Re: objtool crashes on clang output (drivers/hwmon/pmbus/adm1275.o)

[Josh Poimboeuf]

On Thu, Jul 11, 2019 at 02:40:06PM +0200, Arnd Bergmann wrote:
> During randconfig testing with clang-9, I came across an object file
> that makes objtool segfault, see attachment. Let me know if you need
> more information to
> debug this.
> 
> I also get a ton of objtool warnings building random configurations, but Nick
> mentioned that there is still a bug related to asm-goto in the build I'm using
> that may be the root cause. Once I have a fixed clang-9 build, I can have a 
> look
> at those as well.

Seg fault fix:

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 27818a93f0b1..ad18f8ef905a 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -902,7 +902,7 @@ static int add_switch_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 *alt_insn, *prev_insn;
        struct alternative *alt;
        struct symbol *pfunc = insn->func->pfunc;
        unsigned int prev_offset = 0;
@@ -924,6 +924,20 @@ static int add_switch_table(struct objtool_file *file, 
struct instruction *insn,
                if (!alt_insn)
                        break;
 
+               if (!alt_insn->func) {
+                       /*
+                        * Clang 9 has a quirk where a switch table may have
+                        * unused entries in the middle of the table which
+                        * point to just past the end of the function.  They're
+                        * still part of the table but can be ignored.
+                        */
+                       prev_insn = list_prev_entry(alt_insn, list);
+                       if (prev_insn->func && prev_insn->func->pfunc == pfunc)
+                               goto skip;
+
+                       break;
+               }
+
                /* Make sure the jmp dest is in the function or subfunction: */
                if (alt_insn->func->pfunc != pfunc)
                        break;
@@ -936,6 +950,7 @@ static int add_switch_table(struct objtool_file *file, 
struct instruction *insn,
 
                alt->insn = alt_insn;
                list_add_tail(&alt->list, &insn->alts);
+skip:
                prev_offset = rela->offset;
        }