cregit-Linux how code gets into the kernel

Release 4.18 tools/objtool/special.c

Directory: tools/objtool
/*
 * Copyright (C) 2015 Josh Poimboeuf <jpoimboe@redhat.com>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <http://www.gnu.org/licenses/>.
 */

/*
 * This file reads all the special sections which have alternate instructions
 * which can be patched in or redirected to at runtime.
 */

#include <stdlib.h>
#include <string.h>

#include "special.h"
#include "warn.h"


#define EX_ENTRY_SIZE		12

#define EX_ORIG_OFFSET		0

#define EX_NEW_OFFSET		4


#define JUMP_ENTRY_SIZE		24

#define JUMP_ORIG_OFFSET	0

#define JUMP_NEW_OFFSET		8


#define ALT_ENTRY_SIZE		13

#define ALT_ORIG_OFFSET		0

#define ALT_NEW_OFFSET		4

#define ALT_FEATURE_OFFSET	8

#define ALT_ORIG_LEN_OFFSET	10

#define ALT_NEW_LEN_OFFSET	11


#define X86_FEATURE_POPCNT (4*32+23)


struct special_entry {
	
const char *sec;
	

bool group, jump_or_nop;
	


unsigned char size, orig, new;
	

unsigned char orig_len, new_len; /* group only */
	
unsigned char feature; /* ALTERNATIVE macro CPU feature */
};


struct special_entry entries[] = {
	{
		.sec = ".altinstructions",
		.group = true,
		.size = ALT_ENTRY_SIZE,
		.orig = ALT_ORIG_OFFSET,
		.orig_len = ALT_ORIG_LEN_OFFSET,
		.new = ALT_NEW_OFFSET,
		.new_len = ALT_NEW_LEN_OFFSET,
		.feature = ALT_FEATURE_OFFSET,
        },
	{
		.sec = "__jump_table",
		.jump_or_nop = true,
		.size = JUMP_ENTRY_SIZE,
		.orig = JUMP_ORIG_OFFSET,
		.new = JUMP_NEW_OFFSET,
        },
	{
		.sec = "__ex_table",
		.size = EX_ENTRY_SIZE,
		.orig = EX_ORIG_OFFSET,
		.new = EX_NEW_OFFSET,
        },
	{},
};


static int get_alt_entry(struct elf *elf, struct special_entry *entry, struct section *sec, int idx, struct special_alt *alt) { struct rela *orig_rela, *new_rela; unsigned long offset; offset = idx * entry->size; alt->group = entry->group; alt->jump_or_nop = entry->jump_or_nop; if (alt->group) { alt->orig_len = *(unsigned char *)(sec->data->d_buf + offset + entry->orig_len); alt->new_len = *(unsigned char *)(sec->data->d_buf + offset + entry->new_len); } if (entry->feature) { unsigned short feature; feature = *(unsigned short *)(sec->data->d_buf + offset + entry->feature); /* * It has been requested that we don't validate the !POPCNT * feature path which is a "very very small percentage of * machines". */ if (feature == X86_FEATURE_POPCNT) alt->skip_orig = true; } orig_rela = find_rela_by_dest(sec, offset + entry->orig); if (!orig_rela) { WARN_FUNC("can't find orig rela", sec, offset + entry->orig); return -1; } if (orig_rela->sym->type != STT_SECTION) { WARN_FUNC("don't know how to handle non-section rela symbol %s", sec, offset + entry->orig, orig_rela->sym->name); return -1; } alt->orig_sec = orig_rela->sym->sec; alt->orig_off = orig_rela->addend; if (!entry->group || alt->new_len) { new_rela = find_rela_by_dest(sec, offset + entry->new); if (!new_rela) { WARN_FUNC("can't find new rela", sec, offset + entry->new); return -1; } alt->new_sec = new_rela->sym->sec; alt->new_off = (unsigned int)new_rela->addend; /* _ASM_EXTABLE_EX hack */ if (alt->new_off >= 0x7ffffff0) alt->new_off -= 0x7ffffff0; } return 0; }

Contributors

PersonTokensPropCommitsCommitProp
Josh Poimboeuf348100.00%2100.00%
Total348100.00%2100.00%

/* * Read all the special sections and create a list of special_alt structs which * describe all the alternate instructions which can be patched in or * redirected to at runtime. */
int special_get_alts(struct elf *elf, struct list_head *alts) { struct special_entry *entry; struct section *sec; unsigned int nr_entries; struct special_alt *alt; int idx, ret; INIT_LIST_HEAD(alts); for (entry = entries; entry->sec; entry++) { sec = find_section_by_name(elf, entry->sec); if (!sec) continue; if (sec->len % entry->size != 0) { WARN("%s size not a multiple of %d", sec->name, entry->size); return -1; } nr_entries = sec->len / entry->size; for (idx = 0; idx < nr_entries; idx++) { alt = malloc(sizeof(*alt)); if (!alt) { WARN("malloc failed"); return -1; } memset(alt, 0, sizeof(*alt)); ret = get_alt_entry(elf, entry, sec, idx, alt); if (ret) return ret; list_add_tail(&alt->list, alts); } } return 0; }

Contributors

PersonTokensPropCommitsCommitProp
Josh Poimboeuf207100.00%1100.00%
Total207100.00%1100.00%


Overall Contributors

PersonTokensPropCommitsCommitProp
Josh Poimboeuf757100.00%2100.00%
Total757100.00%2100.00%
Directory: tools/objtool
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