Re: [PATCH v5 10/10] LoongArch/ftrace: Fix unwind state when option func_stack_trace

[Qing Zhang]

On 2022/10/28 上午10:56, Huacai Chen wrote:
> Hi, Qing,
>
> Can this patch be squashed to a previous one?
ok, I'll combine this patch with the previous patch.

Thanks
- Qing

> Huacai
>
> On Mon, Sep 19, 2022 at 11:19 AM Qing Zhang <zhangqing@xxxxxxxxxxx> wrote:
> > Ftrace plays like function head exception, prologue analysis will stop soon
> > because PC is at entry.
> >
> >     90000000004c5a54 <callee>:
> >     90000000004c5a54:    03400000  andi   $zero, $zero, 0x0   ==>move  t0, ra
> >     90000000004c5a58:    03400000  andi   $zero, $zero, 0x0   ==>bl callsite
> > ==>90000000004c5a5c:    02fcc063  addi.d $sp, $sp, -208(0xf30)
> >     ...
> >
> > When encountering ftrace_call, save trace function ra at PT_ERA, save
> > parent ra at PT_R1, At this time, pc is the position after the two nops
> > of callee. There is no conventional prologue operation between this
> > position and the function entry, so we need to reset the first flag to
> > make the caller continue to unwind.
> >
> > testing method:
> >    echo path_openat > ./set_ftrace_filter
> >    echo 1 > ./options/func_stack_trace
> >    echo function > ./current_tracer
> >
> > Reported-by: Jeff Xie <xiehuan09@xxxxxxxxx>
> > Tested-by: Jinyang He <hejinyang@xxxxxxxxxxx>
> > Tested-by: Jeff Xie <xiehuan09@xxxxxxxxx>
> > Signed-off-by: Qing Zhang <zhangqing@xxxxxxxxxxx>
> > ---
> >   arch/loongarch/include/asm/unwind.h     |  2 +-
> >   arch/loongarch/kernel/unwind_prologue.c | 35 +++++++++++++++++++++----
> >   2 files changed, 31 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/loongarch/include/asm/unwind.h b/arch/loongarch/include/asm/unwind.h
> > index f66b07c3e6a1..f2b52b9ea93d 100644
> > --- a/arch/loongarch/include/asm/unwind.h
> > +++ b/arch/loongarch/include/asm/unwind.h
> > @@ -20,7 +20,7 @@ struct unwind_state {
> >          char type; /* UNWINDER_XXX */
> >          struct stack_info stack_info;
> >          struct task_struct *task;
> > -       bool first, error;
> > +       bool first, error, is_ftrace;
> >          int graph_idx;
> >          unsigned long sp, pc, ra;
> >   };
> > diff --git a/arch/loongarch/kernel/unwind_prologue.c b/arch/loongarch/kernel/unwind_prologue.c
> > index f77f3b6f3f06..4fb4923b68cc 100644
> > --- a/arch/loongarch/kernel/unwind_prologue.c
> > +++ b/arch/loongarch/kernel/unwind_prologue.c
> > @@ -14,9 +14,7 @@ unsigned long unwind_get_return_address(struct unwind_state *state)
> >
> >          if (unwind_done(state))
> >                  return 0;
> > -       else if (state->type)
> > -               return state->pc;
> > -       else if (state->first)
> > +       else if (state->type || state->first)
> >                  return state->pc;
> >
> >          return *(unsigned long *)(state->sp);
> > @@ -42,16 +40,41 @@ static bool unwind_by_guess(struct unwind_state *state)
> >          return false;
> >   }
> >
> > +static inline void unwind_state_fixup(struct unwind_state *state)
> > +{
> > +#ifdef CONFIG_FUNCTION_TRACER
> > +       static unsigned long ftrace_case = (unsigned long)ftrace_call + 4;
> > +
> > +       if (state->pc == ftrace_case)
> > +               state->is_ftrace = true;
> > +#endif
> > +}
> > +
> >   static bool unwind_by_prologue(struct unwind_state *state)
> >   {
> >          struct stack_info *info = &state->stack_info;
> >          union loongarch_instruction *ip, *ip_end;
> >          unsigned long frame_size = 0, frame_ra = -1;
> >          unsigned long size, offset, pc = state->pc;
> > +       struct pt_regs *regs;
> >
> >          if (state->sp >= info->end || state->sp < info->begin)
> >                  return false;
> >
> > +       if (state->is_ftrace) {
> > +               /*
> > +                * As we meet ftrace_regs_entry, reset first flag like first doing
> > +                * tracing, Prologue analysis will stop soon because PC is at entry.
> > +                */
> > +               regs = (struct pt_regs *)state->sp;
> > +               state->pc = regs->csr_era;
> > +               state->ra = regs->regs[1];
> > +               state->sp = regs->regs[3];
> > +               state->first = true;
> > +               state->is_ftrace = false;
> > +               return true;
> > +       }
> > +
> >          if (!kallsyms_lookup_size_offset(pc, &size, &offset))
> >                  return false;
> >
> > @@ -97,7 +120,7 @@ static bool unwind_by_prologue(struct unwind_state *state)
> >
> >          state->pc = *(unsigned long *)(state->sp + frame_ra);
> >          state->sp = state->sp + frame_size;
> > -       return !!__kernel_text_address(state->pc);
> > +       goto out;
> >
> >   first:
> >          state->first = false;
> > @@ -106,7 +129,9 @@ static bool unwind_by_prologue(struct unwind_state *state)
> >
> >          state->pc = state->ra;
> >
> > -       return !!__kernel_text_address(state->ra);
> > +out:
> > +       unwind_state_fixup(state);
> > +       return !!__kernel_text_address(state->pc);
> >   }
> >
> >   void unwind_start(struct unwind_state *state, struct task_struct *task,
> > --
> > 2.36.1