linux-kernel - [PATCH 2/3] objtool: Add 'alt

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Message-Id: <f092bae6365f5a4c476b0189b9e3001283117fa2.1608700338.git.jpoimboe@redhat.com>
Date:   Tue, 22 Dec 2020 23:18:09 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Juergen Gross <jgross@...e.com>
Cc:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Miroslav Benes <mbenes@...e.cz>
Subject: [PATCH 2/3] objtool: Add 'alt_group' struct

Create a new struct associated with each group of alternatives
instructions.  This will help with the removal of fake jumps, and more
importantly with adding support for stack layout changes in
alternatives.

Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 tools/objtool/check.c | 29 +++++++++++++++++++++++------
 tools/objtool/check.h | 13 ++++++++++++-
 2 files changed, 35 insertions(+), 7 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index c6ab44543c92..67f39b57c6f7 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -984,20 +984,28 @@ static int handle_group_alt(struct objtool_file *file,
 			    struct instruction *orig_insn,
 			    struct instruction **new_insn)
 {
-	static unsigned int alt_group_next_index = 1;
 	struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
-	unsigned int alt_group = alt_group_next_index++;
+	struct alt_group *orig_alt_group, *new_alt_group;
 	unsigned long dest_off;
 
+
+	orig_alt_group = malloc(sizeof(*orig_alt_group));
+	if (!orig_alt_group) {
+		WARN("malloc failed");
+		return -1;
+	}
 	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;
 
-		insn->alt_group = alt_group;
+		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;
 
 	if (next_insn_same_sec(file, last_orig_insn)) {
 		fake_jump = malloc(sizeof(*fake_jump));
@@ -1028,8 +1036,13 @@ static int handle_group_alt(struct objtool_file *file,
 		return 0;
 	}
 
+	new_alt_group = malloc(sizeof(*new_alt_group));
+	if (!new_alt_group) {
+		WARN("malloc failed");
+		return -1;
+	}
+
 	last_new_insn = NULL;
-	alt_group = alt_group_next_index++;
 	insn = *new_insn;
 	sec_for_each_insn_from(file, insn) {
 		struct reloc *alt_reloc;
@@ -1041,7 +1054,7 @@ static int handle_group_alt(struct objtool_file *file,
 
 		insn->ignore = orig_insn->ignore_alts;
 		insn->func = orig_insn->func;
-		insn->alt_group = alt_group;
+		insn->alt_group = new_alt_group;
 
 		/*
 		 * Since alternative replacement code is copy/pasted by the
@@ -1090,6 +1103,10 @@ static int handle_group_alt(struct objtool_file *file,
 		return -1;
 	}
 
+	new_alt_group->orig_group = orig_alt_group;
+	new_alt_group->first_insn = *new_insn;
+	new_alt_group->last_insn = last_new_insn;
+
 	if (fake_jump)
 		list_add(&fake_jump->list, &last_new_insn->list);
 
@@ -2405,7 +2422,7 @@ static int validate_return(struct symbol *func, struct instruction *insn, struct
 static void fill_alternative_cfi(struct objtool_file *file, struct instruction *insn)
 {
 	struct instruction *first_insn = insn;
-	int alt_group = insn->alt_group;
+	struct alt_group *alt_group = insn->alt_group;
 
 	sec_for_each_insn_continue(file, insn) {
 		if (insn->alt_group != alt_group)
diff --git a/tools/objtool/check.h b/tools/objtool/check.h
index 4c10916ff1cf..b74c383c2d83 100644
--- a/tools/objtool/check.h
+++ b/tools/objtool/check.h
@@ -19,6 +19,17 @@ struct insn_state {
 	s8 instr;
 };
 
+struct alt_group {
+	/*
+	 * Pointer from a replacement group to the original group.  NULL if it
+	 * *is* the original group.
+	 */
+	struct alt_group *orig_group;
+
+	/* First and last instructions in the group */
+	struct instruction *first_insn, *last_insn;
+};
+
 struct instruction {
 	struct list_head list;
 	struct hlist_node hash;
@@ -34,7 +45,7 @@ struct instruction {
 	s8 instr;
 	u8 visited;
 	u8 ret_offset;
-	int alt_group;
+	struct alt_group *alt_group;
 	struct symbol *call_dest;
 	struct instruction *jump_dest;
 	struct instruction *first_jump_src;
-- 
2.29.2