linux-kernel - [PATCH v3 13/28] objtool: Identify the different types of alternatives

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Message-ID: <20251112160315.2207947-14-alexandre.chartre@oracle.com>
Date: Wed, 12 Nov 2025 17:03:00 +0100
From: Alexandre Chartre <alexandre.chartre@...cle.com>
To: linux-kernel@...r.kernel.org, mingo@...nel.org, jpoimboe@...nel.org,
        peterz@...radead.org
Cc: alexandre.chartre@...cle.com
Subject: [PATCH v3 13/28] objtool: Identify the different types of alternatives

Alternative code, including jump table and exception table, is represented
with the same struct alternative structure. But there is no obvious way to
identify whether the struct represents alternative instructions, a jump
table or an exception table.

So add a type to struct alternative to clearly identify the type of
alternative.

Signed-off-by: Alexandre Chartre <alexandre.chartre@...cle.com>
---
 tools/objtool/check.c                 | 13 ++++++++-----
 tools/objtool/include/objtool/check.h | 12 ++++++++++++
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 26682ac0185ec..93268b7c015e3 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -25,11 +25,6 @@
 #include <linux/static_call_types.h>
 #include <linux/string.h>
 
-struct alternative {
-	struct alternative *next;
-	struct instruction *insn;
-};
-
 static unsigned long nr_cfi, nr_cfi_reused, nr_cfi_cache;
 
 static struct cfi_init_state initial_func_cfi;
@@ -1910,6 +1905,7 @@ static int add_special_section_alts(struct objtool_file *file)
 	struct list_head special_alts;
 	struct instruction *orig_insn, *new_insn;
 	struct special_alt *special_alt, *tmp;
+	enum alternative_type alt_type;
 	struct alternative *alt;
 	int ret;
 
@@ -1948,11 +1944,17 @@ static int add_special_section_alts(struct objtool_file *file)
 			if (ret)
 				return ret;
 
+			alt_type = ALT_TYPE_INSTRUCTIONS;
+
 		} else if (special_alt->jump_or_nop) {
 			ret = handle_jump_alt(file, special_alt, orig_insn,
 					      &new_insn);
 			if (ret)
 				return ret;
+
+			alt_type = ALT_TYPE_JUMP_TABLE;
+		} else {
+			alt_type = ALT_TYPE_EX_TABLE;
 		}
 
 		alt = calloc(1, sizeof(*alt));
@@ -1963,6 +1965,7 @@ static int add_special_section_alts(struct objtool_file *file)
 
 		alt->insn = new_insn;
 		alt->next = orig_insn->alts;
+		alt->type = alt_type;
 		orig_insn->alts = alt;
 
 		list_del(&special_alt->list);
diff --git a/tools/objtool/include/objtool/check.h b/tools/objtool/include/objtool/check.h
index e5f97acb62522..73310c56e91b6 100644
--- a/tools/objtool/include/objtool/check.h
+++ b/tools/objtool/include/objtool/check.h
@@ -38,6 +38,18 @@ struct alt_group {
 	bool ignore;
 };
 
+enum alternative_type {
+	ALT_TYPE_INSTRUCTIONS,
+	ALT_TYPE_JUMP_TABLE,
+	ALT_TYPE_EX_TABLE,
+};
+
+struct alternative {
+	struct alternative *next;
+	struct instruction *insn;
+	enum alternative_type type;
+};
+
 #define INSN_CHUNK_BITS		8
 #define INSN_CHUNK_SIZE		(1 << INSN_CHUNK_BITS)
 #define INSN_CHUNK_MAX		(INSN_CHUNK_SIZE - 1)
-- 
2.43.5