objtool: Provide access to feature and flags of group alternatives

Each alternative of a group alternative depends on a specific
feature and flags. Provide access to the feature/flags for each
alternative as an attribute (feature) in struct alt_group.

Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://patch.msgid.link/20251121095340.464045-26-alexandre.chartre@oracle.com

Author: achartre

tools/objtool/check.c

@@ -1751,6 +1751,7 @@ static int handle_group_alt(struct objtool_file *file,
 		orig_alt_group->last_insn = last_orig_insn;
 		orig_alt_group->nop = NULL;
 		orig_alt_group->ignore = orig_insn->ignore_alts;
+		orig_alt_group->feature = 0;
 	} else {
 		if (orig_alt_group->last_insn->offset + orig_alt_group->last_insn->len -
 		    orig_alt_group->first_insn->offset != special_alt->orig_len) {
@@ -1855,6 +1856,7 @@ static int handle_group_alt(struct objtool_file *file,
 	new_alt_group->nop = nop;
 	new_alt_group->ignore = (*new_insn)->ignore_alts;
 	new_alt_group->cfi = orig_alt_group->cfi;
+	new_alt_group->feature = special_alt->feature;
 	return 0;
 }
 

tools/objtool/include/objtool/check.h

@@ -36,6 +36,7 @@ struct alt_group {
 	struct cfi_state **cfi;
 
 	bool ignore;
+	unsigned int feature;
 };
 
 enum alternative_type {

tools/objtool/include/objtool/special.h

@@ -25,7 +25,7 @@ struct special_alt {
 	struct section *new_sec;
 	unsigned long new_off;
 
-	unsigned int orig_len, new_len; /* group only */
+	unsigned int orig_len, new_len, feature; /* group only */
 };
 
 int special_get_alts(struct elf *elf, struct list_head *alts);

tools/objtool/special.c

@@ -81,6 +81,8 @@ static int get_alt_entry(struct elf *elf, const struct special_entry *entry,
 						   entry->orig_len);
 		alt->new_len = *(unsigned char *)(sec->data->d_buf + offset +
 						  entry->new_len);
+		alt->feature = *(unsigned int *)(sec->data->d_buf + offset +
+						 entry->feature);
 	}
 
 	orig_reloc = find_reloc_by_dest(elf, sec, offset + entry->orig);