13 files changed, 214 insertions, 92 deletions

diff --git a/arch/s390/include/asm/ftrace.h b/arch/s390/include/asm/ftrace.h
index 3aef8afec336..785041f1dc77 100644
--- a/arch/s390/include/asm/ftrace.h
+++ b/arch/s390/include/asm/ftrace.h
@@ -1,25 +1,67 @@
 #ifndef _ASM_S390_FTRACE_H
 #define _ASM_S390_FTRACE_H
 
+#define ARCH_SUPPORTS_FTRACE_OPS 1
+
+#define MCOUNT_INSN_SIZE	24
+#define MCOUNT_RETURN_FIXUP	18
+
 #ifndef __ASSEMBLY__
 
-extern void _mcount(void);
+void _mcount(void);
+void ftrace_caller(void);
+
 extern char ftrace_graph_caller_end;
+extern unsigned long ftrace_plt;
 
 struct dyn_arch_ftrace { };
 
-#define MCOUNT_ADDR ((long)_mcount)
+#define MCOUNT_ADDR ((unsigned long)_mcount)
+#define FTRACE_ADDR ((unsigned long)ftrace_caller)
 
+#define KPROBE_ON_FTRACE_NOP	0
+#define KPROBE_ON_FTRACE_CALL	1
 
 static inline unsigned long ftrace_call_adjust(unsigned long addr)
 {
 	return addr;
 }
 
-#endif /* __ASSEMBLY__ */
+struct ftrace_insn {
+	u16 opc;
+	s32 disp;
+} __packed;
 
-#define MCOUNT_INSN_SIZE  18
+static inline void ftrace_generate_nop_insn(struct ftrace_insn *insn)
+{
+#ifdef CONFIG_FUNCTION_TRACER
+	/* jg .+24 */
+	insn->opc = 0xc0f4;
+	insn->disp = MCOUNT_INSN_SIZE / 2;
+#endif
+}
 
-#define ARCH_SUPPORTS_FTRACE_OPS 1
+static inline int is_ftrace_nop(struct ftrace_insn *insn)
+{
+#ifdef CONFIG_FUNCTION_TRACER
+	if (insn->disp == MCOUNT_INSN_SIZE / 2)
+		return 1;
+#endif
+	return 0;
+}
+
+static inline void ftrace_generate_call_insn(struct ftrace_insn *insn,
+					     unsigned long ip)
+{
+#ifdef CONFIG_FUNCTION_TRACER
+	unsigned long target;
 
+	/* brasl r0,ftrace_caller */
+	target = is_module_addr((void *) ip) ? ftrace_plt : FTRACE_ADDR;
+	insn->opc = 0xc005;
+	insn->disp = (target - ip) / 2;
+#endif
+}
+
+#endif /* __ASSEMBLY__ */
 #endif /* _ASM_S390_FTRACE_H */
diff --git a/arch/s390/include/asm/kprobes.h b/arch/s390/include/asm/kprobes.h
index 98629173ce3b..b47ad3b642cc 100644
--- a/arch/s390/include/asm/kprobes.h
+++ b/arch/s390/include/asm/kprobes.h
@@ -60,6 +60,7 @@ typedef u16 kprobe_opcode_t;
 struct arch_specific_insn {
 	/* copy of original instruction */
 	kprobe_opcode_t *insn;
+	unsigned int is_ftrace_insn : 1;
 };
 
 struct prev_kprobe {
diff --git a/arch/s390/include/asm/lowcore.h b/arch/s390/include/asm/lowcore.h
index 6cc51fe84410..34fbcac61133 100644
--- a/arch/s390/include/asm/lowcore.h
+++ b/arch/s390/include/asm/lowcore.h
@@ -147,7 +147,7 @@ struct _lowcore {
 	__u32	softirq_pending;		/* 0x02ec */
 	__u32	percpu_offset;			/* 0x02f0 */
 	__u32	machine_flags;			/* 0x02f4 */
-	__u32	ftrace_func;			/* 0x02f8 */
+	__u8	pad_0x02f8[0x02fc-0x02f8];	/* 0x02f8 */
 	__u32	spinlock_lockval;		/* 0x02fc */
 
 	__u8	pad_0x0300[0x0e00-0x0300];	/* 0x0300 */
@@ -297,7 +297,7 @@ struct _lowcore {
 	__u64	percpu_offset;			/* 0x0378 */
 	__u64	vdso_per_cpu_data;		/* 0x0380 */
 	__u64	machine_flags;			/* 0x0388 */
-	__u64	ftrace_func;			/* 0x0390 */
+	__u8	pad_0x0390[0x0398-0x0390];	/* 0x0390 */
 	__u64	gmap;				/* 0x0398 */
 	__u32	spinlock_lockval;		/* 0x03a0 */
 	__u8	pad_0x03a0[0x0400-0x03a4];	/* 0x03a4 */
diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index 00d460742e1e..5ef1a266936a 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -133,6 +133,18 @@ extern unsigned long MODULES_END;
 #define MODULES_LEN	(1UL << 31)
 #endif
 
+static inline int is_module_addr(void *addr)
+{
+#ifdef CONFIG_64BIT
+	BUILD_BUG_ON(MODULES_LEN > (1UL << 31));
+	if (addr < (void *)MODULES_VADDR)
+		return 0;
+	if (addr > (void *)MODULES_END)
+		return 0;
+#endif
+	return 1;
+}
+
 /*
  * A 31 bit pagetable entry of S390 has following format:
  *  |   PFRA          |    |  OS  |
diff --git a/arch/s390/kernel/asm-offsets.c b/arch/s390/kernel/asm-offsets.c
index ef279a136801..f3a78337ca86 100644
--- a/arch/s390/kernel/asm-offsets.c
+++ b/arch/s390/kernel/asm-offsets.c
@@ -156,7 +156,6 @@ int main(void)
 	DEFINE(__LC_INT_CLOCK, offsetof(struct _lowcore, int_clock));
 	DEFINE(__LC_MCCK_CLOCK, offsetof(struct _lowcore, mcck_clock));
 	DEFINE(__LC_MACHINE_FLAGS, offsetof(struct _lowcore, machine_flags));
-	DEFINE(__LC_FTRACE_FUNC, offsetof(struct _lowcore, ftrace_func));
 	DEFINE(__LC_DUMP_REIPL, offsetof(struct _lowcore, ipib));
 	BLANK();
 	DEFINE(__LC_CPU_TIMER_SAVE_AREA, offsetof(struct _lowcore, cpu_timer_save_area));
diff --git a/arch/s390/kernel/early.c b/arch/s390/kernel/early.c
index cef2879edff3..302ac1f7f8e7 100644
--- a/arch/s390/kernel/early.c
+++ b/arch/s390/kernel/early.c
@@ -12,7 +12,6 @@
 #include <linux/errno.h>
 #include <linux/string.h>
 #include <linux/ctype.h>
-#include <linux/ftrace.h>
 #include <linux/lockdep.h>
 #include <linux/module.h>
 #include <linux/pfn.h>
@@ -490,8 +489,5 @@ void __init startup_init(void)
 	detect_machine_facilities();
 	setup_topology();
 	sclp_early_detect();
-#ifdef CONFIG_DYNAMIC_FTRACE
-	S390_lowcore.ftrace_func = (unsigned long)ftrace_caller;
-#endif
 	lockdep_on();
 }
diff --git a/arch/s390/kernel/ftrace.c b/arch/s390/kernel/ftrace.c
index 51d14fe5eb9a..5744d25c1d33 100644
--- a/arch/s390/kernel/ftrace.c
+++ b/arch/s390/kernel/ftrace.c
@@ -7,6 +7,7 @@
  *		Martin Schwidefsky <schwidefsky@de.ibm.com>
  */
 
+#include <linux/moduleloader.h>
 #include <linux/hardirq.h>
 #include <linux/uaccess.h>
 #include <linux/ftrace.h>
@@ -15,60 +16,39 @@
 #include <linux/kprobes.h>
 #include <trace/syscall.h>
 #include <asm/asm-offsets.h>
+#include <asm/cacheflush.h>
 #include "entry.h"
 
-void mcount_replace_code(void);
-void ftrace_disable_code(void);
-void ftrace_enable_insn(void);
-
 /*
  * The mcount code looks like this:
  *	stg	%r14,8(%r15)		# offset 0
  *	larl	%r1,<&counter>		# offset 6
  *	brasl	%r14,_mcount		# offset 12
  *	lg	%r14,8(%r15)		# offset 18
- * Total length is 24 bytes. The complete mcount block initially gets replaced
- * by ftrace_make_nop. Subsequent calls to ftrace_make_call / ftrace_make_nop
- * only patch the jg/lg instruction within the block.
- * Note: we do not patch the first instruction to an unconditional branch,
- * since that would break kprobes/jprobes. It is easier to leave the larl
- * instruction in and only modify the second instruction.
+ * Total length is 24 bytes. Only the first instruction will be patched
+ * by ftrace_make_call / ftrace_make_nop.
  * The enabled ftrace code block looks like this:
- *	larl	%r0,.+24		# offset 0
- * >	lg	%r1,__LC_FTRACE_FUNC	# offset 6
- *	br	%r1			# offset 12
- *	brcl	0,0			# offset 14
- *	brc	0,0			# offset 20
+ * >	brasl	%r0,ftrace_caller	# offset 0
+ *	larl	%r1,<&counter>		# offset 6
+ *	brasl	%r14,_mcount		# offset 12
+ *	lg	%r14,8(%r15)		# offset 18
  * The ftrace function gets called with a non-standard C function call ABI
  * where r0 contains the return address. It is also expected that the called
  * function only clobbers r0 and r1, but restores r2-r15.
+ * For module code we can't directly jump to ftrace caller, but need a
+ * trampoline (ftrace_plt), which clobbers also r1.
  * The return point of the ftrace function has offset 24, so execution
  * continues behind the mcount block.
- *	larl	%r0,.+24		# offset 0
- * >	jg	.+18			# offset 6
- *	br	%r1			# offset 12
- *	brcl	0,0			# offset 14
- *	brc	0,0			# offset 20
+ * The disabled ftrace code block looks like this:
+ * >	jg	.+24			# offset 0
+ *	larl	%r1,<&counter>		# offset 6
+ *	brasl	%r14,_mcount		# offset 12
+ *	lg	%r14,8(%r15)		# offset 18
  * The jg instruction branches to offset 24 to skip as many instructions
  * as possible.
  */
-asm(
-	"	.align	4\n"
-	"mcount_replace_code:\n"
-	"	larl	%r0,0f\n"
-	"ftrace_disable_code:\n"
-	"	jg	0f\n"
-	"	br	%r1\n"
-	"	brcl	0,0\n"
-	"	brc	0,0\n"
-	"0:\n"
-	"	.align	4\n"
-	"ftrace_enable_insn:\n"
-	"	lg	%r1,"__stringify(__LC_FTRACE_FUNC)"\n");
-
-#define MCOUNT_BLOCK_SIZE	24
-#define MCOUNT_INSN_OFFSET	6
-#define FTRACE_INSN_SIZE	6
+
+unsigned long ftrace_plt;
 
 int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
 		       unsigned long addr)
@@ -79,24 +59,62 @@ int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
 		    unsigned long addr)
 {
-	/* Initial replacement of the whole mcount block */
-	if (addr == MCOUNT_ADDR) {
-		if (probe_kernel_write((void *) rec->ip - MCOUNT_INSN_OFFSET,
-				       mcount_replace_code,
-				       MCOUNT_BLOCK_SIZE))
-			return -EPERM;
-		return 0;
+	struct ftrace_insn insn;
+	unsigned short op;
+	void *from, *to;
+	size_t size;
+
+	ftrace_generate_nop_insn(&insn);
+	size = sizeof(insn);
+	from = &insn;
+	to = (void *) rec->ip;
+	if (probe_kernel_read(&op, (void *) rec->ip, sizeof(op)))
+		return -EFAULT;
+	/*
+	 * If we find a breakpoint instruction, a kprobe has been placed
+	 * at the beginning of the function. We write the constant
+	 * KPROBE_ON_FTRACE_NOP into the remaining four bytes of the original
+	 * instruction so that the kprobes handler can execute a nop, if it
+	 * reaches this breakpoint.
+	 */
+	if (op == BREAKPOINT_INSTRUCTION) {
+		size -= 2;
+		from += 2;
+		to += 2;
+		insn.disp = KPROBE_ON_FTRACE_NOP;
 	}
-	if (probe_kernel_write((void *) rec->ip, ftrace_disable_code,
-			       MCOUNT_INSN_SIZE))
+	if (probe_kernel_write(to, from, size))
 		return -EPERM;
 	return 0;
 }
 
 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 {
-	if (probe_kernel_write((void *) rec->ip, ftrace_enable_insn,
-			       FTRACE_INSN_SIZE))
+	struct ftrace_insn insn;
+	unsigned short op;
+	void *from, *to;
+	size_t size;
+
+	ftrace_generate_call_insn(&insn, rec->ip);
+	size = sizeof(insn);
+	from = &insn;
+	to = (void *) rec->ip;
+	if (probe_kernel_read(&op, (void *) rec->ip, sizeof(op)))
+		return -EFAULT;
+	/*
+	 * If we find a breakpoint instruction, a kprobe has been placed
+	 * at the beginning of the function. We write the constant
+	 * KPROBE_ON_FTRACE_CALL into the remaining four bytes of the original
+	 * instruction so that the kprobes handler can execute a brasl if it
+	 * reaches this breakpoint.
+	 */
+	if (op == BREAKPOINT_INSTRUCTION) {
+		size -= 2;
+		from += 2;
+		to += 2;
+		insn.disp = KPROBE_ON_FTRACE_CALL;
+	}
+	if (probe_kernel_write(to, from, size))
 		return -EPERM;
 	return 0;
 }
@@ -111,6 +129,24 @@ int __init ftrace_dyn_arch_init(void)
 	return 0;
 }
 
+static int __init ftrace_plt_init(void)
+{
+	unsigned int *ip;
+
+	ftrace_plt = (unsigned long) module_alloc(PAGE_SIZE);
+	if (!ftrace_plt)
+		panic("cannot allocate ftrace plt\n");
+	ip = (unsigned int *) ftrace_plt;
+	ip[0] = 0x0d10e310; /* basr 1,0; lg 1,10(1); br 1 */
+	ip[1] = 0x100a0004;
+	ip[2] = 0x07f10000;
+	ip[3] = FTRACE_ADDR >> 32;
+	ip[4] = FTRACE_ADDR & 0xffffffff;
+	set_memory_ro(ftrace_plt, 1);
+	return 0;
+}
+device_initcall(ftrace_plt_init);
+
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 /*
  * Hook the return address and push it in the stack of return addresses
diff --git a/arch/s390/kernel/kprobes.c b/arch/s390/kernel/kprobes.c
index 014d4729b134..d6716c29b7f8 100644
--- a/arch/s390/kernel/kprobes.c
+++ b/arch/s390/kernel/kprobes.c
@@ -29,6 +29,7 @@
 #include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/hardirq.h>
+#include <linux/ftrace.h>
 #include <asm/cacheflush.h>
 #include <asm/sections.h>
 #include <asm/dis.h>
@@ -60,10 +61,21 @@ struct kprobe_insn_cache kprobe_dmainsn_slots = {
 
 static void __kprobes copy_instruction(struct kprobe *p)
 {
+	unsigned long ip = (unsigned long) p->addr;
 	s64 disp, new_disp;
 	u64 addr, new_addr;
 
-	memcpy(p->ainsn.insn, p->addr, insn_length(p->opcode >> 8));
+	if (ftrace_location(ip) == ip) {
+		/*
+		 * 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
+		 */
+		ftrace_generate_nop_insn((struct ftrace_insn *)p->ainsn.insn);
+		p->ainsn.is_ftrace_insn = 1;
+	} else
+		memcpy(p->ainsn.insn, p->addr, insn_length(p->opcode >> 8));
+	p->opcode = p->ainsn.insn[0];
 	if (!probe_is_insn_relative_long(p->ainsn.insn))
 		return;
 	/*
@@ -85,18 +97,6 @@ static inline int is_kernel_addr(void *addr)
 	return addr < (void *)_end;
 }
 
-static inline int is_module_addr(void *addr)
-{
-#ifdef CONFIG_64BIT
-	BUILD_BUG_ON(MODULES_LEN > (1UL << 31));
-	if (addr < (void *)MODULES_VADDR)
-		return 0;
-	if (addr > (void *)MODULES_END)
-		return 0;
-#endif
-	return 1;
-}
-
 static int __kprobes s390_get_insn_slot(struct kprobe *p)
 {
 	/*
@@ -132,43 +132,63 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
 		return -EINVAL;
 	if (s390_get_insn_slot(p))
 		return -ENOMEM;
-	p->opcode = *p->addr;
 	copy_instruction(p);
 	return 0;
 }
 
-struct ins_replace_args {
-	kprobe_opcode_t *ptr;
-	kprobe_opcode_t opcode;
+int arch_check_ftrace_location(struct kprobe *p)
+{
+	return 0;
+}
+
+struct swap_insn_args {
+	struct kprobe *p;
+	unsigned int arm_kprobe : 1;
 };
 
-static int __kprobes swap_instruction(void *aref)
+static int __kprobes swap_instruction(void *data)
 {
 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 	unsigned long status = kcb->kprobe_status;
-	struct ins_replace_args *args = aref;
-
+	struct swap_insn_args *args = data;
+	struct ftrace_insn new_insn, *insn;
+	struct kprobe *p = args->p;
+	size_t len;
+
+	new_insn.opc = args->arm_kprobe ? BREAKPOINT_INSTRUCTION : p->opcode;
+	len = sizeof(new_insn.opc);
+	if (!p->ainsn.is_ftrace_insn)
+		goto skip_ftrace;
+	len = sizeof(new_insn);
+	insn = (struct ftrace_insn *) p->addr;
+	if (args->arm_kprobe) {
+		if (is_ftrace_nop(insn))
+			new_insn.disp = KPROBE_ON_FTRACE_NOP;
+		else
+			new_insn.disp = KPROBE_ON_FTRACE_CALL;
+	} else {
+		ftrace_generate_call_insn(&new_insn, (unsigned long)p->addr);
+		if (insn->disp == KPROBE_ON_FTRACE_NOP)
+			ftrace_generate_nop_insn(&new_insn);
+	}
+skip_ftrace:
 	kcb->kprobe_status = KPROBE_SWAP_INST;
-	probe_kernel_write(args->ptr, &args->opcode, sizeof(args->opcode));
+	probe_kernel_write(p->addr, &new_insn, len);
 	kcb->kprobe_status = status;
 	return 0;
 }
 
 void __kprobes arch_arm_kprobe(struct kprobe *p)
 {
-	struct ins_replace_args args;
+	struct swap_insn_args args = {.p = p, .arm_kprobe = 1};
 
-	args.ptr = p->addr;
-	args.opcode = BREAKPOINT_INSTRUCTION;
 	stop_machine(swap_instruction, &args, NULL);
 }
 
 void __kprobes arch_disarm_kprobe(struct kprobe *p)
 {
-	struct ins_replace_args args;
+	struct swap_insn_args args = {.p = p, .arm_kprobe = 0};
 
-	args.ptr = p->addr;
-	args.opcode = p->opcode;
 	stop_machine(swap_instruction, &args, NULL);
 }
 
@@ -459,6 +479,24 @@ static void __kprobes resume_execution(struct kprobe *p, struct pt_regs *regs)
 	unsigned long ip = regs->psw.addr & PSW_ADDR_INSN;
 	int fixup = probe_get_fixup_type(p->ainsn.insn);
 
+	/* Check if the kprobes location is an enabled ftrace caller */
+	if (p->ainsn.is_ftrace_insn) {
+		struct ftrace_insn *insn = (struct ftrace_insn *) p->addr;
+		struct ftrace_insn call_insn;
+
+		ftrace_generate_call_insn(&call_insn, (unsigned long) p->addr);
+		/*
+		 * A kprobe on an enabled ftrace call site actually single
+		 * stepped an unconditional branch (ftrace nop equivalent).
+		 * Now we need to fixup things and pretend that a brasl r0,...
+		 * was executed instead.
+		 */
+		if (insn->disp == KPROBE_ON_FTRACE_CALL) {
+			ip += call_insn.disp * 2 - MCOUNT_INSN_SIZE;
+			regs->gprs[0] = (unsigned long)p->addr + sizeof(*insn);
+		}
+	}
+
 	if (fixup & FIXUP_PSW_NORMAL)
 		ip += (unsigned long) p->addr - (unsigned long) p->ainsn.insn;
 
diff --git a/arch/s390/kernel/mcount.S b/arch/s390/kernel/mcount.S
index 4300ea374826..b6dfc5bfcb89 100644
--- a/arch/s390/kernel/mcount.S
+++ b/arch/s390/kernel/mcount.S
@@ -27,6 +27,7 @@ ENTRY(ftrace_caller)
 	.globl	ftrace_regs_caller
 	.set	ftrace_regs_caller,ftrace_caller
 	lgr	%r1,%r15
+	aghi	%r0,MCOUNT_RETURN_FIXUP
 	aghi	%r15,-STACK_FRAME_SIZE
 	stg	%r1,__SF_BACKCHAIN(%r15)
 	stg	%r1,(STACK_PTREGS_GPRS+15*8)(%r15)
diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c
index e80d9ff9a56d..4e532c67832f 100644
--- a/arch/s390/kernel/setup.c
+++ b/arch/s390/kernel/setup.c
@@ -41,7 +41,6 @@
 #include <linux/ctype.h>
 #include <linux/reboot.h>
 #include <linux/topology.h>
-#include <linux/ftrace.h>
 #include <linux/kexec.h>
 #include <linux/crash_dump.h>
 #include <linux/memory.h>
@@ -356,7 +355,6 @@ static void __init setup_lowcore(void)
 	lc->steal_timer = S390_lowcore.steal_timer;
 	lc->last_update_timer = S390_lowcore.last_update_timer;
 	lc->last_update_clock = S390_lowcore.last_update_clock;
-	lc->ftrace_func = S390_lowcore.ftrace_func;
 
 	restart_stack = __alloc_bootmem(ASYNC_SIZE, ASYNC_SIZE, 0);
 	restart_stack += ASYNC_SIZE;
diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
index 6fd9e60101f1..0b499f5cbe19 100644
--- a/arch/s390/kernel/smp.c
+++ b/arch/s390/kernel/smp.c
@@ -236,7 +236,6 @@ static void pcpu_prepare_secondary(struct pcpu *pcpu, int cpu)
 	lc->percpu_offset = __per_cpu_offset[cpu];
 	lc->kernel_asce = S390_lowcore.kernel_asce;
 	lc->machine_flags = S390_lowcore.machine_flags;
-	lc->ftrace_func = S390_lowcore.ftrace_func;
 	lc->user_timer = lc->system_timer = lc->steal_timer = 0;
 	__ctl_store(lc->cregs_save_area, 0, 15);
 	save_access_regs((unsigned int *) lc->access_regs_save_area);
diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c
index 001facfa5b74..3d1984e59a30 100644
--- a/scripts/recordmcount.c
+++ b/scripts/recordmcount.c
@@ -404,7 +404,7 @@ do_file(char const *const fname)
 		}
 		if (w2(ghdr->e_machine) == EM_S390) {
 			reltype = R_390_64;
-			mcount_adjust_64 = -8;
+			mcount_adjust_64 = -14;
 		}
 		if (w2(ghdr->e_machine) == EM_MIPS) {
 			reltype = R_MIPS_64;
diff --git a/scripts/recordmcount.pl b/scripts/recordmcount.pl
index d4b665610d67..56ea99a12ab7 100755
--- a/scripts/recordmcount.pl
+++ b/scripts/recordmcount.pl
@@ -243,7 +243,7 @@ if ($arch eq "x86_64") {
 
 } elsif ($arch eq "s390" && $bits == 64) {
     $mcount_regex = "^\\s*([0-9a-fA-F]+):\\s*R_390_(PC|PLT)32DBL\\s+_mcount\\+0x2\$";
-    $mcount_adjust = -8;
+    $mcount_adjust = -14;
     $alignment = 8;
     $type = ".quad";
     $ld .= " -m elf64_s390";