s390/unwind: introduce stack unwind API

Rework the dump_trace() stack unwinder interface to support different
unwinding algorithms. The new interface looks like this:

	struct unwind_state state;
	unwind_for_each_frame(&state, task, regs, start_stack)
		do_something(state.sp, state.ip, state.reliable);

The unwind_bc.c file contains the implementation for the classic
back-chain unwinder.

One positive side effect of the new code is it now handles ftraced
functions gracefully. It prints the real name of the return function
instead of 'return_to_handler'.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/processor.h

@@ -156,25 +156,6 @@ struct thread_struct {
 
 typedef struct thread_struct thread_struct;
 
-/*
- * Stack layout of a C stack frame.
- */
-#ifndef __PACK_STACK
-struct stack_frame {
-	unsigned long back_chain;
-	unsigned long empty1[5];
-	unsigned long gprs[10];
-	unsigned int  empty2[8];
-};
-#else
-struct stack_frame {
-	unsigned long empty1[5];
-	unsigned int  empty2[8];
-	unsigned long gprs[10];
-	unsigned long back_chain;
-};
-#endif
-
 #define ARCH_MIN_TASKALIGN	8
 
 #define INIT_THREAD {							\
@@ -206,11 +187,7 @@ struct mm_struct;
 struct seq_file;
 struct pt_regs;
 
-typedef int (*dump_trace_func_t)(void *data, unsigned long address, int reliable);
-void dump_trace(dump_trace_func_t func, void *data,
-		struct task_struct *task, unsigned long sp);
 void show_registers(struct pt_regs *regs);
-
 void show_cacheinfo(struct seq_file *m);
 
 /* Free all resources held by a thread. */
@@ -244,55 +221,6 @@ static __no_kasan_or_inline unsigned short stap(void)
 	return cpu_address;
 }
 
-#define CALL_ARGS_0()							\
-	register unsigned long r2 asm("2")
-#define CALL_ARGS_1(arg1)						\
-	register unsigned long r2 asm("2") = (unsigned long)(arg1)
-#define CALL_ARGS_2(arg1, arg2)						\
-	CALL_ARGS_1(arg1);						\
-	register unsigned long r3 asm("3") = (unsigned long)(arg2)
-#define CALL_ARGS_3(arg1, arg2, arg3)					\
-	CALL_ARGS_2(arg1, arg2);					\
-	register unsigned long r4 asm("4") = (unsigned long)(arg3)
-#define CALL_ARGS_4(arg1, arg2, arg3, arg4)				\
-	CALL_ARGS_3(arg1, arg2, arg3);					\
-	register unsigned long r4 asm("5") = (unsigned long)(arg4)
-#define CALL_ARGS_5(arg1, arg2, arg3, arg4, arg5)			\
-	CALL_ARGS_4(arg1, arg2, arg3, arg4);				\
-	register unsigned long r4 asm("6") = (unsigned long)(arg5)
-
-#define CALL_FMT_0 "=&d" (r2) :
-#define CALL_FMT_1 "+&d" (r2) :
-#define CALL_FMT_2 CALL_FMT_1 "d" (r3),
-#define CALL_FMT_3 CALL_FMT_2 "d" (r4),
-#define CALL_FMT_4 CALL_FMT_3 "d" (r5),
-#define CALL_FMT_5 CALL_FMT_4 "d" (r6),
-
-#define CALL_CLOBBER_5 "0", "1", "14", "cc", "memory"
-#define CALL_CLOBBER_4 CALL_CLOBBER_5
-#define CALL_CLOBBER_3 CALL_CLOBBER_4, "5"
-#define CALL_CLOBBER_2 CALL_CLOBBER_3, "4"
-#define CALL_CLOBBER_1 CALL_CLOBBER_2, "3"
-#define CALL_CLOBBER_0 CALL_CLOBBER_1
-
-#define CALL_ON_STACK(fn, stack, nr, args...)				\
-({									\
-	CALL_ARGS_##nr(args);						\
-	unsigned long prev;						\
-									\
-	asm volatile(							\
-		"	la	%[_prev],0(15)\n"			\
-		"	la	15,0(%[_stack])\n"			\
-		"	stg	%[_prev],%[_bc](15)\n"			\
-		"	brasl	14,%[_fn]\n"				\
-		"	la	15,0(%[_prev])\n"			\
-		: [_prev] "=&a" (prev), CALL_FMT_##nr			\
-		  [_stack] "a" (stack),					\
-		  [_bc] "i" (offsetof(struct stack_frame, back_chain)),	\
-		  [_fn] "X" (fn) : CALL_CLOBBER_##nr);			\
-	r2;								\
-})
-
 /*
  * Give up the time slice of the virtual PU.
  */

arch/s390/include/asm/stacktrace.h

@@ -0,0 +1,114 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_S390_STACKTRACE_H
+#define _ASM_S390_STACKTRACE_H
+
+#include <linux/uaccess.h>
+#include <linux/ptrace.h>
+#include <asm/switch_to.h>
+
+enum stack_type {
+	STACK_TYPE_UNKNOWN,
+	STACK_TYPE_TASK,
+	STACK_TYPE_IRQ,
+	STACK_TYPE_NODAT,
+	STACK_TYPE_RESTART,
+};
+
+struct stack_info {
+	enum stack_type type;
+	unsigned long begin, end;
+};
+
+const char *stack_type_name(enum stack_type type);
+int get_stack_info(unsigned long sp, struct task_struct *task,
+		   struct stack_info *info, unsigned long *visit_mask);
+
+static inline bool on_stack(struct stack_info *info,
+			    unsigned long addr, size_t len)
+{
+	if (info->type == STACK_TYPE_UNKNOWN)
+		return false;
+	if (addr + len < addr)
+		return false;
+	return addr >= info->begin && addr + len < info->end;
+}
+
+static inline unsigned long get_stack_pointer(struct task_struct *task,
+					      struct pt_regs *regs)
+{
+	if (regs)
+		return (unsigned long) kernel_stack_pointer(regs);
+	if (task == current)
+		return current_stack_pointer();
+	return (unsigned long) task->thread.ksp;
+}
+
+/*
+ * Stack layout of a C stack frame.
+ */
+#ifndef __PACK_STACK
+struct stack_frame {
+	unsigned long back_chain;
+	unsigned long empty1[5];
+	unsigned long gprs[10];
+	unsigned int  empty2[8];
+};
+#else
+struct stack_frame {
+	unsigned long empty1[5];
+	unsigned int  empty2[8];
+	unsigned long gprs[10];
+	unsigned long back_chain;
+};
+#endif
+
+#define CALL_ARGS_0()							\
+	register unsigned long r2 asm("2")
+#define CALL_ARGS_1(arg1)						\
+	register unsigned long r2 asm("2") = (unsigned long)(arg1)
+#define CALL_ARGS_2(arg1, arg2)						\
+	CALL_ARGS_1(arg1);						\
+	register unsigned long r3 asm("3") = (unsigned long)(arg2)
+#define CALL_ARGS_3(arg1, arg2, arg3)					\
+	CALL_ARGS_2(arg1, arg2);					\
+	register unsigned long r4 asm("4") = (unsigned long)(arg3)
+#define CALL_ARGS_4(arg1, arg2, arg3, arg4)				\
+	CALL_ARGS_3(arg1, arg2, arg3);					\
+	register unsigned long r4 asm("5") = (unsigned long)(arg4)
+#define CALL_ARGS_5(arg1, arg2, arg3, arg4, arg5)			\
+	CALL_ARGS_4(arg1, arg2, arg3, arg4);				\
+	register unsigned long r4 asm("6") = (unsigned long)(arg5)
+
+#define CALL_FMT_0 "=&d" (r2) :
+#define CALL_FMT_1 "+&d" (r2) :
+#define CALL_FMT_2 CALL_FMT_1 "d" (r3),
+#define CALL_FMT_3 CALL_FMT_2 "d" (r4),
+#define CALL_FMT_4 CALL_FMT_3 "d" (r5),
+#define CALL_FMT_5 CALL_FMT_4 "d" (r6),
+
+#define CALL_CLOBBER_5 "0", "1", "14", "cc", "memory"
+#define CALL_CLOBBER_4 CALL_CLOBBER_5
+#define CALL_CLOBBER_3 CALL_CLOBBER_4, "5"
+#define CALL_CLOBBER_2 CALL_CLOBBER_3, "4"
+#define CALL_CLOBBER_1 CALL_CLOBBER_2, "3"
+#define CALL_CLOBBER_0 CALL_CLOBBER_1
+
+#define CALL_ON_STACK(fn, stack, nr, args...)				\
+({									\
+	CALL_ARGS_##nr(args);						\
+	unsigned long prev;						\
+									\
+	asm volatile(							\
+		"	la	%[_prev],0(15)\n"			\
+		"	la	15,0(%[_stack])\n"			\
+		"	stg	%[_prev],%[_bc](15)\n"			\
+		"	brasl	14,%[_fn]\n"				\
+		"	la	15,0(%[_prev])\n"			\
+		: [_prev] "=&a" (prev), CALL_FMT_##nr			\
+		  [_stack] "a" (stack),					\
+		  [_bc] "i" (offsetof(struct stack_frame, back_chain)),	\
+		  [_fn] "X" (fn) : CALL_CLOBBER_##nr);			\
+	r2;								\
+})
+
+#endif /* _ASM_S390_STACKTRACE_H */

arch/s390/include/asm/unwind.h

@@ -0,0 +1,101 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_S390_UNWIND_H
+#define _ASM_S390_UNWIND_H
+
+#include <linux/sched.h>
+#include <linux/ftrace.h>
+#include <asm/ptrace.h>
+#include <asm/stacktrace.h>
+
+/*
+ * To use the stack unwinder it has to be initialized with unwind_start.
+ * There four combinations for task and regs:
+ * 1) task==NULL, regs==NULL: the unwind starts for the task that is currently
+ *    running, sp/ip picked up from the CPU registers
+ * 2) task==NULL, regs!=NULL: the unwind starts from the sp/ip found in
+ *    the struct pt_regs of an interrupt frame for the current task
+ * 3) task!=NULL, regs==NULL: the unwind starts for an inactive task with
+ *    the sp picked up from task->thread.ksp and the ip picked up from the
+ *    return address stored by __switch_to
+ * 4) task!=NULL, regs!=NULL: the sp/ip are picked up from the interrupt
+ *    frame 'regs' of a inactive task
+ * If 'first_frame' is not zero unwind_start skips unwind frames until it
+ * reaches the specified stack pointer.
+ * The end of the unwinding is indicated with unwind_done, this can be true
+ * right after unwind_start, e.g. with first_frame!=0 that can not be found.
+ * unwind_next_frame skips to the next frame.
+ * Once the unwind is completed unwind_error() can be used to check if there
+ * has been a situation where the unwinder could not correctly understand
+ * the tasks call chain.
+ */
+
+struct unwind_state {
+	struct stack_info stack_info;
+	unsigned long stack_mask;
+	struct task_struct *task;
+	struct pt_regs *regs;
+	unsigned long sp, ip;
+	int graph_idx;
+	bool reliable;
+	bool error;
+};
+
+void __unwind_start(struct unwind_state *state, struct task_struct *task,
+		    struct pt_regs *regs, unsigned long first_frame);
+bool unwind_next_frame(struct unwind_state *state);
+unsigned long unwind_get_return_address(struct unwind_state *state);
+
+static inline bool unwind_done(struct unwind_state *state)
+{
+	return state->stack_info.type == STACK_TYPE_UNKNOWN;
+}
+
+static inline bool unwind_error(struct unwind_state *state)
+{
+	return state->error;
+}
+
+static inline void unwind_start(struct unwind_state *state,
+				struct task_struct *task,
+				struct pt_regs *regs,
+				unsigned long sp)
+{
+	sp = sp ? : get_stack_pointer(task, regs);
+	__unwind_start(state, task, regs, sp);
+}
+
+static inline struct pt_regs *unwind_get_entry_regs(struct unwind_state *state)
+{
+	return unwind_done(state) ? NULL : state->regs;
+}
+
+#define unwind_for_each_frame(state, task, regs, first_frame)	\
+	for (unwind_start(state, task, regs, first_frame);	\
+	     !unwind_done(state);				\
+	     unwind_next_frame(state))
+
+static inline void unwind_init(void) {}
+static inline void unwind_module_init(struct module *mod, void *orc_ip,
+				      size_t orc_ip_size, void *orc,
+				      size_t orc_size) {}
+
+#ifdef CONFIG_KASAN
+/*
+ * This disables KASAN checking when reading a value from another task's stack,
+ * since the other task could be running on another CPU and could have poisoned
+ * the stack in the meantime.
+ */
+#define READ_ONCE_TASK_STACK(task, x)			\
+({							\
+	unsigned long val;				\
+	if (task == current)				\
+		val = READ_ONCE(x);			\
+	else						\
+		val = READ_ONCE_NOCHECK(x);		\
+	val;						\
+})
+#else
+#define READ_ONCE_TASK_STACK(task, x) READ_ONCE(x)
+#endif
+
+#endif /* _ASM_S390_UNWIND_H */

arch/s390/kernel/Makefile

@@ -39,6 +39,7 @@ CFLAGS_smp.o		:= -Wno-nonnull
 #
 CFLAGS_stacktrace.o	+= -fno-optimize-sibling-calls
 CFLAGS_dumpstack.o	+= -fno-optimize-sibling-calls
+CFLAGS_unwind_bc.o	+= -fno-optimize-sibling-calls
 
 #
 # Pass UTS_MACHINE for user_regset definition
@@ -51,7 +52,7 @@ obj-y	+= debug.o irq.o ipl.o dis.o diag.o vdso.o early_nobss.o
 obj-y	+= sysinfo.o lgr.o os_info.o machine_kexec.o pgm_check.o
 obj-y	+= runtime_instr.o cache.o fpu.o dumpstack.o guarded_storage.o sthyi.o
 obj-y	+= entry.o reipl.o relocate_kernel.o kdebugfs.o alternative.o
-obj-y	+= nospec-branch.o ipl_vmparm.o machine_kexec_reloc.o
+obj-y	+= nospec-branch.o ipl_vmparm.o machine_kexec_reloc.o unwind_bc.o
 
 extra-y				+= head64.o vmlinux.lds
 

arch/s390/kernel/asm-offsets.c

@@ -16,6 +16,7 @@
 #include <asm/pgtable.h>
 #include <asm/gmap.h>
 #include <asm/nmi.h>
+#include <asm/stacktrace.h>
 
 int main(void)
 {