objtool: Remove max symbol name length limitation

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@nvidia.com>
Link: https://lore.kernel.org/r/41e94cfea1d9131b758dd637fecdeacd459d4584.1696355111.git.aplattner@nvidia.com
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Author: aaronp24

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",