[PATCH 22/29] objtool: Support GCC 8 switch tables

From: Greg Kroah-Hartman
Date: Sun Jun 03 2018 - 08:28:43 EST

From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>

commit fd35c88b74170d9335530d9abf271d5d73eb5401 upstream.

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

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@xxxxxxxx>
Reported-by: kbuild test robot <lkp@xxxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: David Laight <David.Laight@xxxxxxxxxx>
Cc: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: damian <damian.tometzki@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/20180510224849.xwi34d6tzheb5wgw@treble
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
tools/objtool/check.c | 24 ++++++++++++++++++++++--
1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 3126760180c4..063afbdec42d 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -805,17 +805,28 @@ 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)

+ /* 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)

/* 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)

alt = malloc(sizeof(*alt));
@@ -826,6 +837,13 @@ 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;
@@ -882,7 +900,9 @@ 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,