linux-kernel - [PATCH v4 31/63] objtool: Mark prefix functions

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Message-ID: <c4e61dc8954c14e80cbed9800e0d7399ae4c7289.1758067943.git.jpoimboe@kernel.org>
Date: Wed, 17 Sep 2025 09:03:39 -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>,
	Dylan Hatch <dylanbhatch@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH v4 31/63] objtool: Mark prefix functions

In preparation for the objtool klp diff subcommand, introduce a flag to
identify __pfx_*() and __cfi_*() functions in advance so they don't need
to be manually identified every time a check is needed.

Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
 tools/objtool/check.c               | 5 +----
 tools/objtool/elf.c                 | 7 +++++++
 tools/objtool/include/objtool/elf.h | 6 ++++++
 3 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 57e3b0cde19f2..6f7ed34aea43e 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -3577,10 +3577,7 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
 
 		if (func && insn_func(insn) && func != insn_func(insn)->pfunc) {
 			/* Ignore KCFI type preambles, which always fall through */
-			if (!strncmp(func->name, "__cfi_", 6) ||
-			    !strncmp(func->name, "__pfx_", 6) ||
-			    !strncmp(func->name, "__pi___cfi_", 11) ||
-			    !strncmp(func->name, "__pi___pfx_", 11))
+			if (is_prefix_func(func))
 				return 0;
 
 			if (file->ignore_unreachables)
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 59568381486c9..775d017b1b79b 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -442,6 +442,13 @@ static void elf_add_symbol(struct elf *elf, struct symbol *sym)
 	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) &&
+	    (strstarts(sym->name, "__pfx_") ||
+	     strstarts(sym->name, "__cfi_") ||
+	     strstarts(sym->name, "__pi___pfx_") ||
+	     strstarts(sym->name, "__pi___cfi_")))
+		sym->prefix = 1;
+
 	if (is_func_sym(sym) && strstr(sym->name, ".cold"))
 		sym->cold = 1;
 	sym->pfunc = sym->cfunc = sym;
diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index dbadcc88a3b26..79edf82e76ddf 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -73,6 +73,7 @@ struct symbol {
 	u8 ignore	     : 1;
 	u8 nocfi             : 1;
 	u8 cold		     : 1;
+	u8 prefix	     : 1;
 	struct list_head pv_target;
 	struct reloc *relocs;
 	struct section *group_sec;
@@ -230,6 +231,11 @@ static inline bool is_local_sym(struct symbol *sym)
 	return sym->bind == STB_LOCAL;
 }
 
+static inline bool is_prefix_func(struct symbol *sym)
+{
+	return sym->prefix;
+}
+
 static inline bool is_reloc_sec(struct section *sec)
 {
 	return sec->sh.sh_type == SHT_RELA || sec->sh.sh_type == SHT_REL;
-- 
2.50.0