Commit fd35c88b authored May 10, 2018 by Josh Poimboeuf Committed by Ingo Molnar May 14, 2018

objtool: Support GCC 8 switch tables

With GCC 8, some issues were found with the objtool switch table
detection.

1) In the .rodata section, immediately after the switch table, there can
be another object which contains a pointer to the function which had
the switch statement. In this case objtool wrongly considers the
function pointer to be part of the switch table. Fix it by:

a) making sure there are no pointers to the beginning of the
function; and

b) making sure there are no gaps in the switch table.

Only the former was needed, the latter adds additional protection for
future optimizations.

2) In find_switch_table(), case 1 and case 2 are missing the check to
ensure that the .rodata switch table data is anonymous, i.e. that it
isn't already associated with an ELF symbol. Fix it by adding the
same find_symbol_containing() check which is used for case 3.

This fixes the following warnings with GCC 8:

drivers/block/virtio_blk.o: warning: objtool: virtio_queue_rq()+0x0: stack state mismatch: cfa1=7+8 cfa2=7+72
net/ipv6/icmp.o: warning: objtool: icmpv6_rcv()+0x0: stack state mismatch: cfa1=7+8 cfa2=7+64
drivers/usb/core/quirks.o: warning: objtool: quirks_param_set()+0x0: stack state mismatch: cfa1=7+8 cfa2=7+48
drivers/mtd/nand/raw/nand_hynix.o: warning: objtool: hynix_nand_decode_id()+0x0: stack state mismatch: cfa1=7+8 cfa2=7+24
drivers/mtd/nand/raw/nand_samsung.o: warning: objtool: samsung_nand_decode_id()+0x0: stack state mismatch: cfa1=7+8 cfa2=7+32
drivers/gpu/drm/nouveau/nvkm/subdev/top/gk104.o: warning: objtool: gk104_top_oneinit()+0x0: stack state mismatch: cfa1=7+8 cfa2=7+64

Reported-by: Arnd Bergmann <arnd@arndb.de>
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: David Laight <David.Laight@ACULAB.COM>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: damian <damian.tometzki@icloud.com>
Link: http://lkml.kernel.org/r/20180510224849.xwi34d6tzheb5wgw@treble

Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 13810435

tools/objtool/check.c

+22 −2

Original line number	Diff line number	Diff line
		@@ -810,17 +810,28 @@ static int add_switch_table(struct objtool_file file, struct instruction insn,
		struct rela *rela = table;
		struct instruction *alt_insn;
		struct alternative *alt;
		struct symbol *pfunc = insn->func->pfunc;
		unsigned int prev_offset = 0;

		list_for_each_entry_from(rela, &file->rodata->rela->rela_list, list) {
		if (rela == next_table)
		break;

		/* Make sure the switch table entries are consecutive: */
		if (prev_offset && rela->offset != prev_offset + 8)
		break;

		/* Detect function pointers from contiguous objects: */
		if (rela->sym->sec == pfunc->sec &&
		rela->addend == pfunc->offset)
		break;

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

		/* Make sure the jmp dest is in the function or subfunction: */
		if (alt_insn->func->pfunc != insn->func->pfunc)
		if (alt_insn->func->pfunc != pfunc)
		break;

		alt = malloc(sizeof(*alt));
		@@ -831,6 +842,13 @@ static int add_switch_table(struct objtool_file file, struct instruction insn,

		alt->insn = alt_insn;
		list_add_tail(&alt->list, &insn->alts);
		prev_offset = rela->offset;
		}

		if (!prev_offset) {
		WARN_FUNC("can't find switch jump table",
		insn->sec, insn->offset);
		return -1;
		}

		return 0;
		@@ -887,7 +905,9 @@ static struct rela find_switch_table(struct objtool_file file,
		struct instruction *orig_insn = insn;

		text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len);
		if (text_rela && text_rela->sym == file->rodata->sym) {
		if (text_rela && text_rela->sym == file->rodata->sym &&
		!find_symbol_containing(file->rodata, text_rela->addend)) {

		/* case 1 */
		rodata_rela = find_rela_by_dest(file->rodata,
		text_rela->addend);

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