linux-kernel - [RFC][PATCH 13/17] objtool/x86: Add arch_is_offset

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Message-ID: <20230809072201.326960605@infradead.org>
Date:   Wed, 09 Aug 2023 09:12:31 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        David.Kaplan@....com, Andrew.Cooper3@...rix.com,
        jpoimboe@...nel.org, gregkh@...uxfoundation.org
Subject: [RFC][PATCH 13/17] objtool/x86: Add arch_is_offset_insn()

Add a little wrappery to identify the magic symbols that are actually
inside another instruction -- yay for variable length instruction
encoding.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 tools/objtool/arch/x86/decode.c      |    6 ++++++
 tools/objtool/check.c                |   13 ++++++++++---
 tools/objtool/include/objtool/arch.h |    1 +
 tools/objtool/include/objtool/elf.h  |    1 +
 4 files changed, 18 insertions(+), 3 deletions(-)

--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -826,3 +826,9 @@ bool arch_is_rethunk(struct symbol *sym)
 {
 	return !strcmp(sym->name, "__x86_return_thunk");
 }
+
+bool arch_is_offset_insn(struct symbol *sym)
+{
+	return !strcmp(sym->name, "zen_return_thunk") ||
+	       !strcmp(sym->name, "srso_safe_ret");
+}
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -459,8 +459,7 @@ static int decode_instructions(struct ob
 			 * Both zen_return_thunk() and srso_safe_ret() are embedded inside
 			 * another instruction and objtool doesn't grok that. Skip validating them.
 			 */
-			if (!strcmp(func->name, "zen_return_thunk") ||
-			    !strcmp(func->name, "srso_safe_ret") || func->alias != func)
+			if (func->offset_insn || func->alias != func)
 				continue;
 
 			if (!find_insn(file, sec, func->offset)) {
@@ -1303,6 +1302,11 @@ __weak bool arch_is_rethunk(struct symbo
 	return false;
 }
 
+__weak bool arch_is_offset_insn(struct symbol *sym)
+{
+	return false;
+}
+
 static struct reloc *insn_reloc(struct objtool_file *file, struct instruction *insn)
 {
 	struct reloc *reloc;
@@ -1588,7 +1592,7 @@ static int add_jump_destinations(struct
 			 * middle of another instruction.  Objtool only
 			 * knows about the outer instruction.
 			 */
-			if (sym && !strcmp(sym->name, "zen_return_thunk")) {
+			if (sym && sym->offset_insn) {
 				add_return_call(file, insn, false);
 				continue;
 			}
@@ -2507,6 +2511,9 @@ static int classify_symbols(struct objto
 		if (arch_is_rethunk(func))
 			func->return_thunk = true;
 
+		if (arch_is_offset_insn(func))
+			func->offset_insn = true;
+
 		if (arch_ftrace_match(func->name))
 			func->fentry = true;
 
--- a/tools/objtool/include/objtool/arch.h
+++ b/tools/objtool/include/objtool/arch.h
@@ -90,6 +90,7 @@ int arch_decode_hint_reg(u8 sp_reg, int
 
 bool arch_is_retpoline(struct symbol *sym);
 bool arch_is_rethunk(struct symbol *sym);
+bool arch_is_offset_insn(struct symbol *sym);
 
 int arch_rewrite_retpolines(struct objtool_file *file);
 
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -66,6 +66,7 @@ struct symbol {
 	u8 fentry            : 1;
 	u8 profiling_func    : 1;
 	u8 warned	     : 1;
+	u8 offset_insn       : 1;
 	struct list_head pv_target;
 	struct reloc *relocs;
 };