8 files changed, 52 insertions, 7 deletions

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 7eba5b5723e9..8d11babf9aa5 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -117,7 +117,6 @@ config S390
         select HAVE_BPF_JIT if 64BIT && PACK_STACK
         select HAVE_CMPXCHG_DOUBLE
         select HAVE_CMPXCHG_LOCAL
-        select HAVE_C_RECORDMCOUNT
         select HAVE_DEBUG_KMEMLEAK
         select HAVE_DYNAMIC_FTRACE if 64BIT
         select HAVE_DYNAMIC_FTRACE_WITH_REGS if 64BIT
diff --git a/arch/s390/Makefile b/arch/s390/Makefile
index e742ec5de9a7..acb6859c6a95 100644
--- a/arch/s390/Makefile
+++ b/arch/s390/Makefile
@@ -87,6 +87,16 @@ ifeq ($(call cc-option-yn,-mwarn-dynamicstack),y)
 cflags-$(CONFIG_WARN_DYNAMIC_STACK) += -mwarn-dynamicstack
 endif
 
+ifdef CONFIG_FUNCTION_TRACER
+# make use of hotpatch feature if the compiler supports it
+cc_hotpatch     := -mhotpatch=0,3
+ifeq ($(call cc-option-yn,$(cc_hotpatch)),y)
+CC_FLAGS_FTRACE := $(cc_hotpatch)
+KBUILD_AFLAGS   += -DCC_USING_HOTPATCH
+KBUILD_CFLAGS   += -DCC_USING_HOTPATCH
+endif
+endif
+
 KBUILD_CFLAGS   += -mbackchain -msoft-float $(cflags-y)
 KBUILD_CFLAGS   += -pipe -fno-strength-reduce -Wno-sign-compare
 KBUILD_AFLAGS   += $(aflags-y)
diff --git a/arch/s390/include/asm/ftrace.h b/arch/s390/include/asm/ftrace.h
index abb618f1ead2..836c56290499 100644
--- a/arch/s390/include/asm/ftrace.h
+++ b/arch/s390/include/asm/ftrace.h
@@ -3,8 +3,12 @@
 
 #define ARCH_SUPPORTS_FTRACE_OPS 1
 
+#ifdef CC_USING_HOTPATCH
+#define MCOUNT_INSN_SIZE        6
+#else
 #define MCOUNT_INSN_SIZE        24
 #define MCOUNT_RETURN_FIXUP     18
+#endif
 
 #ifndef __ASSEMBLY__
 
@@ -37,18 +41,29 @@ struct ftrace_insn {
 static inline void ftrace_generate_nop_insn(struct ftrace_insn *insn)
 {
 #ifdef CONFIG_FUNCTION_TRACER
+#ifdef CC_USING_HOTPATCH
+        /* brcl 0,0 */
+        insn->opc = 0xc004;
+        insn->disp = 0;
+#else
         /* jg .+24 */
         insn->opc = 0xc0f4;
         insn->disp = MCOUNT_INSN_SIZE / 2;
 #endif
+#endif
 }
 
 static inline int is_ftrace_nop(struct ftrace_insn *insn)
 {
 #ifdef CONFIG_FUNCTION_TRACER
+#ifdef CC_USING_HOTPATCH
+        if (insn->disp == 0)
+                return 1;
+#else
         if (insn->disp == MCOUNT_INSN_SIZE / 2)
                 return 1;
 #endif
+#endif
         return 0;
 }
 
diff --git a/arch/s390/kernel/Makefile b/arch/s390/kernel/Makefile
index 204c43a4c245..31fab2676fe9 100644
--- a/arch/s390/kernel/Makefile
+++ b/arch/s390/kernel/Makefile
@@ -4,8 +4,8 @@
 
 ifdef CONFIG_FUNCTION_TRACER
 # Don't trace early setup code and tracing code
-CFLAGS_REMOVE_early.o = -pg
-CFLAGS_REMOVE_ftrace.o = -pg
+CFLAGS_REMOVE_early.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_ftrace.o = $(CC_FLAGS_FTRACE)
 endif
 
 #
diff --git a/arch/s390/kernel/ftrace.c b/arch/s390/kernel/ftrace.c
index 3dabcae40e04..82c19899574f 100644
--- a/arch/s390/kernel/ftrace.c
+++ b/arch/s390/kernel/ftrace.c
@@ -46,6 +46,13 @@
  *      lg      %r14,8(%r15)            # offset 18
  * The jg instruction branches to offset 24 to skip as many instructions
  * as possible.
+ * In case we use gcc's hotpatch feature the original and also the disabled
+ * function prologue contains only a single six byte instruction and looks
+ * like this:
+ * >    brcl    0,0                     # offset 0
+ * To enable ftrace the code gets patched like above and afterwards looks
+ * like this:
+ * >    brasl   %r0,ftrace_caller       # offset 0
  */
 
 unsigned long ftrace_plt;
@@ -64,9 +71,15 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
         if (probe_kernel_read(&old, (void *) rec->ip, sizeof(old)))
                 return -EFAULT;
         if (addr == MCOUNT_ADDR) {
-                /* Initial code replacement; we expect to see stg r14,8(r15) */
+                /* Initial code replacement */
+#ifdef CC_USING_HOTPATCH
+                /* We expect to see brcl 0,0 */
+                ftrace_generate_nop_insn(&orig);
+#else
+                /* We expect to see stg r14,8(r15) */
                 orig.opc = 0xe3e0;
                 orig.disp = 0xf0080024;
+#endif
                 ftrace_generate_nop_insn(&new);
         } else if (old.opc == BREAKPOINT_INSTRUCTION) {
                 /*
diff --git a/arch/s390/kernel/kprobes.c b/arch/s390/kernel/kprobes.c
index 1e4c710dfb92..f516edc1fbe3 100644
--- a/arch/s390/kernel/kprobes.c
+++ b/arch/s390/kernel/kprobes.c
@@ -69,7 +69,8 @@ static void copy_instruction(struct kprobe *p)
                 /*
                  * If kprobes patches the instruction that is morphed by
                  * ftrace make sure that kprobes always sees the branch
-                 * "jg .+24" that skips the mcount block
+                 * "jg .+24" that skips the mcount block or the "brcl 0,0"
+                 * in case of hotpatch.
                  */
                 ftrace_generate_nop_insn((struct ftrace_insn *)p->ainsn.insn);
                 p->ainsn.is_ftrace_insn = 1;
diff --git a/arch/s390/kernel/mcount.S b/arch/s390/kernel/mcount.S
index b6dfc5bfcb89..e499370fbccb 100644
--- a/arch/s390/kernel/mcount.S
+++ b/arch/s390/kernel/mcount.S
@@ -27,7 +27,9 @@ ENTRY(ftrace_caller)
         .globl  ftrace_regs_caller
         .set    ftrace_regs_caller,ftrace_caller
         lgr     %r1,%r15
+#ifndef CC_USING_HOTPATCH
         aghi    %r0,MCOUNT_RETURN_FIXUP
+#endif
         aghi    %r15,-STACK_FRAME_SIZE
         stg     %r1,__SF_BACKCHAIN(%r15)
         stg     %r1,(STACK_PTREGS_GPRS+15*8)(%r15)
diff --git a/scripts/recordmcount.pl b/scripts/recordmcount.pl
index 56ea99a12ab7..be39be0abefc 100755
--- a/scripts/recordmcount.pl
+++ b/scripts/recordmcount.pl
@@ -242,8 +242,13 @@ if ($arch eq "x86_64") {
     $cc .= " -m32";
 
 } elsif ($arch eq "s390" && $bits == 64) {
-    $mcount_regex = "^\\s*([0-9a-fA-F]+):\\s*R_390_(PC|PLT)32DBL\\s+_mcount\\+0x2\$";
-    $mcount_adjust = -14;
+    if ($cc =~ /-DCC_USING_HOTPATCH/) {
+        $mcount_regex = "^\\s*([0-9a-fA-F]+):\\s*c0 04 00 00 00 00\\s*brcl\\s*0,[0-9a-f]+ <([^\+]*)>\$";
+        $mcount_adjust = 0;
+    } else {
+        $mcount_regex = "^\\s*([0-9a-fA-F]+):\\s*R_390_(PC|PLT)32DBL\\s+_mcount\\+0x2\$";
+        $mcount_adjust = -14;
+    }
     $alignment = 8;
     $type = ".quad";
     $ld .= " -m elf64_s390";