linux-kernel - [PATCH v2 13/22] objtool: Refactor function alias logic

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Message-Id: <26a99c31426540f19c9a58b9e10727c385a147bc.1563413318.git.jpoimboe@redhat.com>
Date:   Wed, 17 Jul 2019 20:36:48 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Arnd Bergmann <arnd@...db.de>, Jann Horn <jannh@...gle.com>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: [PATCH v2 13/22] objtool: Refactor function alias logic

- Add an alias check in validate_functions().  With this change, aliases
  no longer need uaccess_safe set.

- Add an alias check in decode_instructions().  With this change, the
  "if (!insn->func)" check is no longer needed.

- Don't create aliases for zero-length functions, as it can have
  unexpected results.  The next patch will spit out a warning for
  zero-length functions anyway.

Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Tested-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
 tools/objtool/check.c | 16 +++++++++-------
 tools/objtool/elf.c   |  2 +-
 2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index bb9cfda670fd..9bf4844d9226 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -276,7 +276,7 @@ static int decode_instructions(struct objtool_file *file)
 		}
 
 		list_for_each_entry(func, &sec->symbol_list, list) {
-			if (func->type != STT_FUNC)
+			if (func->type != STT_FUNC || func->alias != func)
 				continue;
 
 			if (!find_insn(file, sec, func->offset)) {
@@ -286,8 +286,7 @@ static int decode_instructions(struct objtool_file *file)
 			}
 
 			func_for_each_insn(file, func, insn)
-				if (!insn->func)
-					insn->func = func;
+				insn->func = func;
 		}
 	}
 
@@ -508,7 +507,7 @@ static void add_uaccess_safe(struct objtool_file *file)
 		if (!func)
 			continue;
 
-		func->alias->uaccess_safe = true;
+		func->uaccess_safe = true;
 	}
 }
 
@@ -1887,7 +1886,7 @@ static bool insn_state_match(struct instruction *insn, struct insn_state *state)
 static inline bool func_uaccess_safe(struct symbol *func)
 {
 	if (func)
-		return func->alias->uaccess_safe;
+		return func->uaccess_safe;
 
 	return false;
 }
@@ -2355,14 +2354,17 @@ static int validate_functions(struct objtool_file *file)
 
 	for_each_sec(file, sec) {
 		list_for_each_entry(func, &sec->symbol_list, list) {
-			if (func->type != STT_FUNC || func->pfunc != func)
+			if (func->type != STT_FUNC)
+				continue;
+
+			if (func->pfunc != func || func->alias != func)
 				continue;
 
 			insn = find_insn(file, sec, func->offset);
 			if (!insn || insn->ignore || insn->visited)
 				continue;
 
-			state.uaccess = func->alias->uaccess_safe;
+			state.uaccess = func->uaccess_safe;
 
 			ret = validate_branch(file, func, insn, state);
 			if (ret && backtrace)
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index e99e1be19ad9..d2c211b0a5a0 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -278,7 +278,7 @@ static int read_symbols(struct elf *elf)
 			}
 
 			if (sym->offset == s->offset) {
-				if (sym->len == s->len && alias == sym)
+				if (sym->len && sym->len == s->len && alias == sym)
 					alias = s;
 
 				if (sym->len >= s->len) {
-- 
2.20.1