linux-kernel - [PATCH v2 27/62] objtool: Mark .cold subfunctions

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Message-ID: <d67ebbcb2d1da07b08ba3e2d43339b857a874b40.1746821544.git.jpoimboe@kernel.org>
Date: Fri,  9 May 2025 13:16:51 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org,
	Petr Mladek <pmladek@...e.com>,
	Miroslav Benes <mbenes@...e.cz>,
	Joe Lawrence <joe.lawrence@...hat.com>,
	live-patching@...r.kernel.org,
	Song Liu <song@...nel.org>,
	laokz <laokz@...mail.com>,
	Jiri Kosina <jikos@...nel.org>,
	Marcos Paulo de Souza <mpdesouza@...e.com>,
	Weinan Liu <wnliu@...gle.com>,
	Fazla Mehrab <a.mehrab@...edance.com>,
	Chen Zhongjin <chenzhongjin@...wei.com>,
	Puranjay Mohan <puranjay@...nel.org>
Subject: [PATCH v2 27/62] objtool: Mark .cold subfunctions

Introduce a flag to identify .cold subfunctions so they can be detected
easier and faster.

Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
 tools/objtool/check.c               | 14 ++++++--------
 tools/objtool/elf.c                 | 19 ++++++++++---------
 tools/objtool/include/objtool/elf.h |  1 +
 3 files changed, 17 insertions(+), 17 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index d53438865d68..043c36b70f26 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1581,7 +1581,9 @@ static int add_jump_destinations(struct objtool_file *file)
 		/*
 		 * Cross-function jump.
 		 */
-		if (func && insn_func(jump_dest) && func != insn_func(jump_dest)) {
+
+		if (func && insn_func(jump_dest) && !func->cold &&
+		    insn_func(jump_dest)->cold) {
 
 			/*
 			 * For GCC 8+, create parent/child links for any cold
@@ -1598,11 +1600,8 @@ static int add_jump_destinations(struct objtool_file *file)
 			 * case where the parent function's only reference to a
 			 * subfunction is through a jump table.
 			 */
-			if (!strstr(func->name, ".cold") &&
-			    strstr(insn_func(jump_dest)->name, ".cold")) {
-				func->cfunc = insn_func(jump_dest);
-				insn_func(jump_dest)->pfunc = func;
-			}
+			func->cfunc = insn_func(jump_dest);
+			insn_func(jump_dest)->pfunc = func;
 		}
 
 		if (jump_is_sibling_call(file, insn, jump_dest)) {
@@ -4066,9 +4065,8 @@ static bool ignore_unreachable_insn(struct objtool_file *file, struct instructio
 			 * If this hole jumps to a .cold function, mark it ignore too.
 			 */
 			if (insn->jump_dest && insn_func(insn->jump_dest) &&
-			    strstr(insn_func(insn->jump_dest)->name, ".cold")) {
+			    insn_func(insn->jump_dest)->cold)
 				insn_func(insn->jump_dest)->ignore = true;
-			}
 		}
 
 		return false;
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index d36c0d42fd7b..59568381486c 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -441,6 +441,10 @@ static void elf_add_symbol(struct elf *elf, struct symbol *sym)
 	list_add(&sym->list, entry);
 	elf_hash_add(symbol, &sym->hash, sym->idx);
 	elf_hash_add(symbol_name, &sym->name_hash, str_hash(sym->name));
+
+	if (is_func_sym(sym) && strstr(sym->name, ".cold"))
+		sym->cold = 1;
+	sym->pfunc = sym->cfunc = sym;
 }
 
 static int read_symbols(struct elf *elf)
@@ -527,18 +531,15 @@ static int read_symbols(struct elf *elf)
 		sec_for_each_sym(sec, sym) {
 			char *pname;
 			size_t pnamelen;
-			if (!is_func_sym(sym))
+
+			if (!sym->cold)
 				continue;
 
-			if (sym->pfunc == NULL)
-				sym->pfunc = sym;
-
-			if (sym->cfunc == NULL)
-				sym->cfunc = sym;
-
 			coldstr = strstr(sym->name, ".cold");
-			if (!coldstr)
-				continue;
+			if (!coldstr) {
+				ERROR("%s(): cold subfunction without \".cold\"?", sym->name);
+				return -1;
+			}
 
 			pnamelen = coldstr - sym->name;
 			pname = strndup(sym->name, pnamelen);
diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index 0914dadece0b..f41496b0ad8f 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -71,6 +71,7 @@ struct symbol {
 	u8 local_label       : 1;
 	u8 frame_pointer     : 1;
 	u8 ignore	     : 1;
+	u8 cold		     : 1;
 	struct list_head pv_target;
 	struct reloc *relocs;
 	struct section *group_sec;
-- 
2.49.0