linux-kernel - [RFC][PATCH 4/6] objtool: Read the _THIS_IP

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Message-ID: <20211122170805.211049036@infradead.org>
Date:   Mon, 22 Nov 2021 18:03:05 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     x86@...nel.org, joao@...rdrivepizza.com, hjl.tools@...il.com,
        jpoimboe@...hat.com, andrew.cooper3@...rix.com
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        ndesaulniers@...gle.com, keescook@...omium.org,
        samitolvanen@...gle.com
Subject: [RFC][PATCH 4/6] objtool: Read the _THIS_IP_ hints

Read the new _THIS_IP_ annotation. While there, attempt to not bloat
struct instruction.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 tools/objtool/check.c                 |   27 +++++++++++++++++++++++++++
 tools/objtool/include/objtool/check.h |   13 ++++++++++---
 2 files changed, 37 insertions(+), 3 deletions(-)

--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1854,6 +1854,29 @@ static int read_unwind_hints(struct objt
 	return 0;
 }
 
+static int read_this_ip_hints(struct objtool_file *file)
+{
+	struct section *sec;
+	struct instruction *insn;
+	struct reloc *reloc;
+
+	sec = find_section_by_name(file->elf, ".rela.discard.this_ip");
+	if (!sec)
+		return 0;
+
+	list_for_each_entry(reloc, &sec->reloc_list, list) {
+		insn = find_insn(file, reloc->sym->sec, reloc->sym->offset + reloc->addend);
+		if (!insn) {
+			WARN("bad .discard.this_ip entry");
+			return -1;
+		}
+
+		insn->this_ip = 1;
+	}
+
+	return 0;
+}
+
 static int read_retpoline_hints(struct objtool_file *file)
 {
 	struct section *sec;
@@ -2066,6 +2089,10 @@ static int decode_sections(struct objtoo
 	if (ret)
 		return ret;
 
+	ret = read_this_ip_hints(file);
+	if (ret)
+		return ret;
+
 	/*
 	 * Must be before add_{jump_call}_destination.
 	 */
--- a/tools/objtool/include/objtool/check.h
+++ b/tools/objtool/include/objtool/check.h
@@ -45,11 +45,18 @@ struct instruction {
 	unsigned int len;
 	enum insn_type type;
 	unsigned long immediate;
-	bool dead_end, ignore, ignore_alts;
-	bool hint;
-	bool retpoline_safe;
+
+	u8 dead_end	: 1,
+	   ignore	: 1,
+	   ignore_alts	: 1,
+	   hint		: 1,
+	   retpoline_safe : 1,
+	   this_ip	: 1;
+		/* 2 bit hole */
 	s8 instr;
 	u8 visited;
+	/* u8 hole */
+
 	struct alt_group *alt_group;
 	struct symbol *call_dest;
 	struct instruction *jump_dest;