On Tue, May 23, 2017 at 01:30:56PM +0900, AKASHI Takahiro wrote:
> After entering kgdb mode, 'stepi' may unexpectedly breaks the execution
> somewhere in el1_irq.
>
> This happens because a debug exception is always enabled in el1_irq
> due to the following commit merged in v3.16:
> commit 2a2830703a23 ("arm64: debug: avoid accessing mdscr_el1 on fault
> paths where possible")
> A pending interrupt can be taken after kgdb has enabled a software step,
> but before a debug exception is actually taken.
>
> This patch enforces interrupts to be masked while single stepping.
The desired behaviour here boils down to whether or not KGDB expects to step
into or over interrupts in response a stepi instruction. What do other
architectures do? What happens if the instruction being stepped faults?
Will
> Signed-off-by: AKASHI Takahiro <takahiro.aka...@linaro.org>
> Cc: Catalin Marinas <catalin.mari...@arm.com>
> Cc: Will Deacon <will.dea...@arm.com>
> Cc: Jason Wessel <jason.wes...@windriver.com>
> ---
> arch/arm64/kernel/kgdb.c | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
>
> diff --git a/arch/arm64/kernel/kgdb.c b/arch/arm64/kernel/kgdb.c
> index b9176b324e5a..fddbc6be3780 100644
> --- a/arch/arm64/kernel/kgdb.c
> +++ b/arch/arm64/kernel/kgdb.c
> @@ -28,6 +28,7 @@
>
> #include <asm/debug-monitors.h>
> #include <asm/insn.h>
> +#include <asm/ptrace.h>
> #include <asm/traps.h>
>
> struct dbg_reg_def_t dbg_reg_def[DBG_MAX_REG_NUM] = {
> @@ -111,6 +112,8 @@ struct dbg_reg_def_t dbg_reg_def[DBG_MAX_REG_NUM] = {
> { "fpcr", 4, -1 },
> };
>
> +static DEFINE_PER_CPU(unsigned int, kgdb_pstate);
> +
> char *dbg_get_reg(int regno, void *mem, struct pt_regs *regs)
> {
> if (regno >= DBG_MAX_REG_NUM || regno < 0)
> @@ -200,6 +203,10 @@ int kgdb_arch_handle_exception(int exception_vector, int
> signo,
> err = 0;
> break;
> case 's':
> + /* mask interrupts while single stepping */
> + __this_cpu_write(kgdb_pstate, linux_regs->pstate);
> + linux_regs->pstate |= PSR_I_BIT;
> +
> /*
> * Update step address value with address passed
> * with step packet.
> @@ -242,11 +249,20 @@ NOKPROBE_SYMBOL(kgdb_compiled_brk_fn);
>
> static int kgdb_step_brk_fn(struct pt_regs *regs, unsigned int esr)
> {
> + unsigned int pstate;
> +
> if (!kgdb_single_step)
> return DBG_HOOK_ERROR;
>
> kernel_disable_single_step();
>
> + /* restore interrupt mask status */
> + pstate = __this_cpu_read(kgdb_pstate);
> + if (pstate & PSR_I_BIT)
> + regs->pstate |= PSR_I_BIT;
> + else
> + regs->pstate &= ~PSR_I_BIT;
> +
> kgdb_handle_exception(1, SIGTRAP, 0, regs);
> return 0;
> }
> --
> 2.11.1
>
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