printk: avoid -Wsometimes-uninitialized warning

clang notices that the pi_get_entry() function would use
uninitialized data if it was called with a non-NULL module
pointer on a kernel that does not support modules:

kernel/printk/index.c:32:6: error: variable 'nr_entries' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
        if (!mod) {
            ^~~~
kernel/printk/index.c:38:13: note: uninitialized use occurs here
        if (pos >= nr_entries)
                   ^~~~~~~~~~
kernel/printk/index.c:32:2: note: remove the 'if' if its condition is always true
        if (!mod) {

Rework the condition to make it clear to the compiler that we are always
in the second case. Unfortunately the #ifdef is still required as the
definition of 'struct module' is hidden when modules are disabled.

Fixes: 337015573718 ("printk: Userspace format indexing support")
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210928093456.2438109-1-arnd@kernel.org

diff --git a/kernel/printk/index.c b/kernel/printk/index.c
index d3709408debe9ce708d0125f749f09b4f2af589e..c85be186a7832c4431ea2fcffd2800a2b5215e3a 100644 (file)
--- a/kernel/printk/index.c
+++ b/kernel/printk/index.c
@@ -26,10 +26,9 @@ static struct pi_entry *pi_get_entry(const struct module *mod, loff_t pos)
        if (mod) {
                entries = mod->printk_index_start;
                nr_entries = mod->printk_index_size;
-       }
+       } else
 #endif
-
-       if (!mod) {
+       {
                /* vmlinux, comes from linker symbols */
                entries = __start_printk_index;
                nr_entries = __stop_printk_index - __start_printk_index;