perf symbols: Fix use-after-free in get_plt_got_name()

Fix use-after-free in get_plt_got_name().

Discovered using EXTRA_CFLAGS="-fsanitize=undefined -fsanitize=address".

Fixes: ce4c8e79 ("perf symbols: Get symbols for .plt.got for x86-64")
Reported-by: kernel test robot <yujie.liu@intel.com>
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/oe-lkp/202303061424.6ad43294-yujie.liu@intel.com
Link: https://lore.kernel.org/r/20230316194156.8320-2-adrian.hunter@intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/symbol-elf.c

@@ -557,6 +557,7 @@ static bool get_plt_got_name(GElf_Shdr *shdr, size_t i,
 	const char *sym_name;
 	char *demangled;
 	GElf_Sym sym;
+	bool result;
 	u32 disp;
 
 	if (!di->sorted)
@@ -583,9 +584,11 @@ static bool get_plt_got_name(GElf_Shdr *shdr, size_t i,
 
 	snprintf(buf, buf_sz, "%s@plt", sym_name);
 
+	result = *sym_name;
+
 	free(demangled);
 
-	return *sym_name;
+	return result;
 }
 
 static int dso__synthesize_plt_got_symbols(struct dso *dso, Elf *elf,