objtool: Fix overlapping alternatives

Things like ALTERNATIVE_{2,3}() generate multiple alternatives on the
same place, objtool would override the first orig_alt_group with the
second (or third), failing to check the CFI among all the different
variants.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org> # build only
Tested-by: Thomas Weißschuh <linux@weissschuh.net> # compile and run
Link: https://lore.kernel.org/r/20230208172245.711471461@infradead.org

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 6f0adb2..7e9d3d3 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1744,36 +1744,49 @@ static int handle_group_alt(struct objtool_file *file,
                            struct instruction *orig_insn,
                            struct instruction **new_insn)
 {
-       struct instruction *last_orig_insn, *last_new_insn = NULL, *insn, *nop = NULL;
+       struct instruction *last_new_insn = NULL, *insn, *nop = NULL;
        struct alt_group *orig_alt_group, *new_alt_group;
        unsigned long dest_off;
 
-
-       orig_alt_group = malloc(sizeof(*orig_alt_group));
+       orig_alt_group = orig_insn->alt_group;
        if (!orig_alt_group) {
-               WARN("malloc failed");
-               return -1;
-       }
-       orig_alt_group->cfi = calloc(special_alt->orig_len,
-                                    sizeof(struct cfi_state *));
-       if (!orig_alt_group->cfi) {
-               WARN("calloc failed");
-               return -1;
-       }
+               struct instruction *last_orig_insn = NULL;
 
-       last_orig_insn = NULL;
-       insn = orig_insn;
-       sec_for_each_insn_from(file, insn) {
-               if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
-                       break;
+               orig_alt_group = malloc(sizeof(*orig_alt_group));
+               if (!orig_alt_group) {
+                       WARN("malloc failed");
+                       return -1;
+               }
+               orig_alt_group->cfi = calloc(special_alt->orig_len,
+                                            sizeof(struct cfi_state *));
+               if (!orig_alt_group->cfi) {
+                       WARN("calloc failed");
+                       return -1;
+               }
 
-               insn->alt_group = orig_alt_group;
-               last_orig_insn = insn;
-       }
-       orig_alt_group->orig_group = NULL;
-       orig_alt_group->first_insn = orig_insn;
-       orig_alt_group->last_insn = last_orig_insn;
+               insn = orig_insn;
+               sec_for_each_insn_from(file, insn) {
+                       if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
+                               break;
 
+                       insn->alt_group = orig_alt_group;
+                       last_orig_insn = insn;
+               }
+               orig_alt_group->orig_group = NULL;
+               orig_alt_group->first_insn = orig_insn;
+               orig_alt_group->last_insn = last_orig_insn;
+       } else {
+               if (orig_alt_group->last_insn->offset + orig_alt_group->last_insn->len -
+                   orig_alt_group->first_insn->offset != special_alt->orig_len) {
+                       WARN_FUNC("weirdly overlapping alternative! %ld != %d",
+                                 orig_insn->sec, orig_insn->offset,
+                                 orig_alt_group->last_insn->offset +
+                                 orig_alt_group->last_insn->len -
+                                 orig_alt_group->first_insn->offset,
+                                 special_alt->orig_len);
+                       return -1;
+               }
+       }
 
        new_alt_group = malloc(sizeof(*new_alt_group));
        if (!new_alt_group) {
@@ -1848,7 +1861,7 @@ static int handle_group_alt(struct objtool_file *file,
 
                dest_off = arch_jump_destination(insn);
                if (dest_off == special_alt->new_off + special_alt->new_len) {
-                       insn->jump_dest = next_insn_same_sec(file, last_orig_insn);
+                       insn->jump_dest = next_insn_same_sec(file, orig_alt_group->last_insn);
                        if (!insn->jump_dest) {
                                WARN_FUNC("can't find alternative jump destination",
                                          insn->sec, insn->offset);
@@ -3226,8 +3239,12 @@ static int propagate_alt_cfi(struct objtool_file *file, struct instruction *insn
                alt_cfi[group_off] = insn->cfi;
        } else {
                if (cficmp(alt_cfi[group_off], insn->cfi)) {
-                       WARN_FUNC("stack layout conflict in alternatives",
-                                 insn->sec, insn->offset);
+                       struct alt_group *orig_group = insn->alt_group->orig_group ?: insn->alt_group;
+                       struct instruction *orig = orig_group->first_insn;
+                       char *where = offstr(insn->sec, insn->offset);
+                       WARN_FUNC("stack layout conflict in alternatives: %s",
+                                 orig->sec, orig->offset, where);
+                       free(where);
                        return -1;
                }
        }