[PATCH 1/2] Display ExceptionRecord for $_siginfo

[Simon Marchi]

On 2020-01-17 10:31 a.m., Hannes Domani via gdb-patches wrote:
> diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
> index 901e64263c..824ff4b322 100644
> --- a/gdb/windows-nat.c
> +++ b/gdb/windows-nat.c
> @@ -236,6 +236,7 @@ static DEBUG_EVENT current_event;	/* The current debug event from
>  					   WaitForDebugEvent */
>  static HANDLE current_process_handle;	/* Currently executing process */
>  static windows_thread_info *current_thread;	/* Info on currently selected thread */
> +static EXCEPTION_RECORD siginfo_er;	/* Contents of $_siginfo */

Huh... I was going to say that it shouldn't be a global variable, but a per-inferior
thing (or is it per-thread?), but pretty much all the state is already global...  so
I guess it's fine.  I gather that the windows-nat does not support debugging multiple
inferiors?  Same for win32-low in gdbserver?

>  
>  /* Counts of things.  */
>  static int exception_count = 0;
> @@ -1166,6 +1167,8 @@ handle_exception (struct target_waitstatus *ourstatus)
>    DWORD code = rec->ExceptionCode;
>    handle_exception_result result = HANDLE_EXCEPTION_HANDLED;
>  
> +  memcpy (&siginfo_er, rec, sizeof siginfo_er);
> +
>    ourstatus->kind = TARGET_WAITKIND_STOPPED;
>  
>    /* Record the context of the current thread.  */
> @@ -2862,6 +2865,7 @@ windows_nat_target::mourn_inferior ()
>        CHECK (CloseHandle (current_process_handle));
>        open_process_used = 0;
>      }
> +  siginfo_er.ExceptionCode = 0;
>    inf_child_target::mourn_inferior ();
>  }
>  
> @@ -2994,6 +2998,28 @@ windows_xfer_shared_libraries (struct target_ops *ops,
>    return len != 0 ? TARGET_XFER_OK : TARGET_XFER_EOF;
>  }
>  
> +static enum target_xfer_status
> +windows_xfer_siginfo (gdb_byte *readbuf, ULONGEST offset, ULONGEST len,
> +		      ULONGEST *xfered_len)
> +{
> +  if (!siginfo_er.ExceptionCode)

siginfo_er.ExceptionCode != 0

> +    return TARGET_XFER_E_IO;
> +
> +  if (!readbuf)

readbuf == nullptr

> +    return TARGET_XFER_E_IO;
> +
> +  if (offset > sizeof (siginfo_er))
> +    return TARGET_XFER_E_IO;
> +
> +  if (offset + len > sizeof (siginfo_er))
> +    len = sizeof (siginfo_er) - offset;
> +
> +  memcpy (readbuf, (char *) &siginfo_er + offset, len);
> +  *xfered_len = len;
> +
> +  return TARGET_XFER_OK;
> +}
> +
>  enum target_xfer_status
>  windows_nat_target::xfer_partial (enum target_object object,
>  				  const char *annex, gdb_byte *readbuf,
> @@ -3009,6 +3035,9 @@ windows_nat_target::xfer_partial (enum target_object object,
>        return windows_xfer_shared_libraries (this, object, annex, readbuf,
>  					    writebuf, offset, len, xfered_len);
>  
> +    case TARGET_OBJECT_SIGNAL_INFO:
> +      return windows_xfer_siginfo (readbuf, offset, len, xfered_len);
> +
>      default:
>        if (beneath () == NULL)
>  	{
> diff --git a/gdb/windows-tdep.c b/gdb/windows-tdep.c
> index 1fc2748581..50efa31709 100644
> --- a/gdb/windows-tdep.c
> +++ b/gdb/windows-tdep.c
> @@ -153,6 +153,26 @@ static const int FULL_TIB_SIZE = 0x1000;
>  
>  static bool maint_display_all_tib = false;
>  
> +static struct gdbarch_data *windows_gdbarch_data_handle;
> +
> +struct windows_gdbarch_data
> +  {
> +    struct type *siginfo_type;
> +  };

Unindent the curly braces and the field:

{
  struct type *siginfo_type;
}

I know there are some structures formatted this way, but the new ones we add are
aligned on column 0.

> +
> +static void *
> +init_windows_gdbarch_data (struct gdbarch *gdbarch)
> +{
> +  return GDBARCH_OBSTACK_ZALLOC (gdbarch, struct windows_gdbarch_data);
> +}
> +
> +static struct windows_gdbarch_data *
> +get_windows_gdbarch_data (struct gdbarch *gdbarch)
> +{
> +  return ((struct windows_gdbarch_data *)
> +	  gdbarch_data (gdbarch, windows_gdbarch_data_handle));
> +}
> +
>  /* Define Thread Local Base pointer type.  */
>  
>  static struct type *
> @@ -648,6 +668,43 @@ windows_gdb_signal_to_target (struct gdbarch *gdbarch, enum gdb_signal signal)
>    return -1;
>  }
>  
> +static struct type *
> +windows_get_siginfo_type (struct gdbarch *gdbarch)
> +{
> +  struct windows_gdbarch_data *windows_gdbarch_data;
> +  struct type *uint_type, *void_ptr_type;
> +  struct type *siginfo_ptr_type, *siginfo_type;
> +
> +  windows_gdbarch_data = get_windows_gdbarch_data (gdbarch);
> +  if (windows_gdbarch_data->siginfo_type != NULL)
> +    return windows_gdbarch_data->siginfo_type;
> +
> +  uint_type = arch_integer_type (gdbarch, gdbarch_int_bit (gdbarch),
> +				 1, "unsigned int");

You should be able to get this one from builtin_type (gdbarch)->builtin_unsigned_int.

> +  void_ptr_type = lookup_pointer_type (builtin_type (gdbarch)->builtin_void);
> +
> +  siginfo_type = arch_composite_type (gdbarch, "EXCEPTION_RECORD",
> +				      TYPE_CODE_STRUCT);
> +  siginfo_ptr_type = arch_pointer_type (gdbarch, gdbarch_ptr_bit (gdbarch),
> +					NULL, siginfo_type);
> +
> +  append_composite_type_field (siginfo_type, "ExceptionCode", uint_type);
> +  append_composite_type_field (siginfo_type, "ExceptionFlags", uint_type);
> +  append_composite_type_field (siginfo_type, "ExceptionRecord",
> +			       siginfo_ptr_type);
> +  append_composite_type_field (siginfo_type, "ExceptionAddress",
> +			       void_ptr_type);
> +  append_composite_type_field (siginfo_type, "NumberParameters", uint_type);
> +  append_composite_type_field_aligned (siginfo_type, "ExceptionInformation",
> +				       lookup_array_range_type (void_ptr_type,
> +								0, 14),
> +				       TYPE_LENGTH (void_ptr_type));

Shouldn't you use "DWORD" and other types named like what is found in the
real structure, instead of plain "unsigned int"?  Like what is done in
windows_get_tlb_type?

As a user, I would expect that "ptype $_siginfo" shows me "DWORD" and not
"unsigned int", don't you think?

Simon