livepatch: Remove klp_check_compiler_support()

The only purpose of klp_check_compiler_support() is to make sure that we
are not using ftrace on x86 via mcount (because that's executed only after
prologue has already happened, and that's too late for livepatching
purposes).

Now that mcount is not supported by ftrace any more, there is no need for
klp_check_compiler_support() either.

Link: http://lkml.kernel.org/r/[e-mail]

Reported-by: Linus Torvalds <[e-mail]>
Signed-off-by: Jiri Kosina <[e-mail]>
Signed-off-by: Steven Rostedt (VMware) <[e-mail]>

arch/powerpc/include/asm/livepatch.h

···
 #include <linux/sched/task_stack.h>
 
 #ifdef CONFIG_LIVEPATCH
-static inline int klp_check_compiler_support(void)
-{
-	return 0;
-}
-
 static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
 {
 	regs->nip = ip;

arch/s390/include/asm/livepatch.h

···
 
 #include <asm/ptrace.h>
 
-static inline int klp_check_compiler_support(void)
-{
-	return 0;
-}
-
 static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
 {
 	regs->psw.addr = ip;

arch/x86/include/asm/livepatch.h

···
 #include <asm/setup.h>
 #include <linux/ftrace.h>
 
-static inline int klp_check_compiler_support(void)
-{
-	return 0;
-}
-
 static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
 {
 	regs->ip = ip;

kernel/livepatch/core.c

···
 
 static int __init klp_init(void)
 {
-	int ret;
-
-	ret = klp_check_compiler_support();
-	if (ret) {
-		pr_info("Your compiler is too old; turning off.\n");
-		return -EINVAL;
-	}
-
 	klp_root_kobj = kobject_create_and_add("livepatch", kernel_kobj);
 	if (!klp_root_kobj)
 		return -ENOMEM;