linux-kernel - [PATCH v2 55/62] objtool: Disallow duplicate prefix symbols

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Message-ID: <23e6ec37b579514e13ca33f08c6f1eaba9958d6d.1746821544.git.jpoimboe@kernel.org>
Date: Fri,  9 May 2025 13:17:19 -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 55/62] objtool: Disallow duplicate prefix symbols

In preparation for adding objtool 'check' support for analyzing
livepatch modules, error out if a duplicate prefix symbol is attempted.

Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
 tools/objtool/check.c               | 12 +++++++++++-
 tools/objtool/elf.c                 |  9 +++++++++
 tools/objtool/include/objtool/elf.h |  3 +++
 3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 30a5eb725931..bc9bc37efa55 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -4271,6 +4271,7 @@ static int add_prefix_symbol(struct objtool_file *file, struct symbol *func)
 	for (prev = prev_insn_same_sec(file, insn);
 	     prev;
 	     prev = prev_insn_same_sec(file, prev)) {
+		struct symbol *sym_pfx;
 		u64 offset;
 
 		if (prev->type != INSN_NOP)
@@ -4284,7 +4285,12 @@ static int add_prefix_symbol(struct objtool_file *file, struct symbol *func)
 		if (offset < opts.prefix)
 			continue;
 
-		elf_create_prefix_symbol(file->elf, func, opts.prefix);
+		sym_pfx = elf_create_prefix_symbol(file->elf, func, opts.prefix);
+		if (!sym_pfx) {
+			WARN("duplicate prefix symbol for %s\n", func->name);
+			return -1;
+		}
+
 		break;
 	}
 
@@ -4320,6 +4326,10 @@ static int add_prefix_symbols(struct objtool_file *file)
 			if (!is_func_sym(func))
 				continue;
 
+			/*
+			 * Ignore this error on purpose, there are valid
+			 * reasons for this to fail.
+			 */
 			add_prefix_symbol(file, func);
 		}
 	}
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 645f7ac12869..de1d8554d979 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -946,11 +946,20 @@ elf_create_prefix_symbol(struct elf *elf, struct symbol *orig, size_t size)
 	size_t namelen = strlen(orig->name) + sizeof("__pfx_");
 	char name[SYM_NAME_LEN];
 	unsigned long offset;
+	struct symbol *sym;
 
 	snprintf(name, namelen, "__pfx_%s", orig->name);
 
+	sym = orig;
 	offset = orig->sym.st_value - size;
 
+	sec_for_each_sym_continue_reverse(orig->sec, sym) {
+		if (sym->offset < offset)
+			break;
+		if (sym->offset == offset && !strcmp(sym->name, name))
+			return NULL;
+	}
+
 	return elf_create_symbol(elf, name, orig->sec,
 				 GELF_ST_BIND(orig->sym.st_info),
 				 GELF_ST_TYPE(orig->sym.st_info),
diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index f62ac8081f27..1bf9c0a1112d 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -443,6 +443,9 @@ static inline void set_sym_next_reloc(struct reloc *reloc, struct reloc *next)
 #define sec_for_each_sym(sec, sym)					\
 	list_for_each_entry(sym, &sec->symbol_list, list)
 
+#define sec_for_each_sym_continue_reverse(sec, sym)			\
+	list_for_each_entry_continue_reverse(sym, &sec->symbol_list, list)
+
 #define sec_prev_sym(sym)						\
 	sym->sec && sym->list.prev != &sym->sec->symbol_list ?		\
 	list_prev_entry(sym, list) : NULL
-- 
2.49.0