linux-kernel - [PATCH v2.1 01-B/14] objtool: Uniquely identify alternative instruction groups

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Message-ID: <20200429102101.GK13592@hirez.programming.kicks-ass.net>
Date:   Wed, 29 Apr 2020 12:21:01 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     jpoimboe@...hat.com, alexandre.chartre@...cle.com
Cc:     linux-kernel@...r.kernel.org, jthierry@...hat.com,
        tglx@...utronix.de, x86@...nel.org, mbenes@...e.cz
Subject: [PATCH v2.1 01-B/14] objtool: Uniquely identify alternative
 instruction groups

Subject: objtool: Uniquely identify alternative instruction groups
From: Alexandre Chartre <alexandre.chartre@...cle.com>
Date: Tue, 14 Apr 2020 12:36:11 +0200

From: Alexandre Chartre <alexandre.chartre@...cle.com>

Assign a unique identifier to every alternative instruction group in
order to be able to tell which instructions belong to what
alternative.

[peterz: extracted from a larger patch]
Signed-off-by: Alexandre Chartre <alexandre.chartre@...cle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 tools/objtool/check.c |   26 ++++++++++++++++++++------
 tools/objtool/check.h |    3 ++-
 2 files changed, 22 insertions(+), 7 deletions(-)

--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -770,7 +770,9 @@ static int handle_group_alt(struct objto
 			    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++;
 	unsigned long dest_off;
 
 	last_orig_insn = NULL;
@@ -779,7 +781,7 @@ static int handle_group_alt(struct objto
 		if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
 			break;
 
-		insn->alt_group = true;
+		insn->alt_group = alt_group;
 		last_orig_insn = insn;
 	}
 
@@ -813,6 +815,7 @@ static int handle_group_alt(struct objto
 	}
 
 	last_new_insn = NULL;
+	alt_group = alt_group_next_index++;
 	insn = *new_insn;
 	sec_for_each_insn_from(file, insn) {
 		if (insn->offset >= special_alt->new_off + special_alt->new_len)
@@ -822,6 +825,7 @@ static int handle_group_alt(struct objto
 
 		insn->ignore = orig_insn->ignore_alts;
 		insn->func = orig_insn->func;
+		insn->alt_group = alt_group;
 
 		/*
 		 * Since alternative replacement code is copy/pasted by the
--- a/tools/objtool/check.h
+++ b/tools/objtool/check.h
@@ -30,12 +30,13 @@ struct instruction {
 	unsigned int len;
 	enum insn_type type;
 	unsigned long immediate;
-	bool alt_group, dead_end, ignore, ignore_alts;
+	bool dead_end, ignore, ignore_alts;
 	bool hint;
 	bool retpoline_safe;
 	s8 instr;
 	u8 visited;
 	u8 ret_offset;
+	int alt_group;
 	struct symbol *call_dest;
 	struct instruction *jump_dest;
 	struct instruction *first_jump_src;