objtool/klp: Avoid NULL pointer dereference when printing code symbol name

Fix a hypothetical NULL pointer defereference of the 'code_sym'
variable.  In theory this should never happen.

Reviewed-and-tested-by: Song Liu <song@kernel.org>
Link: https://patch.msgid.link/64116517bc93851a98fe366ea0a4d807f4c70aab.1770759954.git.jpoimboe@kernel.org
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index 9ff65b01882b86fc43952a36129a559b4d143c68..a3198a63c2f0d7339985bcf471911ffd6f4396c9 100644 (file)
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -1352,7 +1352,7 @@ static int validate_special_section_klp_reloc(struct elfs *e, struct symbol *sym
 {
        bool static_branch = !strcmp(sym->sec->name, "__jump_table");
        bool static_call   = !strcmp(sym->sec->name, ".static_call_sites");
-       struct symbol *code_sym = NULL;
+       const char *code_sym = NULL;
        unsigned long code_offset = 0;
        struct reloc *reloc;
        int ret = 0;
@@ -1372,7 +1372,7 @@ static int validate_special_section_klp_reloc(struct elfs *e, struct symbol *sym
 
                        /* Save code location which can be printed below */
                        if (reloc->sym->type == STT_FUNC && !code_sym) {
-                               code_sym = reloc->sym;
+                               code_sym = reloc->sym->name;
                                code_offset = reloc_addend(reloc);
                        }
 
@@ -1395,23 +1395,26 @@ static int validate_special_section_klp_reloc(struct elfs *e, struct symbol *sym
                if (!strcmp(sym_modname, "vmlinux"))
                        continue;
 
+               if (!code_sym)
+                       code_sym = "<unknown>";
+
                if (static_branch) {
                        if (strstarts(reloc->sym->name, "__tracepoint_")) {
                                WARN("%s: disabling unsupported tracepoint %s",
-                                    code_sym->name, reloc->sym->name + 13);
+                                    code_sym, reloc->sym->name + 13);
                                ret = 1;
                                continue;
                        }
 
                        if (strstr(reloc->sym->name, "__UNIQUE_ID_ddebug_")) {
                                WARN("%s: disabling unsupported pr_debug()",
-                                    code_sym->name);
+                                    code_sym);
                                ret = 1;
                                continue;
                        }
 
                        ERROR("%s+0x%lx: unsupported static branch key %s.  Use static_key_enabled() instead",
-                             code_sym->name, code_offset, reloc->sym->name);
+                             code_sym, code_offset, reloc->sym->name);
                        return -1;
                }
 
@@ -1422,7 +1425,7 @@ static int validate_special_section_klp_reloc(struct elfs *e, struct symbol *sym
                }
 
                ERROR("%s()+0x%lx: unsupported static call key %s.  Use KLP_STATIC_CALL() instead",
-                     code_sym->name, code_offset, reloc->sym->name);
+                     code_sym, code_offset, reloc->sym->name);
                return -1;
        }