[PATCH] arm64: fix single step issue in kgdb

[Daniel Thompson]

On Thu, Apr 19, 2018 at 08:23:41PM +0800, Wei Li wrote:
> From: Wei Li <liwei1412 at 163.com>
> 
> In kdb, as the frontend for kgdb, cmd "ss" does not work well. It can only take effects once and the single step exception is reported as oops after a breakpoint triggered in kdb. Then the cmd "go" does not work well either due to this. Refer to the DDI0487C_a_armv8_arm.pdf (D2.12), i set the SPSR.SS=1 every time. It has been verified in qemu.
> 
> Signed-off-by: Wei Li <liwei1412 at 163.com>
> ---
>  include/asm/debug-monitors.h |    3 +++
>  kernel/debug-monitors.c      |    4 ++--
>  kernel/kgdb.c                |    3 ++-

This contains many similar changes to a patch from earlier with the same
Subject. It is a v2? If so the subject should reflect that (and a
changelog would be nice).


Daniel.


>  3 files changed, 7 insertions(+), 3 deletions(-)
>  
> diff -uprN linux-4.16.2_org/arch/arm64/include/asm/debug-monitors.h linux-4.16.2_mod/arch/arm64/include/asm/debug-monitors.h
> --- linux-4.16.2_org/arch/arm64/include/asm/debug-monitors.h    2018-04-12 18:30:01.000000000 +0800
> +++ linux-4.16.2_mod/arch/arm64/include/asm/debug-monitors.h    2018-04-19 00:19:10.134999268 +0800
> @@ -135,6 +135,9 @@ static inline int reinstall_suspended_bp
>  
>  int aarch32_break_handler(struct pt_regs *regs);
>  
> +void set_regs_spsr_ss(struct pt_regs *regs);
> +void clear_regs_spsr_ss(struct pt_regs *regs);
> +
>  #endif    /* __ASSEMBLY */
>  #endif    /* __KERNEL__ */
>  #endif    /* __ASM_DEBUG_MONITORS_H */
> diff -uprN linux-4.16.2_org/arch/arm64/kernel/debug-monitors.c linux-4.16.2_mod/arch/arm64/kernel/debug-monitors.c
> --- linux-4.16.2_org/arch/arm64/kernel/debug-monitors.c    2018-04-12 18:30:01.000000000 +0800
> +++ linux-4.16.2_mod/arch/arm64/kernel/debug-monitors.c    2018-04-19 00:19:19.435189356 +0800
> @@ -150,13 +150,13 @@ postcore_initcall(debug_monitors_init);
>  /*
>   * Single step API and exception handling.
>   */
> -static void set_regs_spsr_ss(struct pt_regs *regs)
> +void set_regs_spsr_ss(struct pt_regs *regs)
>  {
>      regs->pstate |= DBG_SPSR_SS;
>  }
>  NOKPROBE_SYMBOL(set_regs_spsr_ss);
>  
> -static void clear_regs_spsr_ss(struct pt_regs *regs)
> +void clear_regs_spsr_ss(struct pt_regs *regs)
>  {
>      regs->pstate &= ~DBG_SPSR_SS;
>  }
> diff -uprN linux-4.16.2_org/arch/arm64/kernel/kgdb.c linux-4.16.2_mod/arch/arm64/kernel/kgdb.c
> --- linux-4.16.2_org/arch/arm64/kernel/kgdb.c    2018-04-12 18:30:01.000000000 +0800
> +++ linux-4.16.2_mod/arch/arm64/kernel/kgdb.c    2018-04-19 00:19:40.892911795 +0800
> @@ -221,6 +221,7 @@ int kgdb_arch_handle_exception(int excep
>          /*
>           * Enable single step handling
>           */
> +        set_regs_spsr_ss(linux_regs);
>          if (!kernel_active_single_step())
>              kernel_enable_single_step(linux_regs);
>          err = 0;
> @@ -252,7 +253,7 @@ static int kgdb_step_brk_fn(struct pt_re
>      if (!kgdb_single_step)
>          return DBG_HOOK_ERROR;
>  
> -    kgdb_handle_exception(1, SIGTRAP, 0, regs);
> +    kgdb_handle_exception(0, SIGTRAP, 0, regs);
>      return 0;
>  }
>  NOKPROBE_SYMBOL(kgdb_step_brk_fn);
>