[PATCH v2 1/2] Display ExceptionRecord for $_siginfo

[PATCH v2 1/2] Display ExceptionRecord for $_siginfo

[Hannes Domani via gdb-patches]

Uses the $_siginfo convenience variable to show the last exception.

The type looks like this:

(gdb) pt $_siginfo
type = struct EXCEPTION_RECORD {
    DWORD ExceptionCode;
    DWORD ExceptionFlags;
    struct EXCEPTION_RECORD *ExceptionRecord;
    PVOID ExceptionAddress;
    DWORD NumberParameters;
    ULONG_PTR ExceptionInformation[15];
}

EXCEPTION_RECORD is documented at [1].

Example:

Program received signal SIGSEGV, Segmentation fault.
main () at crasher.c:4
4         *(int*)0x123 = 0;
(gdb) p $_siginfo
$1 = {
  ExceptionCode = 3221225477,
  ExceptionFlags = 0,
  ExceptionRecord = 0x0,
  ExceptionAddress = 0x401632 <main+18>,
  NumberParameters = 2,
  ExceptionInformation = {1, 291, 0 <repeats 13 times>}
}
(gdb) p/x $_siginfo.ExceptionCode
$2 = 0xc0000005
(gdb) p/x $_siginfo.ExceptionInformation[1]
$3 = 0x123

And 0xc0000005 is the value of EXCEPTION_ACCESS_VIOLATION.

[1] https://docs.microsoft.com/en-us/windows/win32/api/winnt/ns-winnt-exception_record

gdb/ChangeLog:

2020-02-08  Hannes Domani  <ssbssa@yahoo.de>

	* windows-nat.c (handle_exception): Set siginfo_er.
	(windows_nat_target::mourn_inferior): Reset siginfo_er.
	(windows_xfer_siginfo): New function.
	(windows_nat_target::xfer_partial): Call windows_xfer_siginfo.
	* windows-tdep.c (struct windows_gdbarch_data): New struct.
	(init_windows_gdbarch_data): New function.
	(get_windows_gdbarch_data): New function.
	(windows_get_siginfo_type): New function.
	(windows_init_abi): Register windows_get_siginfo_type.
	(_initialize_windows_tdep): Register init_windows_gdbarch_data.

gdbserver/ChangeLog:

2020-02-08  Hannes Domani  <ssbssa@yahoo.de>

	* win32-low.c (win32_clear_inferiors): Reset siginfo_er.
	(handle_exception): Set siginfo_er.
	(win32_xfer_siginfo): New function.
---
v2:
- coding style fixes
- more comments
- use documented field type names in EXCEPTION_RECORD
---
 gdb/windows-nat.c     | 31 +++++++++++++++++++
 gdb/windows-tdep.c    | 72 +++++++++++++++++++++++++++++++++++++++++++
 gdbserver/win32-low.c | 30 +++++++++++++++++-
 3 files changed, 132 insertions(+), 1 deletion(-)

diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index 366c98fbf3..76fcdd6bd4 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 */
 
 /* Counts of things.  */
 static int exception_count = 0;
@@ -1167,6 +1168,8 @@ 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.  */
@@ -2863,6 +2866,7 @@ windows_nat_target::mourn_inferior ()
       CHECK (CloseHandle (current_process_handle));
       open_process_used = 0;
     }
+  siginfo_er.ExceptionCode = 0;
   inf_child_target::mourn_inferior ();
 }
 
@@ -2996,6 +3000,30 @@ windows_xfer_shared_libraries (struct target_ops *ops,
   return len != 0 ? TARGET_XFER_OK : TARGET_XFER_EOF;
 }
 
+/* Helper for windows_nat_target::xfer_partial that handles signal info.  */
+
+static enum target_xfer_status
+windows_xfer_siginfo (gdb_byte *readbuf, ULONGEST offset, ULONGEST len,
+		      ULONGEST *xfered_len)
+{
+  if (siginfo_er.ExceptionCode == 0)
+    return TARGET_XFER_E_IO;
+
+  if (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,
@@ -3011,6 +3039,9 @@ 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 6c9632d035..ad65b1b403 100644
--- a/gdb/windows-tdep.c
+++ b/gdb/windows-tdep.c
@@ -153,6 +153,30 @@ 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;
+};
+
+/* Allocate windows_gdbarch_data for an arch.  */
+
+static void *
+init_windows_gdbarch_data (struct gdbarch *gdbarch)
+{
+  return GDBARCH_OBSTACK_ZALLOC (gdbarch, struct windows_gdbarch_data);
+}
+
+/* Get windows_gdbarch_data of an arch.  */
+
+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 *
@@ -656,6 +680,49 @@ windows_gdb_signal_to_target (struct gdbarch *gdbarch, enum gdb_signal signal)
   return -1;
 }
 
+/* Implement the "get_siginfo_type" gdbarch method.  */
+
+static struct type *
+windows_get_siginfo_type (struct gdbarch *gdbarch)
+{
+  struct windows_gdbarch_data *windows_gdbarch_data;
+  struct type *dword_type, *pvoid_type, *ulongptr_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;
+
+  dword_type = arch_integer_type (gdbarch, gdbarch_int_bit (gdbarch),
+				  1, "DWORD");
+  pvoid_type = arch_pointer_type (gdbarch, gdbarch_ptr_bit (gdbarch), "PVOID",
+				  builtin_type (gdbarch)->builtin_void);
+  ulongptr_type = arch_integer_type (gdbarch, gdbarch_ptr_bit (gdbarch),
+				     1, "ULONG_PTR");
+
+  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", dword_type);
+  append_composite_type_field (siginfo_type, "ExceptionFlags", dword_type);
+  append_composite_type_field (siginfo_type, "ExceptionRecord",
+			       siginfo_ptr_type);
+  append_composite_type_field (siginfo_type, "ExceptionAddress",
+			       pvoid_type);
+  append_composite_type_field (siginfo_type, "NumberParameters", dword_type);
+  /* The 64-bit variant needs some padding.  */
+  append_composite_type_field_aligned (siginfo_type, "ExceptionInformation",
+				       lookup_array_range_type (ulongptr_type,
+								0, 14),
+				       TYPE_LENGTH (ulongptr_type));
+
+  windows_gdbarch_data->siginfo_type = siginfo_type;
+
+  return siginfo_type;
+}
+
 /* To be called from the various GDB_OSABI_CYGWIN handlers for the
    various Windows architectures and machine types.  */
 
@@ -675,6 +742,8 @@ windows_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
   set_gdbarch_gdb_signal_to_target (gdbarch, windows_gdb_signal_to_target);
 
   set_solib_ops (gdbarch, &solib_target_so_ops);
+
+  set_gdbarch_get_siginfo_type (gdbarch, windows_get_siginfo_type);
 }
 
 /* Implementation of `tlb' variable.  */
@@ -690,6 +759,9 @@ void _initialize_windows_tdep ();
 void
 _initialize_windows_tdep ()
 {
+  windows_gdbarch_data_handle
+    = gdbarch_data_register_post_init (init_windows_gdbarch_data);
+
   init_w32_command_list ();
   add_cmd ("thread-information-block", class_info, display_tib,
 	   _("Display thread information block."),
diff --git a/gdbserver/win32-low.c b/gdbserver/win32-low.c
index 2c4a9b1074..9d0343788f 100644
--- a/gdbserver/win32-low.c
+++ b/gdbserver/win32-low.c
@@ -75,6 +75,7 @@ static int attaching = 0;
 static HANDLE current_process_handle = NULL;
 static DWORD current_process_id = 0;
 static DWORD main_thread_id = 0;
+static EXCEPTION_RECORD siginfo_er;	/* Contents of $_siginfo */
 static enum gdb_signal last_sig = GDB_SIGNAL_0;
 
 /* The current debug event from WaitForDebugEvent.  */
@@ -801,6 +802,7 @@ win32_clear_inferiors (void)
     CloseHandle (current_process_handle);
 
   for_each_thread (delete_thread_info);
+  siginfo_er.ExceptionCode = 0;
   clear_inferiors ();
 }
 
@@ -1230,6 +1232,9 @@ handle_exception (struct target_waitstatus *ourstatus)
 {
   DWORD code = current_event.u.Exception.ExceptionRecord.ExceptionCode;
 
+  memcpy (&siginfo_er, &current_event.u.Exception.ExceptionRecord,
+	  sizeof siginfo_er);
+
   ourstatus->kind = TARGET_WAITKIND_STOPPED;
 
   switch (code)
@@ -1772,6 +1777,29 @@ wince_hostio_last_error (char *buf)
 }
 #endif
 
+/* Write Windows signal info.  */
+
+static int
+win32_xfer_siginfo (const char *annex, unsigned char *readbuf,
+		    unsigned const char *writebuf, CORE_ADDR offset, int len)
+{
+  if (siginfo_er.ExceptionCode == 0)
+    return -1;
+
+  if (readbuf == nullptr)
+    return -1;
+
+  if (offset > sizeof (siginfo_er))
+    return -1;
+
+  if (offset + len > sizeof (siginfo_er))
+    len = sizeof (siginfo_er) - offset;
+
+  memcpy (readbuf, (char *) &siginfo_er + offset, len);
+
+  return len;
+}
+
 /* Write Windows OS Thread Information Block address.  */
 
 static int
@@ -1833,7 +1861,7 @@ static process_stratum_target win32_target_ops = {
   hostio_last_error_from_errno,
 #endif
   NULL, /* qxfer_osdata */
-  NULL, /* qxfer_siginfo */
+  win32_xfer_siginfo,
   NULL, /* supports_non_stop */
   NULL, /* async */
   NULL, /* start_non_stop */
-- 
2.25.0

[PATCH v2 2/2] Use enums for human-readable exception information.

[Hannes Domani via gdb-patches]

Changes to $_siginfo type to this:

(gdb) pt $_siginfo
type = struct EXCEPTION_RECORD {
    enum ExceptionCode ExceptionCode;
    DWORD ExceptionFlags;
    struct EXCEPTION_RECORD *ExceptionRecord;
    PVOID ExceptionAddress;
    DWORD NumberParameters;
    union {
        ULONG_PTR ExceptionInformation[15];
        struct {...} AccessViolationInformation;
    };
}
(gdb) pt $_siginfo.ExceptionCode
type = enum ExceptionCode {FATAL_APP_EXIT = 1073741845,
    DBG_CONTROL_C = 1073807365, DBG_CONTROL_BREAK = 1073807368,
    DATATYPE_MISALIGNMENT = 2147483650, BREAKPOINT, SINGLE_STEP,
    ACCESS_VIOLATION = 3221225477, IN_PAGE_ERROR,
    ILLEGAL_INSTRUCTION = 3221225501, NONCONTINUABLE_EXCEPTION = 3221225509,
    INVALID_DISPOSITION, ARRAY_BOUNDS_EXCEEDED = 3221225612,
    FLOAT_DENORMAL_OPERAND, FLOAT_DIVIDE_BY_ZERO, FLOAT_INEXACT_RESULT,
    FLOAT_INVALID_OPERATION, FLOAT_OVERFLOW, FLOAT_STACK_CHECK,
    FLOAT_UNDERFLOW, INTEGER_DIVIDE_BY_ZERO, INTEGER_OVERFLOW,
    PRIV_INSTRUCTION, STACK_OVERFLOW = 3221225725, FAST_FAIL = 3221226505}
(gdb) pt $_siginfo.AccessViolationInformation
type = struct {
    enum ViolationType Type;
    PVOID Address;
}
(gdb) pt $_siginfo.AccessViolationInformation.Type
type = enum ViolationType {READ_ACCESS_VIOLATION, WRITE_ACCESS_VIOLATION,
    DATA_EXECUTION_PREVENTION_VIOLATION = 8}

Which makes it easier to understand the reason of the exception:

(gdb) p $_siginfo
$1 = {
  ExceptionCode = ACCESS_VIOLATION,
  ExceptionFlags = 0,
  ExceptionRecord = 0x0,
  ExceptionAddress = 0x401632 <main+18>,
  NumberParameters = 2,
  {
    ExceptionInformation = {1, 291, 0 <repeats 13 times>},
    AccessViolationInformation = {
      Type = WRITE_ACCESS_VIOLATION,
      Address = 0x123
    }
  }
}

gdb/ChangeLog:

2020-02-08  Hannes Domani  <ssbssa@yahoo.de>

	* windows-tdep.c (struct enum_value_name): New struct.
	(create_enum): New function.
	(windows_get_siginfo_type): Create and use enum types.
---
v2:
- more comments
---
 gdb/windows-tdep.c | 102 ++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 96 insertions(+), 6 deletions(-)

diff --git a/gdb/windows-tdep.c b/gdb/windows-tdep.c
index ad65b1b403..e9787887a4 100644
--- a/gdb/windows-tdep.c
+++ b/gdb/windows-tdep.c
@@ -680,6 +680,71 @@ windows_gdb_signal_to_target (struct gdbarch *gdbarch, enum gdb_signal signal)
   return -1;
 }
 
+struct enum_value_name
+{
+  uint32_t value;
+  const char *name;
+};
+
+/* Allocate a TYPE_CODE_ENUM type structure with its named values.  */
+
+static struct type *
+create_enum (struct gdbarch *gdbarch, int bit, const char *name,
+	     const struct enum_value_name *values, int count)
+{
+  struct type *type;
+  int i;
+
+  type = arch_type (gdbarch, TYPE_CODE_ENUM, bit, name);
+  TYPE_NFIELDS (type) = count;
+  TYPE_FIELDS (type) = (struct field *)
+    TYPE_ZALLOC (type, sizeof (struct field) * count);
+  TYPE_UNSIGNED (type) = 1;
+
+  for (i = 0; i < count; i++)
+  {
+    TYPE_FIELD_NAME (type, i) = values[i].name;
+    SET_FIELD_ENUMVAL (TYPE_FIELD (type, i), values[i].value);
+  }
+
+  return type;
+}
+
+static const struct enum_value_name exception_values[] =
+{
+  { 0x40000015, "FATAL_APP_EXIT" },
+  { 0x40010005, "DBG_CONTROL_C" },
+  { 0x40010008, "DBG_CONTROL_BREAK" },
+  { 0x80000002, "DATATYPE_MISALIGNMENT" },
+  { 0x80000003, "BREAKPOINT" },
+  { 0x80000004, "SINGLE_STEP" },
+  { 0xC0000005, "ACCESS_VIOLATION" },
+  { 0xC0000006, "IN_PAGE_ERROR" },
+  { 0xC000001D, "ILLEGAL_INSTRUCTION" },
+  { 0xC0000025, "NONCONTINUABLE_EXCEPTION" },
+  { 0xC0000026, "INVALID_DISPOSITION" },
+  { 0xC000008C, "ARRAY_BOUNDS_EXCEEDED" },
+  { 0xC000008D, "FLOAT_DENORMAL_OPERAND" },
+  { 0xC000008E, "FLOAT_DIVIDE_BY_ZERO" },
+  { 0xC000008F, "FLOAT_INEXACT_RESULT" },
+  { 0xC0000090, "FLOAT_INVALID_OPERATION" },
+  { 0xC0000091, "FLOAT_OVERFLOW" },
+  { 0xC0000092, "FLOAT_STACK_CHECK" },
+  { 0xC0000093, "FLOAT_UNDERFLOW" },
+  { 0xC0000094, "INTEGER_DIVIDE_BY_ZERO" },
+  { 0xC0000095, "INTEGER_OVERFLOW" },
+  { 0xC0000096, "PRIV_INSTRUCTION" },
+  { 0xC00000FD, "STACK_OVERFLOW" },
+  { 0xC0000409, "FAST_FAIL" },
+};
+
+static const struct enum_value_name violation_values[] =
+{
+  { 0, "READ_ACCESS_VIOLATION" },
+  { 1, "WRITE_ACCESS_VIOLATION" },
+  { 8, "DATA_EXECUTION_PREVENTION_VIOLATION" },
+};
+
 /* Implement the "get_siginfo_type" gdbarch method.  */
 
 static struct type *
@@ -687,7 +752,8 @@ windows_get_siginfo_type (struct gdbarch *gdbarch)
 {
   struct windows_gdbarch_data *windows_gdbarch_data;
   struct type *dword_type, *pvoid_type, *ulongptr_type;
-  struct type *siginfo_ptr_type, *siginfo_type;
+  struct type *code_enum, *violation_enum;
+  struct type *violation_type, *para_type, *siginfo_ptr_type, *siginfo_type;
 
   windows_gdbarch_data = get_windows_gdbarch_data (gdbarch);
   if (windows_gdbarch_data->siginfo_type != NULL)
@@ -700,12 +766,38 @@ windows_get_siginfo_type (struct gdbarch *gdbarch)
   ulongptr_type = arch_integer_type (gdbarch, gdbarch_ptr_bit (gdbarch),
 				     1, "ULONG_PTR");
 
+  /* ExceptionCode value names */
+  code_enum = create_enum (gdbarch, gdbarch_int_bit (gdbarch),
+			   "ExceptionCode", exception_values,
+			   ARRAY_SIZE (exception_values));
+
+  /* ACCESS_VIOLATION type names */
+  violation_enum = create_enum (gdbarch, gdbarch_ptr_bit (gdbarch),
+				"ViolationType", violation_values,
+				ARRAY_SIZE (violation_values));
+
+  /* ACCESS_VIOLATION information */
+  violation_type = arch_composite_type (gdbarch, NULL, TYPE_CODE_STRUCT);
+  append_composite_type_field (violation_type, "Type", violation_enum);
+  append_composite_type_field (violation_type, "Address", pvoid_type);
+
+  /* Unnamed union of the documented field ExceptionInformation,
+     and the alternative AccessViolationInformation (which displays
+     human-readable values for ExceptionCode ACCESS_VIOLATION).  */
+  para_type = arch_composite_type (gdbarch, NULL, TYPE_CODE_UNION);
+  append_composite_type_field (para_type, "ExceptionInformation",
+			       lookup_array_range_type (ulongptr_type, 0, 14));
+  append_composite_type_field (para_type, "AccessViolationInformation",
+			       violation_type);
+
   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", dword_type);
+  /* ExceptionCode is documented as type DWORD, but here a helper
+     enum type is used instead to display a human-readable value.  */
+  append_composite_type_field (siginfo_type, "ExceptionCode", code_enum);
   append_composite_type_field (siginfo_type, "ExceptionFlags", dword_type);
   append_composite_type_field (siginfo_type, "ExceptionRecord",
 			       siginfo_ptr_type);
@@ -713,10 +805,8 @@ windows_get_siginfo_type (struct gdbarch *gdbarch)
 			       pvoid_type);
   append_composite_type_field (siginfo_type, "NumberParameters", dword_type);
   /* The 64-bit variant needs some padding.  */
-  append_composite_type_field_aligned (siginfo_type, "ExceptionInformation",
-				       lookup_array_range_type (ulongptr_type,
-								0, 14),
-				       TYPE_LENGTH (ulongptr_type));
+  append_composite_type_field_aligned (siginfo_type, "",
+				       para_type, TYPE_LENGTH (ulongptr_type));
 
   windows_gdbarch_data->siginfo_type = siginfo_type;
 
-- 
2.25.0

Re: [PATCH v2 2/2] Use enums for human-readable exception information.

[Simon Marchi]

On 2020-02-08 11:26 a.m., Hannes Domani via gdb-patches wrote:
> Changes to $_siginfo type to this:
> 
> (gdb) pt $_siginfo
> type = struct EXCEPTION_RECORD {
>     enum ExceptionCode ExceptionCode;
>     DWORD ExceptionFlags;
>     struct EXCEPTION_RECORD *ExceptionRecord;
>     PVOID ExceptionAddress;
>     DWORD NumberParameters;
>     union {
>         ULONG_PTR ExceptionInformation[15];
>         struct {...} AccessViolationInformation;
>     };
> }
> (gdb) pt $_siginfo.ExceptionCode
> type = enum ExceptionCode {FATAL_APP_EXIT = 1073741845,
>     DBG_CONTROL_C = 1073807365, DBG_CONTROL_BREAK = 1073807368,
>     DATATYPE_MISALIGNMENT = 2147483650, BREAKPOINT, SINGLE_STEP,
>     ACCESS_VIOLATION = 3221225477, IN_PAGE_ERROR,
>     ILLEGAL_INSTRUCTION = 3221225501, NONCONTINUABLE_EXCEPTION = 3221225509,
>     INVALID_DISPOSITION, ARRAY_BOUNDS_EXCEEDED = 3221225612,
>     FLOAT_DENORMAL_OPERAND, FLOAT_DIVIDE_BY_ZERO, FLOAT_INEXACT_RESULT,
>     FLOAT_INVALID_OPERATION, FLOAT_OVERFLOW, FLOAT_STACK_CHECK,
>     FLOAT_UNDERFLOW, INTEGER_DIVIDE_BY_ZERO, INTEGER_OVERFLOW,
>     PRIV_INSTRUCTION, STACK_OVERFLOW = 3221225725, FAST_FAIL = 3221226505}
> (gdb) pt $_siginfo.AccessViolationInformation
> type = struct {
>     enum ViolationType Type;
>     PVOID Address;
> }
> (gdb) pt $_siginfo.AccessViolationInformation.Type
> type = enum ViolationType {READ_ACCESS_VIOLATION, WRITE_ACCESS_VIOLATION,
>     DATA_EXECUTION_PREVENTION_VIOLATION = 8}
> 
> Which makes it easier to understand the reason of the exception:
> 
> (gdb) p $_siginfo
> $1 = {
>   ExceptionCode = ACCESS_VIOLATION,
>   ExceptionFlags = 0,
>   ExceptionRecord = 0x0,
>   ExceptionAddress = 0x401632 <main+18>,
>   NumberParameters = 2,
>   {
>     ExceptionInformation = {1, 291, 0 <repeats 13 times>},
>     AccessViolationInformation = {
>       Type = WRITE_ACCESS_VIOLATION,
>       Address = 0x123
>     }
>   }
> }
> 
> gdb/ChangeLog:
> 
> 2020-02-08  Hannes Domani  <ssbssa@yahoo.de>
> 
> 	* windows-tdep.c (struct enum_value_name): New struct.
> 	(create_enum): New function.
> 	(windows_get_siginfo_type): Create and use enum types.
> ---
> v2:
> - more comments
> ---
>  gdb/windows-tdep.c | 102 ++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 96 insertions(+), 6 deletions(-)
> 
> diff --git a/gdb/windows-tdep.c b/gdb/windows-tdep.c
> index ad65b1b403..e9787887a4 100644
> --- a/gdb/windows-tdep.c
> +++ b/gdb/windows-tdep.c
> @@ -680,6 +680,71 @@ windows_gdb_signal_to_target (struct gdbarch *gdbarch, enum gdb_signal signal)
>    return -1;
>  }
>  
> +struct enum_value_name
> +{
> +  uint32_t value;
> +  const char *name;
> +};
> +
> +/* Allocate a TYPE_CODE_ENUM type structure with its named values.  */
> +
> +static struct type *
> +create_enum (struct gdbarch *gdbarch, int bit, const char *name,
> +	     const struct enum_value_name *values, int count)
> +{
> +  struct type *type;
> +  int i;
> +
> +  type = arch_type (gdbarch, TYPE_CODE_ENUM, bit, name);
> +  TYPE_NFIELDS (type) = count;
> +  TYPE_FIELDS (type) = (struct field *)
> +    TYPE_ZALLOC (type, sizeof (struct field) * count);
> +  TYPE_UNSIGNED (type) = 1;
> +
> +  for (i = 0; i < count; i++)
> +  {
> +    TYPE_FIELD_NAME (type, i) = values[i].name;
> +    SET_FIELD_ENUMVAL (TYPE_FIELD (type, i), values[i].value);
> +  }
> +
> +  return type;
> +}
> +
> +static const struct enum_value_name exception_values[] =
> +{
> +  { 0x40000015, "FATAL_APP_EXIT" },
> +  { 0x40010005, "DBG_CONTROL_C" },
> +  { 0x40010008, "DBG_CONTROL_BREAK" },
> +  { 0x80000002, "DATATYPE_MISALIGNMENT" },
> +  { 0x80000003, "BREAKPOINT" },
> +  { 0x80000004, "SINGLE_STEP" },
> +  { 0xC0000005, "ACCESS_VIOLATION" },
> +  { 0xC0000006, "IN_PAGE_ERROR" },
> +  { 0xC000001D, "ILLEGAL_INSTRUCTION" },
> +  { 0xC0000025, "NONCONTINUABLE_EXCEPTION" },
> +  { 0xC0000026, "INVALID_DISPOSITION" },
> +  { 0xC000008C, "ARRAY_BOUNDS_EXCEEDED" },
> +  { 0xC000008D, "FLOAT_DENORMAL_OPERAND" },
> +  { 0xC000008E, "FLOAT_DIVIDE_BY_ZERO" },
> +  { 0xC000008F, "FLOAT_INEXACT_RESULT" },
> +  { 0xC0000090, "FLOAT_INVALID_OPERATION" },
> +  { 0xC0000091, "FLOAT_OVERFLOW" },
> +  { 0xC0000092, "FLOAT_STACK_CHECK" },
> +  { 0xC0000093, "FLOAT_UNDERFLOW" },
> +  { 0xC0000094, "INTEGER_DIVIDE_BY_ZERO" },
> +  { 0xC0000095, "INTEGER_OVERFLOW" },
> +  { 0xC0000096, "PRIV_INSTRUCTION" },
> +  { 0xC00000FD, "STACK_OVERFLOW" },
> +  { 0xC0000409, "FAST_FAIL" },
> +};
> +
> +static const struct enum_value_name violation_values[] =
> +{
> +  { 0, "READ_ACCESS_VIOLATION" },
> +  { 1, "WRITE_ACCESS_VIOLATION" },
> +  { 8, "DATA_EXECUTION_PREVENTION_VIOLATION" },
> +};
> +
>  /* Implement the "get_siginfo_type" gdbarch method.  */
>  
>  static struct type *
> @@ -687,7 +752,8 @@ windows_get_siginfo_type (struct gdbarch *gdbarch)
>  {
>    struct windows_gdbarch_data *windows_gdbarch_data;
>    struct type *dword_type, *pvoid_type, *ulongptr_type;
> -  struct type *siginfo_ptr_type, *siginfo_type;
> +  struct type *code_enum, *violation_enum;
> +  struct type *violation_type, *para_type, *siginfo_ptr_type, *siginfo_type;
>  
>    windows_gdbarch_data = get_windows_gdbarch_data (gdbarch);
>    if (windows_gdbarch_data->siginfo_type != NULL)
> @@ -700,12 +766,38 @@ windows_get_siginfo_type (struct gdbarch *gdbarch)
>    ulongptr_type = arch_integer_type (gdbarch, gdbarch_ptr_bit (gdbarch),
>  				     1, "ULONG_PTR");
>  
> +  /* ExceptionCode value names */
> +  code_enum = create_enum (gdbarch, gdbarch_int_bit (gdbarch),
> +			   "ExceptionCode", exception_values,
> +			   ARRAY_SIZE (exception_values));
> +
> +  /* ACCESS_VIOLATION type names */
> +  violation_enum = create_enum (gdbarch, gdbarch_ptr_bit (gdbarch),
> +				"ViolationType", violation_values,
> +				ARRAY_SIZE (violation_values));
> +
> +  /* ACCESS_VIOLATION information */
> +  violation_type = arch_composite_type (gdbarch, NULL, TYPE_CODE_STRUCT);
> +  append_composite_type_field (violation_type, "Type", violation_enum);
> +  append_composite_type_field (violation_type, "Address", pvoid_type);
> +
> +  /* Unnamed union of the documented field ExceptionInformation,
> +     and the alternative AccessViolationInformation (which displays
> +     human-readable values for ExceptionCode ACCESS_VIOLATION).  */
> +  para_type = arch_composite_type (gdbarch, NULL, TYPE_CODE_UNION);
> +  append_composite_type_field (para_type, "ExceptionInformation",
> +			       lookup_array_range_type (ulongptr_type, 0, 14));
> +  append_composite_type_field (para_type, "AccessViolationInformation",
> +			       violation_type);
> +
>    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", dword_type);
> +  /* ExceptionCode is documented as type DWORD, but here a helper
> +     enum type is used instead to display a human-readable value.  */
> +  append_composite_type_field (siginfo_type, "ExceptionCode", code_enum);
>    append_composite_type_field (siginfo_type, "ExceptionFlags", dword_type);
>    append_composite_type_field (siginfo_type, "ExceptionRecord",
>  			       siginfo_ptr_type);
> @@ -713,10 +805,8 @@ windows_get_siginfo_type (struct gdbarch *gdbarch)
>  			       pvoid_type);
>    append_composite_type_field (siginfo_type, "NumberParameters", dword_type);
>    /* The 64-bit variant needs some padding.  */
> -  append_composite_type_field_aligned (siginfo_type, "ExceptionInformation",
> -				       lookup_array_range_type (ulongptr_type,
> -								0, 14),
> -				       TYPE_LENGTH (ulongptr_type));
> +  append_composite_type_field_aligned (siginfo_type, "",
> +				       para_type, TYPE_LENGTH (ulongptr_type));
>  
>    windows_gdbarch_data->siginfo_type = siginfo_type;
>  
> -- 
> 2.25.0
> 

Eli, same question here.  This makes GDB's EXCEPTION_RECORD type deviate from
the official one, but just to improve readability when you print it.   I think
it's a good idea, but I'd like to hear what you think.

And again, should we document this behavior in the manual, or is it obvious and
discoverable enough by itself (when the user prints $_siginfo, it should be
self-explanatory, if they already know about the real EXCEPTION_RECORD type).

Simon

Re: [PATCH v2 2/2] Use enums for human-readable exception information.

[Eli Zaretskii]

> From: Simon Marchi <simark@simark.ca>
> Date: Sat, 8 Feb 2020 15:04:23 -0500
> 
> Eli, same question here.  This makes GDB's EXCEPTION_RECORD type deviate from
> the official one, but just to improve readability when you print it.   I think
> it's a good idea, but I'd like to hear what you think.

This LGTM.

> And again, should we document this behavior in the manual, or is it obvious and
> discoverable enough by itself (when the user prints $_siginfo, it should be
> self-explanatory, if they already know about the real EXCEPTION_RECORD type).

Only in NEWS, I think.

Thanks.

Re: [PATCH v2 1/2] Display ExceptionRecord for $_siginfo

[Simon Marchi]

On 2020-02-08 11:26 a.m., Hannes Domani via gdb-patches wrote:
> Uses the $_siginfo convenience variable to show the last exception.
> 
> The type looks like this:
> 
> (gdb) pt $_siginfo
> type = struct EXCEPTION_RECORD {
>     DWORD ExceptionCode;
>     DWORD ExceptionFlags;
>     struct EXCEPTION_RECORD *ExceptionRecord;
>     PVOID ExceptionAddress;
>     DWORD NumberParameters;
>     ULONG_PTR ExceptionInformation[15];
> }
> 
> EXCEPTION_RECORD is documented at [1].
> 
> Example:
> 
> Program received signal SIGSEGV, Segmentation fault.
> main () at crasher.c:4
> 4         *(int*)0x123 = 0;
> (gdb) p $_siginfo
> $1 = {
>   ExceptionCode = 3221225477,
>   ExceptionFlags = 0,
>   ExceptionRecord = 0x0,
>   ExceptionAddress = 0x401632 <main+18>,
>   NumberParameters = 2,
>   ExceptionInformation = {1, 291, 0 <repeats 13 times>}
> }
> (gdb) p/x $_siginfo.ExceptionCode
> $2 = 0xc0000005
> (gdb) p/x $_siginfo.ExceptionInformation[1]
> $3 = 0x123
> 
> And 0xc0000005 is the value of EXCEPTION_ACCESS_VIOLATION.
> 
> [1] https://docs.microsoft.com/en-us/windows/win32/api/winnt/ns-winnt-exception_record

Eli, could you please comment on this from a Windows user point of view, if this looks
correct to you?  Also, does this need a manual/NEWS update?

The patch otherwise looks ok to me.

Simon

Re: [PATCH v2 1/2] Display ExceptionRecord for $_siginfo

[Eli Zaretskii]

> From: Simon Marchi <simark@simark.ca>
> Date: Sat, 8 Feb 2020 15:00:10 -0500
> 
> > Program received signal SIGSEGV, Segmentation fault.
> > main () at crasher.c:4
> > 4         *(int*)0x123 = 0;
> > (gdb) p $_siginfo
> > $1 = {
> >   ExceptionCode = 3221225477,
> >   ExceptionFlags = 0,
> >   ExceptionRecord = 0x0,
> >   ExceptionAddress = 0x401632 <main+18>,
> >   NumberParameters = 2,
> >   ExceptionInformation = {1, 291, 0 <repeats 13 times>}
> > }
> > (gdb) p/x $_siginfo.ExceptionCode
> > $2 = 0xc0000005
> > (gdb) p/x $_siginfo.ExceptionInformation[1]
> > $3 = 0x123
> > 
> > And 0xc0000005 is the value of EXCEPTION_ACCESS_VIOLATION.
> > 
> > [1] https://docs.microsoft.com/en-us/windows/win32/api/winnt/ns-winnt-exception_record
> 
> Eli, could you please comment on this from a Windows user point of view, if this looks
> correct to you?

LGTM, although I'd prefer to have ExceptionCode be printed in hex by
default.  But I guess that could be tricky, and the next patch makes
then print as symbolic names anyway.

> Also, does this need a manual/NEWS update?

I think only NEWS, because the manual already says "on some targets",
and gives an example from GNU/Linux only.

Thanks.

Re: [PATCH v2 1/2] Display ExceptionRecord for $_siginfo

[Hannes Domani via gdb-patches]

 Am Samstag, 8. Februar 2020, 21:13:54 MEZ hat Eli Zaretskii <eliz@gnu.org> Folgendes geschrieben:

> > From: Simon Marchi <simark@simark.ca>
> > Date: Sat, 8 Feb 2020 15:00:10 -0500
> >
> > > Program received signal SIGSEGV, Segmentation fault.
> > > main () at crasher.c:4
> > > 4        *(int*)0x123 = 0;
> > > (gdb) p $_siginfo
> > > $1 = {
> > >  ExceptionCode = 3221225477,
> > >  ExceptionFlags = 0,
> > >  ExceptionRecord = 0x0,
> > >  ExceptionAddress = 0x401632 <main+18>,
> > >  NumberParameters = 2,
> > >  ExceptionInformation = {1, 291, 0 <repeats 13 times>}
> > > }
> > > (gdb) p/x $_siginfo.ExceptionCode
> > > $2 = 0xc0000005
> > > (gdb) p/x $_siginfo.ExceptionInformation[1]
> > > $3 = 0x123
> > >
> > > And 0xc0000005 is the value of EXCEPTION_ACCESS_VIOLATION.
> > >
> > > [1] https://docs.microsoft.com/en-us/windows/win32/api/winnt/ns-winnt-exception_record
> >
> > Eli, could you please comment on this from a Windows user point of view, if this looks
> > correct to you?
>
> LGTM, although I'd prefer to have ExceptionCode be printed in hex by
> default.  But I guess that could be tricky, and the next patch makes
> then print as symbolic names anyway.

These were basically the same thoughts I had when I made this.


> > Also, does this need a manual/NEWS update?
>
>
> I think only NEWS, because the manual already says "on some targets",
> and gives an example from GNU/Linux only.

Is it fine if I add the following to this patch?:

    * NEWS: Mention $_siginfo support for Windows.
---
diff --git a/gdb/NEWS b/gdb/NEWS
index d4e2e70f38..c202fe06de 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -10,6 +10,9 @@
   that support it (see entry for GDB 9, below), providing faster
   performance for programs with many symbols.

+* The $_siginfo convenience variable now also works on Windows targets,
+  and will display the EXCEPTION_RECORD of the last handled exception.
+
 * New commands

 set exec-file-mismatch -- Set exec-file-mismatch handling (ask|warn|off).

Re: [PATCH v2 1/2] Display ExceptionRecord for $_siginfo

[Eli Zaretskii]

> Date: Sat, 8 Feb 2020 21:09:21 +0000 (UTC)
> From: "Hannes Domani via gdb-patches" <gdb-patches@sourceware.org>
> 
> Is it fine if I add the following to this patch?:
> 
>     * NEWS: Mention $_siginfo support for Windows.
> ---
> diff --git a/gdb/NEWS b/gdb/NEWS
> index d4e2e70f38..c202fe06de 100644
> --- a/gdb/NEWS
> +++ b/gdb/NEWS
> @@ -10,6 +10,9 @@
>    that support it (see entry for GDB 9, below), providing faster
>    performance for programs with many symbols.
> 
> +* The $_siginfo convenience variable now also works on Windows targets,
> +  and will display the EXCEPTION_RECORD of the last handled exception.
> +
>  * New commands

Yes, this sounds good to me, thanks.

Re: [PATCH v2 1/2] Display ExceptionRecord for $_siginfo

[Simon Marchi]

On 2020-02-08 10:28 p.m., Eli Zaretskii wrote:
>> Date: Sat, 8 Feb 2020 21:09:21 +0000 (UTC)
>> From: "Hannes Domani via gdb-patches" <gdb-patches@sourceware.org>
>>
>> Is it fine if I add the following to this patch?:
>>
>>     * NEWS: Mention $_siginfo support for Windows.
>> ---
>> diff --git a/gdb/NEWS b/gdb/NEWS
>> index d4e2e70f38..c202fe06de 100644
>> --- a/gdb/NEWS
>> +++ b/gdb/NEWS
>> @@ -10,6 +10,9 @@
>>    that support it (see entry for GDB 9, below), providing faster
>>    performance for programs with many symbols.
>>
>> +* The $_siginfo convenience variable now also works on Windows targets,
>> +  and will display the EXCEPTION_RECORD of the last handled exception.
>> +
>>  * New commands
> 
> Yes, this sounds good to me, thanks.

Thanks for chiming in Eli.

So Hannes, just to be clear, you can go ahead and push this series, thanks!

Simon

Re: [PATCH v2 1/2] Display ExceptionRecord for $_siginfo

[Hannes Domani via gdb-patches]

 Am Sonntag, 9. Februar 2020, 06:33:39 MEZ hat Simon Marchi <simark@simark.ca> Folgendes geschrieben:

> On 2020-02-08 10:28 p.m., Eli Zaretskii wrote:
>
> >> Date: Sat, 8 Feb 2020 21:09:21 +0000 (UTC)
> >> From: "Hannes Domani via gdb-patches" <gdb-patches@sourceware.org>
> >>
> >> Is it fine if I add the following to this patch?:
> >>
> >>     * NEWS: Mention $_siginfo support for Windows.
> >> ---
> >> diff --git a/gdb/NEWS b/gdb/NEWS
> >> index d4e2e70f38..c202fe06de 100644
> >> --- a/gdb/NEWS
> >> +++ b/gdb/NEWS
> >> @@ -10,6 +10,9 @@
> >>    that support it (see entry for GDB 9, below), providing faster
> >>    performance for programs with many symbols.
> >>
> >> +* The $_siginfo convenience variable now also works on Windows targets,
> >> +  and will display the EXCEPTION_RECORD of the last handled exception.
> >> +
> >>  * New commands
> >
> > Yes, this sounds good to me, thanks.
>
>
> Thanks for chiming in Eli.
>
> So Hannes, just to be clear, you can go ahead and push this series, thanks!

Pushed, thanks.