Re: [PATCH] armv7m_nvic: set DHCSR.DEBUGEN when debugger is attached

["Alex Bennée" <alex.bennee@linaro.org>]

Valentin Ghita <valentinghita@google.com> writes:

> The DEBUGEN bit is set by the debugger when it is connected to the
> core.  Software can use this bit to check if a debug session is active.
>
> Add a function in gdbstub to check if the debugger is attached to a CPU
> and use this information when the DHCSR register is read in armv7m_nvic.
>
> Signed-off-by: Valentin Ghita <valentinghita@google.com>

Nack - use of the gdbstub should be transparent to the guest. It is not
trying to model any real JTAG/External debug hardware here.

> ---
>  gdbstub.c              | 10 ++++++++++
>  hw/intc/armv7m_nvic.c  |  4 ++++
>  include/exec/gdbstub.h |  6 ++++++
>  3 files changed, 20 insertions(+)
>
> diff --git a/gdbstub.c b/gdbstub.c
> index 3c14c6a038..d4e39db8e7 100644
> --- a/gdbstub.c
> +++ b/gdbstub.c
> @@ -3585,6 +3585,16 @@ int gdbserver_start(const char *device)
>      return 0;
>  }
>  
> +bool gdb_attached(CPUState *cpu)
> +{
> +    GDBProcess *process = gdb_get_cpu_process(cpu);
> +    if (process != NULL) {
> +        return process->attached;
> +    }
> +
> +    return false;
> +}
> +
>  static void register_types(void)
>  {
>      type_register_static(&char_gdb_type_info);
> diff --git a/hw/intc/armv7m_nvic.c b/hw/intc/armv7m_nvic.c
> index 13df002ce4..d6fff94bca 100644
> --- a/hw/intc/armv7m_nvic.c
> +++ b/hw/intc/armv7m_nvic.c
> @@ -21,6 +21,7 @@
>  #include "sysemu/runstate.h"
>  #include "target/arm/cpu.h"
>  #include "exec/exec-all.h"
> +#include "exec/gdbstub.h"
>  #include "exec/memop.h"
>  #include "qemu/log.h"
>  #include "qemu/module.h"
> @@ -1510,6 +1511,9 @@ static uint32_t nvic_readl(NVICState *s, uint32_t offset, MemTxAttrs attrs)
>          }
>          /* We provide minimal-RAS only: RFSR is RAZ/WI */
>          return 0;
> +    case 0xdf0: /* DHCSR */
> +        /* Bit 0: DEBUGEN. */
> +        return gdb_attached(CPU(cpu)) ? 1 : 0;
>      case 0xf34: /* FPCCR */
>          if (!cpu_isar_feature(aa32_vfp_simd, cpu)) {
>              return 0;
> diff --git a/include/exec/gdbstub.h b/include/exec/gdbstub.h
> index a024a0350d..383f4e5224 100644
> --- a/include/exec/gdbstub.h
> +++ b/include/exec/gdbstub.h
> @@ -177,6 +177,12 @@ static inline uint8_t * gdb_get_reg_ptr(GByteArray *buf, int len)
>   */
>  int gdbserver_start(const char *port_or_device);
>  
> +/**
> + * gdb_attached: check if GDB is attached to a given CPU.
> + * @cpu: the CPU to check if GDB is attached to.
> + */
> +bool gdb_attached(CPUState *cpu);
> +
>  /**
>   * gdb_has_xml:
>   * This is an ugly hack to cope with both new and old gdb.


-- 
Alex Bennée