orc_gen.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Copyright (C) 2017 Josh Poimboeuf <[email protected]>
 */

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

#include <linux/objtool_types.h>
#include <asm/orc_types.h>

#include <objtool/check.h>
#include <objtool/orc.h>
#include <objtool/warn.h>

struct orc_list_entry {
	struct list_head list;
	struct orc_entry orc;
	struct section *insn_sec;
	unsigned long insn_off;
};

static int orc_list_add(struct list_head *orc_list, struct orc_entry *orc,
			struct section *sec, unsigned long offset)
{
	struct orc_list_entry *entry = malloc(sizeof(*entry));

	if (!entry) {
		WARN("malloc failed");
		return -1;
	}

	entry->orc	= *orc;
	entry->insn_sec = sec;
	entry->insn_off = offset;

	list_add_tail(&entry->list, orc_list);
	return 0;
}

static unsigned long alt_group_len(struct alt_group *alt_group)
{
	return alt_group->last_insn->offset +
	       alt_group->last_insn->len -
	       alt_group->first_insn->offset;
}

int orc_create(struct objtool_file *file)
{
	struct section *sec, *orc_sec;
	unsigned int nr = 0, idx = 0;
	struct orc_list_entry *entry;
	struct list_head orc_list;

	struct orc_entry null = { .type = ORC_TYPE_UNDEFINED };

	/* Build a deduplicated list of ORC entries: */
	INIT_LIST_HEAD(&orc_list);
	for_each_sec(file->elf, sec) {
		struct orc_entry orc, prev_orc = {0};
		struct instruction *insn;
		bool empty = true;

		if (!sec->text)
			continue;

		sec_for_each_insn(file, sec, insn) {
			struct alt_group *alt_group = insn->alt_group;
			int i;

			if (!alt_group) {
				if (init_orc_entry(&orc, insn->cfi, insn))
					return -1;
				if (!memcmp(&prev_orc, &orc, sizeof(orc)))
					continue;
				if (orc_list_add(&orc_list, &orc, sec,
						 insn->offset))
					return -1;
				nr++;
				prev_orc = orc;
				empty = false;
				continue;
			}

			/*
			 * Alternatives can have different stack layout
			 * possibilities (but they shouldn't conflict).
			 * Instead of traversing the instructions, use the
			 * alt_group's flattened byte-offset-addressed CFI
			 * array.
			 */
			for (i = 0; i < alt_group_len(alt_group); i++) {
				struct cfi_state *cfi = alt_group->cfi[i];
				if (!cfi)
					continue;
				/* errors are reported on the original insn */
				if (init_orc_entry(&orc, cfi, insn))
					return -1;
				if (!memcmp(&prev_orc, &orc, sizeof(orc)))
					continue;
				if (orc_list_add(&orc_list, &orc, insn->sec,
						 insn->offset + i))
					return -1;
				nr++;
				prev_orc = orc;
				empty = false;
			}

			/* Skip to the end of the alt_group */
			insn = alt_group->last_insn;
		}

		/* Add a section terminator */
		if (!empty) {
			orc_list_add(&orc_list, &null, sec, sec->sh.sh_size);
			nr++;
		}
	}
	if (!nr)
		return 0;

	/* Create .orc_unwind, .orc_unwind_ip and .rela.orc_unwind_ip sections: */
	sec = find_section_by_name(file->elf, ".orc_unwind");
	if (sec) {
		WARN("file already has .orc_unwind section, skipping");
		return -1;
	}
	orc_sec = elf_create_section(file->elf, ".orc_unwind",
				     nr * sizeof(struct orc_entry),
				     sizeof(struct orc_entry),
				     SHT_PROGBITS,
				     1,
				     SHF_ALLOC);
	if (!orc_sec)
		return -1;

	sec = elf_create_section_pair(file->elf, ".orc_unwind_ip", sizeof(int), nr, nr);
	if (!sec)
		return -1;

	/* Write ORC entries to sections: */
	list_for_each_entry(entry, &orc_list, list) {
		if (write_orc_entry(file->elf, orc_sec, sec, idx++,
				    entry->insn_sec, entry->insn_off,
				    &entry->orc))
			return -1;
	}

	return 0;
}