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s390/unwind: start unwinding from reliable state

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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: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
This commit is contained in:
Vasily Gorbik 2019-11-27 17:37:51 +01:00
parent de6921ccbd
commit 222ee9087a
2 changed files with 31 additions and 17 deletions
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6
arch/s390/include/asm/unwind.h
View File

@ -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)

40
arch/s390/kernel/unwind_bc.c
View File

@ -105,13 +105,11 @@ bool unwind_next_frame(struct unwind_state *state)
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);