Commit 222ee908 authored by Vasily Gorbik's avatar Vasily Gorbik
Browse files

s390/unwind: start unwinding from reliable state 



A comment in arch/s390/include/asm/unwind.h says:
> 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.

With this change backchain unwinder now comply with behaviour
described. As well as matches orc unwinder implementation.  Now unwinder
starts from reliable state, i.e. __unwind_start own stack frame is
taken or stack frame generated by __switch_to (ksp) - both known to be
valid. In case of pt_regs %r15 is better match for pt_regs psw, than
sometimes random "sp" caller passed.

Reviewed-by: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: default avatarVasily Gorbik <gor@linux.ibm.com>
parent de6921cc

arch/s390/include/asm/unwind.h

+3 −3
Original line number Diff line number Diff line
@@ -58,11 +58,11 @@ static inline bool unwind_error(struct unwind_state *state) 
static inline void unwind_start(struct unwind_state *state,

				struct task_struct *task,

				struct pt_regs *regs,

				unsigned long sp)

				unsigned long first_frame)

{

	task = task ?: current;

	sp = sp ?: get_stack_pointer(task, regs);

	__unwind_start(state, task, regs, sp);

	first_frame = first_frame ?: get_stack_pointer(task, regs);

	__unwind_start(state, task, regs, first_frame);

}



static inline struct pt_regs *unwind_get_entry_regs(struct unwind_state *state)

arch/s390/kernel/unwind_bc.c

+28 −14
Original line number Diff line number Diff line
@@ -105,13 +105,11 @@ out_stop: 
EXPORT_SYMBOL_GPL(unwind_next_frame);



void __unwind_start(struct unwind_state *state, struct task_struct *task,

		    struct pt_regs *regs, unsigned long sp)

		    struct pt_regs *regs, unsigned long first_frame)

{

	struct stack_info *info = &state->stack_info;

	unsigned long *mask = &state->stack_mask;

	bool reliable;

	struct stack_frame *sf;

	unsigned long ip;

	unsigned long ip, sp;



	memset(state, 0, sizeof(*state));

	state->task = task;
@@ -123,23 +121,28 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task, 
		return;

	}



	/* Get the instruction pointer from pt_regs or the stack frame */

	if (regs) {

		ip = regs->psw.addr;

		sp = regs->gprs[15];

	} else if (task == current) {

		sp = current_frame_address();

	} else {

		sp = task->thread.ksp;

	}



	/* Get current stack pointer and initialize stack info */

	if (get_stack_info(sp, task, info, mask) != 0 ||

	    !on_stack(info, sp, sizeof(struct stack_frame))) {

	if (!update_stack_info(state, sp)) {

		/* Something is wrong with the stack pointer */

		info->type = STACK_TYPE_UNKNOWN;

		state->error = true;

		return;

	}



	/* Get the instruction pointer from pt_regs or the stack frame */

	if (regs) {

		ip = READ_ONCE_NOCHECK(regs->psw.addr);

		reliable = true;

	} else {

	if (!regs) {

		/* Stack frame is within valid stack */

		sf = (struct stack_frame *)sp;

		ip = READ_ONCE_NOCHECK(sf->gprs[8]);

		reliable = false;

	}



	ip = ftrace_graph_ret_addr(state->task, &state->graph_idx, ip, NULL);
@@ -147,6 +150,17 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task, 
	/* Update unwind state */

	state->sp = sp;

	state->ip = ip;

	state->reliable = reliable;

	state->reliable = true;



	if (!first_frame)

		return;

	/* Skip through the call chain to the specified starting frame */

	while (!unwind_done(state)) {

		if (on_stack(&state->stack_info, first_frame, sizeof(struct stack_frame))) {

			if (state->sp >= first_frame)

				break;

		}

		unwind_next_frame(state);

	}

}

EXPORT_SYMBOL_GPL(__unwind_start);

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