   unsigned long sec;
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 *   char *objname;
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 * };
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 *
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 * There are two relas associated with each kpatch arch entry, one that points
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 * to the section of interest (.parainstructions or .altinstructions), and one
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 * rela points to the name of the object the section belongs to in
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 * .kpatch.strings. This gives us the necessary information to create .klp.arch
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 * sections, which use the '.klp.arch.objname.secname' name format.
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 */
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static void create_klp_arch_sections(struct kpatch_elf *kelf, char *strings)
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{
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	struct section *karch, *sec, *base = NULL;
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	struct kpatch_arch *entries;
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	struct rela *rela, *rela2;
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	char *secname, *objname = NULL;
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	char buf[256];
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	int nr, index, offset, old_size, new_size;
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	karch = find_section_by_name(&kelf->sections, ".kpatch.arch");
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	if (!karch)
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		return;
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	entries = karch->data->d_buf;
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	nr = karch->data->d_size / sizeof(*entries);
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	for (index = 0; index < nr; index++) {
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		offset = index * sizeof(*entries);
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		/* Get the base section (.parainstructions or .altinstructions) */
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		rela = find_rela_by_offset(karch->rela,
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					   offset + offsetof(struct kpatch_arch, sec));
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		if (!rela)
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			ERROR("find_rela_by_offset");
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		base = rela->sym->sec;
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		if (!base)
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			ERROR("base sec of kpatch_arch entry not found");
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		/* Get the name of the object the base section belongs to */
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		rela = find_rela_by_offset(karch->rela,
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					   offset + offsetof(struct kpatch_arch, objname));
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		if (!rela)
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			ERROR("find_rela_by_offset");
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		objname = strdup(strings + rela->addend);
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		if (!objname)
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			ERROR("strdup");
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		/* Example: .klp.arch.vmlinux..parainstructions */
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		snprintf(buf, 256, "%s%s.%s", KLP_ARCH_PREFIX, objname, base->name);
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		/* Check if the .klp.arch. section already exists */
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		sec = find_section_by_name(&kelf->sections, buf);
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		if (!sec) {
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			secname = strdup(buf);
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			if (!secname)
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				ERROR("strdup");
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			/* Start with a new section with size 0 first */
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			sec = create_section_pair(kelf, secname, 1, 0);
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		}
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		/*
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		 * Merge .klp.arch. sections if necessary
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		 *
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		 * Example:
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		 * If there are multiple .parainstructions sections for vmlinux
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		 * (this can happen when, using the --unique option for ld,
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		 * we've linked together multiple .o's with .parainstructions
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		 * sections for the same object), they will be merged under a
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		 * single .klp.arch.vmlinux..parainstructions section
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		 */
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		old_size = sec->data->d_size;
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		/*
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		 * Due to a quirk in how .parainstructions gets linked, the
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		 * section size doesn't encompass the last 4 bytes of the last
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		 * entry.  Align the old size properly before merging.
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		 */
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		if (!strcmp(base->name, ".parainstructions")) {
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			char *str;
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			static int align_mask = 0;
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			if (!align_mask) {
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				str = getenv("PARA_STRUCT_SIZE");
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				if (!str)
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					ERROR("PARA_STRUCT_SIZE not set");
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				align_mask = atoi(str) - 1;
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			}
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			old_size = (old_size + align_mask) & ~align_mask;
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		}
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		new_size = old_size + base->data->d_size;
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		sec->data->d_buf = realloc(sec->data->d_buf, new_size);
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		sec->data->d_size = new_size;
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		sec->sh.sh_size = sec->data->d_size;
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		memcpy(sec->data->d_buf + old_size,
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		       base->data->d_buf, base->data->d_size);
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		list_for_each_entry(rela, &base->rela->relas, list) {
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			ALLOC_LINK(rela2, &sec->rela->relas);
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			rela2->sym = rela->sym;
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			rela2->type = rela->type;
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			rela2->addend = rela->addend;
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			rela2->offset = old_size + rela->offset;
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		}
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	}
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}
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/*
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 * We can't keep these sections since the module loader will apply them before
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 * the patch module gets a chance to load (that's why we copied these sections
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 * into .klp.arch. sections. Hence we remove them here.
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 */
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static void remove_arch_sections(struct kpatch_elf *kelf)
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{
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	size_t i;
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	char *arch_sections[] = {
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		".parainstructions",
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		".rela.parainstructions",
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		".altinstructions",
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		".rela.altinstructions"
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	};
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	for (i = 0; i < sizeof(arch_sections)/sizeof(arch_sections[0]); i++)
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		kpatch_remove_and_free_section(kelf, arch_sections[i]);
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}
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static void remove_intermediate_sections(struct kpatch_elf *kelf)
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{
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	size_t i;
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	char *intermediate_sections[] = {
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		".kpatch.symbols",
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		".rela.kpatch.symbols",
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		".kpatch.relocations",
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		".rela.kpatch.relocations",
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		".kpatch.arch",
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		".rela.kpatch.arch"
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	};
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	for (i = 0; i < sizeof(intermediate_sections)/sizeof(intermediate_sections[0]); i++)
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		kpatch_remove_and_free_section(kelf, intermediate_sections[i]);
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}
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struct arguments {
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	char *args[2];
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	int debug;
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	int no_klp_arch;
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};
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static char args_doc[] = "input.ko output.ko";
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static struct argp_option options[] = {
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	{"debug", 'd', 0, 0, "Show debug output" },
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	{"no-klp-arch-sections", 'n', 0, 0, "Do not output .klp.arch.* sections" },
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	{ 0 }
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};
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static error_t parse_opt (int key, char *arg, struct argp_state *state)
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{
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	/* Get the input argument from argp_parse, which we
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	   know is a pointer to our arguments structure. */
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	struct arguments *arguments = state->input;
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	switch (key)
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	{
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		case 'd':
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			arguments->debug = 1;
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			break;
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		case 'n':
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			arguments->no_klp_arch = 1;
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			break;
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		case ARGP_KEY_ARG:
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			if (state->arg_num >= 2)
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				/* Too many arguments. */
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				argp_usage (state);
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			arguments->args[state->arg_num] = arg;
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			break;
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		case ARGP_KEY_END:
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			if (state->arg_num < 2)
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				/* Not enough arguments. */
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				argp_usage (state);
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			break;
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		default:
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			return ARGP_ERR_UNKNOWN;
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	}
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	return 0;
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}
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static struct argp argp = { options, parse_opt, args_doc, 0 };
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int main(int argc, char *argv[])
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{
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	struct kpatch_elf *kelf;
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	struct section *symtab, *sec;
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	struct section *ksymsec, *krelasec, *strsec;
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	struct arguments arguments;
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	char *strings;
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	int ksyms_nr, krelas_nr;
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	memset(&arguments, 0, sizeof(arguments));
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	argp_parse (&argp, argc, argv, 0, 0, &arguments);
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	if (arguments.debug)
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		loglevel = DEBUG;
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	elf_version(EV_CURRENT);
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	childobj = basename(arguments.args[0]);
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	kelf = kpatch_elf_open(arguments.args[0]);
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	/*
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	 * Sanity checks:
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	 * - Make sure all the required sections exist
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	 * - Make sure that the number of entries in
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	 *   .kpatch.{symbols,relocations} match
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	 */
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	strsec = find_section_by_name(&kelf->sections, ".kpatch.strings");
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	if (!strsec)
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		ERROR("missing .kpatch.strings");
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	strings = strsec->data->d_buf;
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	ksymsec = find_section_by_name(&kelf->sections, ".kpatch.symbols");
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	if (!ksymsec)
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		ERROR("missing .kpatch.symbols section");
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	ksyms_nr = ksymsec->data->d_size / sizeof(struct kpatch_symbol);
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	krelasec = find_section_by_name(&kelf->sections, ".kpatch.relocations");
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	if (!krelasec)
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		ERROR("missing .kpatch.relocations section");
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	krelas_nr = krelasec->data->d_size / sizeof(struct kpatch_relocation);
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	if (krelas_nr != ksyms_nr)
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		ERROR("number of krelas and ksyms do not match");
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	/*
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	 * Create klp rela sections and klp symbols from
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	 * .kpatch.{relocations,symbols} sections
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	 */
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	create_klp_relasecs_and_syms(kelf, krelasec, ksymsec, strings);
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	/*
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	 * If --no-klp-arch-sections wasn't set, additionally
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	 * create .klp.arch. sections
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	 */
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	if (!arguments.no_klp_arch) {
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		create_klp_arch_sections(kelf, strings);
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		remove_arch_sections(kelf);
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	}
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	remove_intermediate_sections(kelf);
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	kpatch_reindex_elements(kelf);
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	/* Rebuild rela sections, new klp rela sections will be rebuilt too. */
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	symtab = find_section_by_name(&kelf->sections, ".symtab");
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	list_for_each_entry(sec, &kelf->sections, list) {
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		if (!is_rela_section(sec))
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			continue;
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		sec->sh.sh_link = symtab->index;
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		sec->sh.sh_info = sec->base->index;
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		kpatch_rebuild_rela_section_data(sec);
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	}
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	kpatch_create_shstrtab(kelf);
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	kpatch_create_strtab(kelf);
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	kpatch_create_symtab(kelf);
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	kpatch_write_output_elf(kelf, kelf->elf, arguments.args[1]);
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	kpatch_elf_teardown(kelf);
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	kpatch_elf_free(kelf);
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	return 0;
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}