livepatch: handle ancient compilers with more grace

We are aborting a build in case when gcc doesn't support fentry on x86_64
(regs->ip modification can't really reliably work with mcount).

This however breaks allmodconfig for people with older gccs that don't
support -mfentry.

Turn the build-time failure into runtime failure, resulting in the whole
infrastructure not being initialized if CC_USING_FENTRY is unset.

Reported-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 6f6387912da7..ce42d3b930dc 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -911,6 +911,12 @@ static int klp_init(void)
 {
         int ret;
 
+        ret = klp_check_compiler_support();
+        if (ret) {
+                pr_info("Your compiler is too old; turning off.\n");
+                return -EINVAL;
+        }
+
         ret = register_module_notifier(&klp_module_nb);
         if (ret)
                 return ret;