linux-kernel - [PATCH 2/2] objtool: use strndup() to avoid the need for a maximum symbol name length

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Date:   Wed, 4 Oct 2023 17:08:19 -0700
From:   Aaron Plattner <aplattner@...dia.com>
To:     <linux-kernel@...r.kernel.org>
CC:     Josh Poimboeuf <jpoimboe@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Aaron Plattner <aplattner@...dia.com>
Subject: [PATCH 2/2] objtool: use strndup() to avoid the need for a maximum symbol name length

If one of the symbols processed by read_symbols() happens to have a .cold
variant with a name longer than objtool's MAX_NAME_LEN limit, the build
fails.

Avoid this problem by just using strndup() to copy the parent function's
name, rather than strncpy()ing it onto the stack.

Signed-off-by: Aaron Plattner <aplattner@...dia.com>
Cc: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
---
 tools/objtool/elf.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 081befa4674b8..3d27983dc908d 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -22,8 +22,6 @@
 #include <objtool/elf.h>
 #include <objtool/warn.h>
 
-#define MAX_NAME_LEN 128
-
 static inline u32 str_hash(const char *str)
 {
 	return jhash(str, strlen(str), 0);
@@ -515,7 +513,7 @@ static int read_symbols(struct elf *elf)
 	/* Create parent/child links for any cold subfunctions */
 	list_for_each_entry(sec, &elf->sections, list) {
 		sec_for_each_sym(sec, sym) {
-			char pname[MAX_NAME_LEN + 1];
+			char *pname;
 			size_t pnamelen;
 			if (sym->type != STT_FUNC)
 				continue;
@@ -531,15 +529,15 @@ static int read_symbols(struct elf *elf)
 				continue;
 
 			pnamelen = coldstr - sym->name;
-			if (pnamelen > MAX_NAME_LEN) {
-				WARN("%s(): parent function name exceeds maximum length of %d characters",
-				     sym->name, MAX_NAME_LEN);
+			pname = strndup(sym->name, pnamelen);
+			if (!pname) {
+				WARN("%s(): failed to allocate memory",
+				     sym->name);
 				return -1;
 			}
 
-			strncpy(pname, sym->name, pnamelen);
-			pname[pnamelen] = '\0';
 			pfunc = find_symbol_by_name(elf, pname);
+			free(pname);
 
 			if (!pfunc) {
 				WARN("%s(): can't find parent function",
-- 
2.42.0