From 56e33afd7757d5da2664fb797f2544ce167176be Mon Sep 17 00:00:00 2001
From: Jiri Kosina <jkosina@suse.cz>
Date: Fri, 10 May 2019 23:47:50 +0200
Subject: [PATCH] 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/nycvar.YFH.7.76.1905102346100.17054@cbobk.fhfr.pm

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 arch/powerpc/include/asm/livepatch.h | 5 -----
 arch/s390/include/asm/livepatch.h    | 5 -----
 arch/x86/include/asm/livepatch.h     | 5 -----
 kernel/livepatch/core.c              | 8 --------
 4 files changed, 23 deletions(-)

diff --git a/arch/powerpc/include/asm/livepatch.h b/arch/powerpc/include/asm/livepatch.h
index 5070df19d463..c005aee5ea43 100644
--- a/arch/powerpc/include/asm/livepatch.h
+++ b/arch/powerpc/include/asm/livepatch.h
@@ -24,11 +24,6 @@
 #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;
diff --git a/arch/s390/include/asm/livepatch.h b/arch/s390/include/asm/livepatch.h
index 672f95b12d40..818612b784cd 100644
--- a/arch/s390/include/asm/livepatch.h
+++ b/arch/s390/include/asm/livepatch.h
@@ -13,11 +13,6 @@
 
 #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;
diff --git a/arch/x86/include/asm/livepatch.h b/arch/x86/include/asm/livepatch.h
index 2f2bdf0662f8..a66f6706c2de 100644
--- a/arch/x86/include/asm/livepatch.h
+++ b/arch/x86/include/asm/livepatch.h
@@ -24,11 +24,6 @@
 #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;
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index eb0ee10a1981..112a36ed4a09 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -1220,14 +1220,6 @@ void klp_module_going(struct module *mod)
 
 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;