Commit e7c2bc37 authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Thomas Gleixner
Browse files

objtool: Refactor jump table code 



Now that C jump tables are supported, call them "jump tables" instead of
"switch tables".  Also rename some other variables, add comments, and
simplify the code flow a bit.

Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Tested-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/cf951b0c0641628e0b9b81f7ceccd9bcabcb4bd8.1563413318.git.jpoimboe@redhat.com
parent 0c1ddd33

tools/objtool/check.c

+44 −38
Original line number Diff line number Diff line
@@ -627,7 +627,7 @@ static int add_jump_destinations(struct objtool_file *file) 
			 * However this code can't completely replace the

			 * read_symbols() code because this doesn't detect the

			 * case where the parent function's only reference to a

			 * subfunction is through a switch table.

			 * subfunction is through a jump table.

			 */

			if (!strstr(insn->func->name, ".cold.") &&

			    strstr(insn->jump_dest->func->name, ".cold.")) {
@@ -899,20 +899,24 @@ out: 
	return ret;

}



static int add_switch_table(struct objtool_file *file, struct instruction *insn,

static int add_jump_table(struct objtool_file *file, struct instruction *insn,

			    struct rela *table, struct rela *next_table)

{

	struct rela *rela = table;

	struct instruction *alt_insn;

	struct instruction *dest_insn;

	struct alternative *alt;

	struct symbol *pfunc = insn->func->pfunc;

	unsigned int prev_offset = 0;



	list_for_each_entry_from(rela, &table->rela_sec->rela_list, list) {

	/*

	 * Each @rela is a switch table relocation which points to the target

	 * instruction.

	 */

	list_for_each_entry_from(rela, &table->sec->rela_list, list) {

		if (rela == next_table)

			break;



		/* Make sure the switch table entries are consecutive: */

		/* Make sure the table entries are consecutive: */

		if (prev_offset && rela->offset != prev_offset + 8)

			break;
@@ -921,12 +925,12 @@ static int add_switch_table(struct objtool_file *file, struct instruction *insn, 
		    rela->addend == pfunc->offset)

			break;



		alt_insn = find_insn(file, rela->sym->sec, rela->addend);

		if (!alt_insn)

		dest_insn = find_insn(file, rela->sym->sec, rela->addend);

		if (!dest_insn)

			break;



		/* Make sure the jmp dest is in the function or subfunction: */

		if (alt_insn->func->pfunc != pfunc)

		/* Make sure the destination is in the same function: */

		if (dest_insn->func->pfunc != pfunc)

			break;



		alt = malloc(sizeof(*alt));
@@ -935,7 +939,7 @@ static int add_switch_table(struct objtool_file *file, struct instruction *insn, 
			return -1;

		}



		alt->insn = alt_insn;

		alt->insn = dest_insn;

		list_add_tail(&alt->list, &insn->alts);

		prev_offset = rela->offset;

	}
@@ -950,7 +954,7 @@ static int add_switch_table(struct objtool_file *file, struct instruction *insn, 
}



/*

 * find_switch_table() - Given a dynamic jump, find the switch jump table in

 * find_jump_table() - Given a dynamic jump, find the switch jump table in

 * .rodata associated with it.

 *

 * There are 3 basic patterns:
@@ -992,13 +996,13 @@ static int add_switch_table(struct objtool_file *file, struct instruction *insn, 
 *

 *    NOTE: RETPOLINE made it harder still to decode dynamic jumps.

 */

static struct rela *find_switch_table(struct objtool_file *file,

static struct rela *find_jump_table(struct objtool_file *file,

				      struct symbol *func,

				      struct instruction *insn)

{

	struct rela *text_rela, *rodata_rela;

	struct rela *text_rela, *table_rela;

	struct instruction *orig_insn = insn;

	struct section *rodata_sec;

	struct section *table_sec;

	unsigned long table_offset;



	/*
@@ -1031,7 +1035,7 @@ static struct rela *find_switch_table(struct objtool_file *file, 
			continue;



		table_offset = text_rela->addend;

		rodata_sec = text_rela->sym->sec;

		table_sec = text_rela->sym->sec;



		if (text_rela->type == R_X86_64_PC32)

			table_offset += 4;
@@ -1045,29 +1049,31 @@ static struct rela *find_switch_table(struct objtool_file *file, 
		 * need to be placed in the C_JUMP_TABLE_SECTION section.  They

		 * have symbols associated with them.

		 */

		if (find_symbol_containing(rodata_sec, table_offset) &&

		    strcmp(rodata_sec->name, C_JUMP_TABLE_SECTION))

		if (find_symbol_containing(table_sec, table_offset) &&

		    strcmp(table_sec->name, C_JUMP_TABLE_SECTION))

			continue;



		/* Each table entry has a rela associated with it. */

		table_rela = find_rela_by_dest(table_sec, table_offset);

		if (!table_rela)

			continue;



		rodata_rela = find_rela_by_dest(rodata_sec, table_offset);

		if (rodata_rela) {

		/*

		 * Use of RIP-relative switch jumps is quite rare, and

			 * indicates a rare GCC quirk/bug which can leave dead

			 * code behind.

		 * indicates a rare GCC quirk/bug which can leave dead code

		 * behind.

		 */

		if (text_rela->type == R_X86_64_PC32)

			file->ignore_unreachables = true;



			return rodata_rela;

		}

		return table_rela;

	}



	return NULL;

}





static int add_func_switch_tables(struct objtool_file *file,

static int add_func_jump_tables(struct objtool_file *file,

				  struct symbol *func)

{

	struct instruction *insn, *last = NULL, *prev_jump = NULL;
@@ -1080,7 +1086,7 @@ static int add_func_switch_tables(struct objtool_file *file, 


		/*

		 * Store back-pointers for unconditional forward jumps such

		 * that find_switch_table() can back-track using those and

		 * that find_jump_table() can back-track using those and

		 * avoid some potentially confusing code.

		 */

		if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
@@ -1095,17 +1101,17 @@ static int add_func_switch_tables(struct objtool_file *file, 
		if (insn->type != INSN_JUMP_DYNAMIC)

			continue;



		rela = find_switch_table(file, func, insn);

		rela = find_jump_table(file, func, insn);

		if (!rela)

			continue;



		/*

		 * We found a switch table, but we don't know yet how big it

		 * We found a jump table, but we don't know yet how big it

		 * is.  Don't add it until we reach the end of the function or

		 * the beginning of another switch table in the same function.

		 * the beginning of another jump table in the same function.

		 */

		if (prev_jump) {

			ret = add_switch_table(file, prev_jump, prev_rela, rela);

			ret = add_jump_table(file, prev_jump, prev_rela, rela);

			if (ret)

				return ret;

		}
@@ -1115,7 +1121,7 @@ static int add_func_switch_tables(struct objtool_file *file, 
	}



	if (prev_jump) {

		ret = add_switch_table(file, prev_jump, prev_rela, NULL);

		ret = add_jump_table(file, prev_jump, prev_rela, NULL);

		if (ret)

			return ret;

	}
@@ -1128,7 +1134,7 @@ static int add_func_switch_tables(struct objtool_file *file, 
 * section which contains a list of addresses within the function to jump to.

 * This finds these jump tables and adds them to the insn->alts lists.

 */

static int add_switch_table_alts(struct objtool_file *file)

static int add_jump_table_alts(struct objtool_file *file)

{

	struct section *sec;

	struct symbol *func;
@@ -1142,7 +1148,7 @@ static int add_switch_table_alts(struct objtool_file *file) 
			if (func->type != STT_FUNC)

				continue;



			ret = add_func_switch_tables(file, func);

			ret = add_func_jump_tables(file, func);

			if (ret)

				return ret;

		}
@@ -1339,7 +1345,7 @@ static int decode_sections(struct objtool_file *file) 
	if (ret)

		return ret;



	ret = add_switch_table_alts(file);

	ret = add_jump_table_alts(file);

	if (ret)

		return ret;

tools/objtool/elf.c

+1 −1
Original line number Diff line number Diff line
@@ -385,7 +385,7 @@ static int read_relas(struct elf *elf) 
			rela->offset = rela->rela.r_offset;

			symndx = GELF_R_SYM(rela->rela.r_info);

			rela->sym = find_symbol_by_index(elf, symndx);

			rela->rela_sec = sec;

			rela->sec = sec;

			if (!rela->sym) {

				WARN("can't find rela entry symbol %d for %s",

				     symndx, sec->name);

tools/objtool/elf.h

+1 −1
Original line number Diff line number Diff line
@@ -57,7 +57,7 @@ struct rela { 
	struct list_head list;

	struct hlist_node hash;

	GElf_Rela rela;

	struct section *rela_sec;

	struct section *sec;

	struct symbol *sym;

	unsigned int type;

	unsigned long offset;

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