Re: [Qemu-devel] [PATCH 1/2] Add GDB qAttached support

[Jan Kiszka]

On 2013-03-05 17:03, Fabien Chouteau wrote:
> With this patch GDB will issue a "detach" command at the end of a
> debugging session instead of a "kill". This behavior can be inverted
> with the new option -gdb-not-attached.
> 
> This patch implements the requirement described in Jan Kiszka's patch:
> "gdbstub: Do not kill target in system emulation mode". The patch can
> therefore be reverted.
> 
> Signed-off-by: Fabien Chouteau <address@hidden>
> ---
>  gdbstub.c              |   13 ++++++++++++-
>  include/exec/gdbstub.h |    2 ++
>  qemu-options.hx        |    7 +++++++
>  vl.c                   |    3 +++
>  4 files changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/gdbstub.c b/gdbstub.c
> index e414ad9..c0686a9 100644
> --- a/gdbstub.c
> +++ b/gdbstub.c
> @@ -32,7 +32,6 @@
>  #include "monitor/monitor.h"
>  #include "char/char.h"
>  #include "sysemu/sysemu.h"
> -#include "exec/gdbstub.h"
>  #endif
>  
>  #define MAX_PACKET_LENGTH 4096
> @@ -41,6 +40,9 @@
>  #include "qemu/sockets.h"
>  #include "sysemu/kvm.h"
>  #include "qemu/bitops.h"
> +#include "exec/gdbstub.h"
> +
> +static bool gdb_attached = true;
>  
>  #ifndef TARGET_CPU_MEMORY_RW_DEBUG
>  static inline int target_memory_rw_debug(CPUArchState *env, target_ulong 
> addr,
> @@ -2491,6 +2493,10 @@ static int gdb_handle_packet(GDBState *s, const char 
> *line_buf)
>              break;
>          }
>  #endif
> +        if (strncmp(p, "Attached", 8) == 0) {
> +            put_packet(s, gdb_attached ? "1" : "0");
> +            break;
> +        }

This works as expected for system mode, but now inverts the behaviour
for user mode - that's unexpected and not ok.

>          /* Unrecognised 'q' command.  */
>          goto unknown_command;
>  
> @@ -3055,3 +3061,8 @@ int gdbserver_start(const char *device)
>      return 0;
>  }
>  #endif
> +
> +void gdb_set_attached(bool attached)
> +{
> +    gdb_attached = attached;
> +}
> diff --git a/include/exec/gdbstub.h b/include/exec/gdbstub.h
> index ba20afa..b2d3b13 100644
> --- a/include/exec/gdbstub.h
> +++ b/include/exec/gdbstub.h
> @@ -50,4 +50,6 @@ int gdbserver_start(const char *port);
>  /* in gdbstub-xml.c, generated by scripts/feature_to_c.sh */
>  extern const char *const xml_builtin[][2];
>  
> +void gdb_set_attached(bool attached);
> +
>  #endif
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 6f9334a..026d3eb 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -2988,6 +2988,13 @@ property must be set.  These objects are placed in the
>  '/objects' path.
>  ETEXI
>  
> +DEF("gdb-not-attached", 0, QEMU_OPTION_gdb_not_attached,
> +    "-gdb-not-attached\n"
> +    "                Do not set Gdb remote server in attached mode.\n"
> +    "                When exiting debugging session, Gdb will send a 
> 'kill'\n"
> +    "                command instead of a 'detach'.\n",
> +    QEMU_ARCH_ALL)
> +

First of all, why do we need this configurable? In which use cases do
you want attached mode for user emulation or kill mode for system
emulation/virtualization?

Then, if you can convince us that such a switch is useful, a new
top-level command line option is still a no-go. We already have -gdb, so
this would have to become an option to it.

In any case, I would suggest to add static attached mode first (enabled
for system, disable for user), revert my patch and then, optionally,
propose an attached mode control.

Jan

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