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 <[email protected]> Signed-off-by: Jiri Kosina <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Acked-by: Josh Poimboeuf <[email protected]>
opendata26 · Jan 9, 2015 · b9dfe0b · b9dfe0b
1 parent 83ac237
commit b9dfe0b
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diff --git a/arch/x86/include/asm/livepatch.h b/arch/x86/include/asm/livepatch.h
@@ -25,9 +25,13 @@
 #include <linux/ftrace.h>
 
 #ifdef CONFIG_LIVE_PATCHING
+static inline int klp_check_compiler_support(void)
+{
 #ifndef CC_USING_FENTRY
-#error Your compiler must support -mfentry for live patching to work
+	return 1;
 #endif
+	return 0;
+}
 extern int klp_write_module_reloc(struct module *mod, unsigned long type,
 				  unsigned long loc, unsigned long value);
 

diff --git 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;