Re: [PATCH v3 5/5] LoongArch: Add generic ex-handler unwind in prologue unwinder

[Huacai Chen]

On Thu, Jan 12, 2023 at 8:41 AM Jinyang He <hejinyang@xxxxxxxxxxx> wrote:
>
> When exception is triggered, code flow go handle_\exception in some
> cases. One of stackframe in this case as follows,
>
> high -> +-------+
>         | REGS  |  <- a pt_regs
>         |       |
>         |       |  <- ex trigger
>         | REGS  |  <- ex pt_regs   <-+
>         |       |                    |
>         |       |                    |
> low  -> +-------+           ->unwind-+
>
> When unwinder unwind to handler_\exception it cannot go on prologue
> analysis. It is asynchronous code flow, we should get the next frame
> PC from regs->csr_era but not from regs->regs[1]. And we copy the
> handler codes to eentry in the early time and copy the handler codes
> to NUMA-relative memory named pcpu_handlers if NUMA is enabled. Thus,
> unwinder cannot unwind normally. Therefore, try to give some hint in
> handler_\exception and fixup it in unwind_next_frame.
>
> Reported-by: Qing Zhang <zhangqing@xxxxxxxxxxx>
> Signed-off-by: Jinyang He <hejinyang@xxxxxxxxxxx>
> ---
>  arch/loongarch/include/asm/unwind.h     |   2 +-
>  arch/loongarch/kernel/genex.S           |   3 +
>  arch/loongarch/kernel/unwind_prologue.c | 100 +++++++++++++++++++++---
>  arch/loongarch/mm/tlb.c                 |   2 +-
>  4 files changed, 92 insertions(+), 15 deletions(-)
>
> diff --git a/arch/loongarch/include/asm/unwind.h b/arch/loongarch/include/asm/unwind.h
> index cb428e1b19af..a38eb152aefb 100644
> --- a/arch/loongarch/include/asm/unwind.h
> +++ b/arch/loongarch/include/asm/unwind.h
> @@ -22,7 +22,7 @@ struct unwind_state {
>         char type; /* UNWINDER_XXX */
>         struct stack_info stack_info;
>         struct task_struct *task;
> -       bool first, error, is_ftrace;
> +       bool first, error, reset;
Hi, Qing,
Do you think is_reset is better than reset here?

>         int graph_idx;
>         unsigned long sp, pc, ra;
>  };
> diff --git a/arch/loongarch/kernel/genex.S b/arch/loongarch/kernel/genex.S
> index 75e5be807a0d..7e5c293ed89f 100644
> --- a/arch/loongarch/kernel/genex.S
> +++ b/arch/loongarch/kernel/genex.S
> @@ -67,14 +67,17 @@ SYM_FUNC_END(except_vec_cex)
>         .macro  BUILD_HANDLER exception handler prep
>         .align  5
>         SYM_FUNC_START(handle_\exception)
> +       666:
>         BACKUP_T0T1
>         SAVE_ALL
>         build_prep_\prep
>         move    a0, sp
>         la.abs  t0, do_\handler
>         jirl    ra, t0, 0
> +       668:
>         RESTORE_ALL_AND_RET
I think the 668 label should be after RESTORE_ALL_AND_RET, right?

Huacai

>         SYM_FUNC_END(handle_\exception)
> +       SYM_DATA(unwind_hint_\exception, .word 668b - 666b)
>         .endm
>
>         BUILD_HANDLER ade ade badv
> diff --git a/arch/loongarch/kernel/unwind_prologue.c b/arch/loongarch/kernel/unwind_prologue.c
> index e6c3f2ee507c..e52c18c2b604 100644
> --- a/arch/loongarch/kernel/unwind_prologue.c
> +++ b/arch/loongarch/kernel/unwind_prologue.c
> @@ -2,21 +2,100 @@
>  /*
>   * Copyright (C) 2022 Loongson Technology Corporation Limited
>   */
> +#include <linux/cpumask.h>
>  #include <linux/ftrace.h>
>  #include <linux/kallsyms.h>
>
>  #include <asm/inst.h>
> +#include <asm/loongson.h>
>  #include <asm/ptrace.h>
> +#include <asm/setup.h>
>  #include <asm/unwind.h>
>
> -static inline void unwind_state_fixup(struct unwind_state *state)
> +extern const int unwind_hint_ade;
> +extern const int unwind_hint_ale;
> +extern const int unwind_hint_bp;
> +extern const int unwind_hint_fpe;
> +extern const int unwind_hint_fpu;
> +extern const int unwind_hint_lsx;
> +extern const int unwind_hint_lasx;
> +extern const int unwind_hint_lbt;
> +extern const int unwind_hint_ri;
> +extern const int unwind_hint_watch;
> +extern unsigned long eentry;
> +#ifdef CONFIG_NUMA
> +extern unsigned long pcpu_handlers[NR_CPUS];
> +#endif
> +
> +static inline bool scan_handler(unsigned long entry_offset)
>  {
> -#ifdef CONFIG_DYNAMIC_FTRACE
> -       static unsigned long ftrace = (unsigned long)ftrace_call + 4;
> +       int idx, offset;
>
> -       if (state->pc == ftrace)
> -               state->is_ftrace = true;
> +       if (entry_offset >= EXCCODE_INT_START * VECSIZE)
> +               return false;
> +
> +       idx = entry_offset / VECSIZE;
> +       offset = entry_offset % VECSIZE;
> +       switch (idx) {
> +       case EXCCODE_ADE:
> +               return offset == unwind_hint_ade;
> +       case EXCCODE_ALE:
> +               return offset == unwind_hint_ale;
> +       case EXCCODE_BP:
> +               return offset == unwind_hint_bp;
> +       case EXCCODE_FPE:
> +               return offset == unwind_hint_fpe;
> +       case EXCCODE_FPDIS:
> +               return offset == unwind_hint_fpu;
> +       case EXCCODE_LSXDIS:
> +               return offset == unwind_hint_lsx;
> +       case EXCCODE_LASXDIS:
> +               return offset == unwind_hint_lasx;
> +       case EXCCODE_BTDIS:
> +               return offset == unwind_hint_lbt;
> +       case EXCCODE_INE:
> +               return offset == unwind_hint_ri;
> +       case EXCCODE_WATCH:
> +               return offset == unwind_hint_watch;
> +       default:
> +               return false;
> +       }
> +}
> +
> +static inline bool fix_exceptions(unsigned long pc)
> +{
> +#ifdef CONFIG_NUMA
> +       int cpu;
> +
> +       for_each_possible_cpu(cpu) {
> +               if (!pcpu_handlers[cpu])
> +                       continue;
> +               if (scan_handler(pc - pcpu_handlers[cpu]))
> +                       return true;
> +       }
>  #endif
> +       return scan_handler(pc - eentry);
> +}
> +
> +/*
> + * As we meet ftrace_regs_entry, reset first flag like first doing
> + * tracing. Prologue analysis will stop soon because PC is at entry.
> + */
> +static inline bool fix_ftrace(unsigned long pc)
> +{
> +#ifdef CONFIG_DYNAMIC_FTRACE
> +       return pc == (unsigned long)ftrace_call + LOONGARCH_INSN_SIZE;
> +#else
> +       return false;
> +#endif
> +}
> +
> +static inline bool unwind_state_fixup(struct unwind_state *state)
> +{
> +       if (!fix_exceptions(state->pc) && !fix_ftrace(state->pc))
> +               return false;
> +       state->reset = true;
> +       return true;
>  }
>
>  /*
> @@ -39,14 +118,10 @@ static bool unwind_by_prologue(struct unwind_state *state)
>         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.
> -                */
> +       if (state->reset) {
>                 regs = (struct pt_regs *)state->sp;
>                 state->first = true;
> -               state->is_ftrace = false;
> +               state->reset = false;
>                 state->pc = regs->csr_era;
>                 state->ra = regs->regs[1];
>                 state->sp = regs->regs[3];
> @@ -111,8 +186,7 @@ static bool unwind_by_prologue(struct unwind_state *state)
>
>  out:
>         state->first = false;
> -       unwind_state_fixup(state);
> -       return !!__kernel_text_address(state->pc);
> +       return unwind_state_fixup(state) || __kernel_text_address(state->pc);
>  }
>
>  static bool next_frame(struct unwind_state *state)
> diff --git a/arch/loongarch/mm/tlb.c b/arch/loongarch/mm/tlb.c
> index da3681f131c8..8bad6b0cff59 100644
> --- a/arch/loongarch/mm/tlb.c
> +++ b/arch/loongarch/mm/tlb.c
> @@ -251,7 +251,7 @@ static void output_pgtable_bits_defines(void)
>  }
>
>  #ifdef CONFIG_NUMA
> -static unsigned long pcpu_handlers[NR_CPUS];
> +unsigned long pcpu_handlers[NR_CPUS];
>  #endif
>  extern long exception_handlers[VECSIZE * 128 / sizeof(long)];
>
> --
> 2.34.3
>
>