objtool: Fix sibling call detection in alternatives

In add_jump_destinations(), sibling call detection requires 'insn->func'
to be valid.  But alternative instructions get their 'func' set in
handle_group_alt(), which runs *after* add_jump_destinations().  So
sibling calls in alternatives code don't get properly detected.

Fix that by changing the initialization order: call
add_special_section_alts() *before* add_jump_destinations().

This also means the special case for a missing 'jump_dest' in
add_jump_destinations() can be removed, as it has already been dealt
with.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/c02e0a0a2a4286b5f848d17c77fdcb7e0caf709c.1649718562.git.jpoimboe@redhat.com

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 6f49278..0f5d3de 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1277,6 +1277,13 @@ static int add_jump_destinations(struct objtool_file *file)
        unsigned long dest_off;
 
        for_each_insn(file, insn) {
+               if (insn->jump_dest) {
+                       /*
+                        * handle_group_alt() may have previously set
+                        * 'jump_dest' for some alternatives.
+                        */
+                       continue;
+               }
                if (!is_static_jump(insn))
                        continue;
 
@@ -1308,15 +1315,6 @@ static int add_jump_destinations(struct objtool_file *file)
 
                jump_dest = find_insn(file, dest_sec, dest_off);
                if (!jump_dest) {
-
-                       /*
-                        * This is a special case where an alt instruction
-                        * jumps past the end of the section.  These are
-                        * handled later in handle_group_alt().
-                        */
-                       if (!strcmp(insn->sec->name, ".altinstr_replacement"))
-                               continue;
-
                        WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
                                  insn->sec, insn->offset, dest_sec->name,
                                  dest_off);
@@ -1549,13 +1547,13 @@ static int handle_group_alt(struct objtool_file *file,
                        continue;
 
                dest_off = arch_jump_destination(insn);
-               if (dest_off == special_alt->new_off + special_alt->new_len)
+               if (dest_off == special_alt->new_off + special_alt->new_len) {
                        insn->jump_dest = next_insn_same_sec(file, last_orig_insn);
-
-               if (!insn->jump_dest) {
-                       WARN_FUNC("can't find alternative jump destination",
-                                 insn->sec, insn->offset);
-                       return -1;
+                       if (!insn->jump_dest) {
+                               WARN_FUNC("can't find alternative jump destination",
+                                         insn->sec, insn->offset);
+                               return -1;
+                       }
                }
        }
 
@@ -2254,14 +2252,14 @@ static int decode_sections(struct objtool_file *file)
                return ret;
 
        /*
-        * Must be before add_special_section_alts() as that depends on
-        * jump_dest being set.
+        * Must be before add_jump_destinations(), which depends on 'func'
+        * being set for alternatives, to enable proper sibling call detection.
         */
-       ret = add_jump_destinations(file);
+       ret = add_special_section_alts(file);
        if (ret)
                return ret;
 
-       ret = add_special_section_alts(file);
+       ret = add_jump_destinations(file);
        if (ret)
                return ret;