linux/tools/objtool/orc_gen.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Copyright (C) 2017 Josh Poimboeuf <jpoimboe@redhat.com>
 */

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

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

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

static int init_orc_entry(struct orc_entry *orc, struct cfi_state *cfi)
{
	struct instruction *insn = container_of(cfi, struct instruction, cfi);
	struct cfi_reg *bp = &cfi->regs[CFI_BP];

	memset(orc, 0, sizeof(*orc));

	orc->end = cfi->end;

	if (cfi->cfa.base == CFI_UNDEFINED) {
		orc->sp_reg = ORC_REG_UNDEFINED;
		return 0;
	}

	switch (cfi->cfa.base) {
	case CFI_SP:
		orc->sp_reg = ORC_REG_SP;
		break;
	case CFI_SP_INDIRECT:
		orc->sp_reg = ORC_REG_SP_INDIRECT;
		break;
	case CFI_BP:
		orc->sp_reg = ORC_REG_BP;
		break;
	case CFI_BP_INDIRECT:
		orc->sp_reg = ORC_REG_BP_INDIRECT;
		break;
	case CFI_R10:
		orc->sp_reg = ORC_REG_R10;
		break;
	case CFI_R13:
		orc->sp_reg = ORC_REG_R13;
		break;
	case CFI_DI:
		orc->sp_reg = ORC_REG_DI;
		break;
	case CFI_DX:
		orc->sp_reg = ORC_REG_DX;
		break;
	default:
		WARN_FUNC("unknown CFA base reg %d",
			  insn->sec, insn->offset, cfi->cfa.base);
		return -1;
	}

	switch (bp->base) {
	case CFI_UNDEFINED:
		orc->bp_reg = ORC_REG_UNDEFINED;
		break;
	case CFI_CFA:
		orc->bp_reg = ORC_REG_PREV_SP;
		break;
	case CFI_BP:
		orc->bp_reg = ORC_REG_BP;
		break;
	default:
		WARN_FUNC("unknown BP base reg %d",
			  insn->sec, insn->offset, bp->base);
		return -1;
	}

	orc->sp_offset = cfi->cfa.offset;
	orc->bp_offset = bp->offset;
	orc->type = cfi->type;

	return 0;
}

static int write_orc_entry(struct elf *elf, struct section *orc_sec,
			   struct section *ip_rsec, unsigned int idx,
			   struct section *insn_sec, unsigned long insn_off,
			   struct orc_entry *o)
{
	struct orc_entry *orc;
	struct reloc *reloc;

	/* populate ORC data */
	orc = (struct orc_entry *)orc_sec->data->d_buf + idx;
	memcpy(orc, o, sizeof(*orc));
	orc->sp_offset = bswap_if_needed(orc->sp_offset);
	orc->bp_offset = bswap_if_needed(orc->bp_offset);

	/* populate reloc for ip */
	reloc = malloc(sizeof(*reloc));
	if (!reloc) {
		perror("malloc");
		return -1;
	}
	memset(reloc, 0, sizeof(*reloc));

	insn_to_reloc_sym_addend(insn_sec, insn_off, reloc);
	if (!reloc->sym) {
		WARN("missing symbol for insn at offset 0x%lx",
		     insn_off);
		return -1;
	}

	reloc->type = R_X86_64_PC32;
	reloc->offset = idx * sizeof(int);
	reloc->sec = ip_rsec;

	elf_add_reloc(elf, reloc);

	return 0;
}

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, *ip_rsec, *orc_sec;
	unsigned int nr = 0, idx = 0;
	struct orc_list_entry *entry;
	struct list_head orc_list;

	struct orc_entry null = {
		.sp_reg  = ORC_REG_UNDEFINED,
		.bp_reg  = ORC_REG_UNDEFINED,
		.type    = UNWIND_HINT_TYPE_CALL,
	};

	/* Build a deduplicated list of ORC entries: */
	INIT_LIST_HEAD(&orc_list);
	for_each_sec(file, 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))
					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;
				if (init_orc_entry(&orc, cfi))
					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->len);
			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", 0,
				     sizeof(struct orc_entry), nr);
	if (!orc_sec)
		return -1;

	sec = elf_create_section(file->elf, ".orc_unwind_ip", 0, sizeof(int), nr);
	if (!sec)
		return -1;
	ip_rsec = elf_create_reloc_section(file->elf, sec, SHT_RELA);
	if (!ip_rsec)
		return -1;

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

	if (elf_rebuild_reloc_section(file->elf, ip_rsec))
		return -1;

	return 0;
}