[PATCH 3/3] objtool: Support GCC 8 switch tables

[Josh Poimboeuf]

Add some additional checks to the switch jump table logic.  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 <a...@arndb.de>
Reported-by: kbuild test robot <l...@intel.com>
Signed-off-by: Josh Poimboeuf <jpoim...@redhat.com>
---
 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 14daf6a27d9f..6b6885e1e431 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -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 + sizeof(long))
+                       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);
-- 
2.17.0