An Explanation of VDMDBG.DLL
BobDay - 10 Jun 93
Section 1.0 - Overview
Section 2.0 - The Simulated Environment
Section 3.0 - The 32-bit Environment
Section 4.0 - Communication Protocol via Exception
Section 5.0 - The VDM Debugging APIs
1.0 Overview
This document describes the mechanism used to support debugging DOS and
WIN16 applications under Windows NT. The mechanism involves 2 parts
in the simulated environment, one for v86 mode (or simulated real mode)
and one for protected mode. It also involves 3 parts in the 32-bit NT
environment, one for fielding information from the simulated enviroment
and sending it to the debugger, one for code in the debugger, and one
for code in a DLL used by the debugger.
16-bit simulated environment 32-bit environment
NTIO.SYS DBG.LIB (in NTVDM.EXE)
KRNL286.EXE NTSD (WinDbg or equivalent)
VDMDBG.DLL
2.0 Simulated enviroment
Once the simulated environment is up and running, if one of the normal
debugging type events occurs it gets simulated to happen exactly the
way it would on a normal PC. This means that if an INT 3 occurs, it
pushes the flags, CS, IP, looks up the address in the IVT and then
jumps to it. Same goes for INT 1's and INT D's (GP Faults). If the
processor is in protected mode, these interrupts are normally trapped
by the DOS extender (most of the time DOSX.EXE) and then reflected
down into the real mode interrupts (except for GP Faults).
In order to debug in the simulated enviroment, it is necessary to
catch and process these events. The simplest way to do this is to
install our own routines to watch these interrupts and that is
what NTIO.SYS and KRNL286.EXE do. They are nothing but small
stubs which insert themselves into the interrupt chains (NTIO.SYS
inserts itself into the real mode interrupt chain, and KRNL286.EXE
inserts itself into the protected mode interrupt chain). It is important
to install oneself as early as possible so that other programs (such
as DEBUG.COM) can install themselves ahead of these small stubs.
In this way the events are only detected when they are not handled by some
program in the simulated environment.
Also, segment loading and unloading notifications are routed to
these small stubs so that the debugger can be notified when selectors
are associated with programs and their symbols.
The small stubs will perform a BOP (a method of transitioning from
the simulated environment back to the real 32-bit NT environment and
notifying it that a debug event has occurred). After the BOP, they will
either perform an IRET instruction to return control back to the simulated
program generating the interrupt, or pass the interrupt down to the
previous interrupt handler (continue down the chain). The decision
whether to return from or pass the interrupt will be made on the basis
of the ContinueDebugEvent continue status parameter. DBG_CONTINUE will
IRET, DBG_EXCEPTION_NOT_HANDLE will pass it back down the chain.
3.0 32-bit environment
Once the 32-bit environment has been notified that a debug event has
occurred, it begins executing code in NTVDM (DBG.C) which parcels up the
register context (based on the type of event which occurred) and
communicates all the information to the debugger.
Since the debugger is in another process's context, communication
is done through exceptions. NTVDM will raise an exception with the
status STATUS_VDM_EVENT. Exception information will be passed via the
"lpArguments" parameter to the API RaiseException().
The lpArguments parameter will cause an array of 4 DWORD values to
be passed to the debugger. The values of the meanings of the array
will be discussed in section 4.0
The debugger should receive this exception and return from the call
WaitForDebugEvent (debuggers should always have some thread waiting
for debug events). By examining the events dwDebugEventCode member,
the debugger can determine the type of the debug event. If this type
is EXCEPTION_DEBUG_EVENT, then the
u.Exception.ExceptionRecord.ExceptionCode
member of the debug event structure will contain the exception type.
If this value is STATUS_VDM_EVENT then the exception is coming from the
16-bit environment.
When an exception of this type is detected, a debugger should load (if
it hasn't done so already) the VDMDBG.DLL and determine the addresses
of the key functions needed. The key functions are:
VDMProcessException
VDMGetThreadSelectorEntry
VDMGetPointer
VDMGetThreadContext
VDMSetThreadContext
VDMGetSelectorModule
VDMGetModuleSelector
VDMKillWOW
VDMDetectWOW
VDMBreakThread
VDMModuleFirst
VDMModuleNext
VDMGlobalFirst
VDMGlobalNext
The prototypes and structures used by this DLL are prototyped in the header
file VDMDBG.H. Section 5.0 explains each of these functions.
Debuggers should not use these APIs to deal with the 16-bit environment:
GetThreadSelectoryEntry
GetThreadContext
SetThreadContext
The APIs ReadProcessMemory and WriteProcessMemory are still useful except
that the debugger must convert the 16-bit addresses into 32-bit addresses
(using VDMGetPointer).
Each and every exception with the exception code of STATUS_VDM_EVENT
should be passed to the function VDMProcessException. This function
filters out the extraneous communication between the 16-bit environment
and the VDMDBG.DLL. Most of this extraneous communication a debugger
can ignore (deals with segment & module loading & unloading, this
information will be provided via another interface). If the event is
part of this communication process, VDMProcessException will return
FALSE, if not, it will return TRUE.
If the function VDMProcessException returns FALSE, the debugger can
immediately call the API ContinueDebugEvent with a continue status of
DBG_CONTINUE and return to waiting for additional debug events.
If the function VDMProcessException returns TRUE, then the lpArguments
parameter of the exception should be processed to determine the type of
event (INT 1, INT 3, INT D, etc.). The debugger can then act accordingly.
When it has completed operating with the thread, the debugger should
call the API ContinueDebugEvent with a continue status of DBG_CONTINUE
or DBG_EXCEPTION_NOT_HANDLED.
For the processing of each of the debug events, the debugger should use
the API VDMGetThreadSelectorEntry, VDMGetThreadContext, and
VDMSetThreadContext instead of the likewise named functions listed above
that are exported from KERNEL32.DLL. These functions operate on an x86
CONTEXT structure, even when running on a non-x86 machine. The debugger
should likewise present an x86 debugging view (x86 register dump, x86
dis-assembly, breakpoints are INT 3's, etc.)
4.0 Communication Protocol via. Exceptions
The method of communicating between the application and debugger
will be exceptions. NTVDM will raise an exception and debugger should
receive it. NTVDM can detect whether or not it is being debugged, and
will conditionally raise the exception.
If a debugger attaches itself to an existing NTVDM process, the
32-bit environment detects this and comminicates an acknowledgement
of this attachment. This allows debuggers to perform initialization
dealing with the 16-bit environment before beginning any new 16-bit tasks.
For the simulated 16-bit environment, the exception code will always be
STATUS_VDM_EVENT.
On NT, each exception can only contain up to 4 DWORD values. Here is
how they are used for this communication. The first 2 DWORDs contain
4 WORD fields. The last two DWORDs are just DWORDs.
+---------+
| W1 | W2 | = DW1
+---------+
| W3 | W4 | = DW2
+---------+
| DW3 |
+---------+
| DW4 |
+---------+
The header file VDMDBG.H contains macros for isolating the individual
parts of the exception information.
The W1 field is a WORD which specifies which type of event has occurred.
This can be one of the following:
W1 == 0 - Segment Load Notification (DBG_SEGLOAD)
W1 == 1 - Segment Move Notification (DBG_SEGMOVE)
W1 == 2 - Segment Free Notification (DBG_SEGFREE)
W1 == 3 - Module Load Notification (DBG_MODLOAD)
W1 == 4 - Module Free Notification (DBG_MODFREE)
W1 == 5 - Int 01h break (DBG_SINGLESTEP)
W1 == 6 - Int 03h break (DBG_BREAKPOINT)
W1 == 7 - Int 0Dh break (GP Fault) (DBG_GPFAULT)
W1 == 8 - Divide Overflow (DBG_DIVOVERFLOW)
W1 == 9 - Invalid Opcode Fault (DBG_INSTRFAULT)
W1 == 10 - Task starting (DBG_TASKSTART)
W1 == 11 - Task stop (DBG_TASKSTOP)
W1 == 12 - DLL starting (DBG_DLLSTART)
W1 == 13 - DLL stop (DBG_DLLSTOP)
They are described below.
The debugger will probably need to be smart enough to know how to manage
both protected mode selectors and segment numbers from simulated real mode.
Segment/selector to symbol lookup should be mode sensitive and only use
segments from the appropriate mode.
4.1 Segment Load Notification
Under Win16, this event is used to indicate that a selector has just
been created and that it maps to a module's segment.
When a .EXE or .DLL is loaded, many of these events will be received.
No module load notification event will occur (this is the way it is
done under Windows 3.1 too).
Under DOS, no segment load notifications will occur.
W1 = DBG_SEGLOAD (0)
W2 = Unused
W3 = Unused
W4 = Unused
DW3 = Pointer to a SEGMENT_NOTE structure in NTVDM address space
DW4 = Reserved
SEGMENT_NOTE structure field definitions will be:
Selector1 - Selector assigned to new segment
Selector2 - Unused
Segment - Segment within module
Module - Null terminated module name
FileName - Null terminated path to executable image
Type - Code/data information from segment definition
Length - Unused
VDMProcessException will return FALSE for this event.
4.2 Segment Move Notification
A segment has changed from one selector number to another. If the
new selector number is 0, this should be considered the same as
discarding (freeing) the segment.
This event only happens under Win16. As such, these selectors should be
tagged as protected mode only selectors.
W1 = DBG_SEGMOVE (1)
W2 = Unused
W3 = Unused
W4 = Unused
DW3 = Pointer to a SEGMENT_NOTE structure in NTVDM address space
DW4 = Reserved
SEGMENT_NOTE structure field definitions will be:
Selector1 - Old selector number
Selector2 - New selector number (0 to discard segment)
Segment - Unused
Module - Unused
FileName - Unused
Type - Unused
Length - Unused
VDMProcessException will return FALSE for this event.
4.3 Segment Free Notification
When a segment is being released, this event will be received.
This event only happens under Win16.
W1 = DBG_SEGFREE (2)
W2 = Unused
W3 = Unused
W4 = Unused
DW3 = Pointer to a SEGMENT_NOTE structure in NTVDM address space
DW4 = Reserved
SEGMENT_NOTE structure field definitions will be:
Selector1 - Selector number
Selector2 - Unused
Segment - Unused
Module - Unused
FileName - Unused
Type - Unused
Length - Unused
VDMProcessException will return FALSE for this event.
4.4 Module Load Notification
This event is used to indicate that a module is going to take up a
range of memory.
This event is used only under DOS. As such, these segment numbers
should be tagged as simulated real mode only selectors.
W1 = DBG_MODLOAD (3)
W2 = Unused
W3 = Unused
W4 = Unused
DW3 = Pointer to a SEGMENT_NOTE structure in NTVDM address space
DW4 = Reserved
SEGMENT_NOTE structure field definitions will be:
Selector1 - Unused
Selector2 - Unused
Segment - Starting segment
Module - Null terminated module name
FileName - Null terminated path to executable image
Type - Unused
Length - Length of module (in bytes)
VDMProcessException will return FALSE for this event.
4.5 Module Free Notification
Module freeing notifications happen under both DOS and Win16. For
to determine which selectors to free for a Win16 application, all of the
selectors must be scanned to determine if it was associated with this
module. Again, this is the way it is done under Windows 3.1.
W1 = DBG_MODFREE (4)
W2 = Unused
W3 = Unused
W4 = Unused
DW3 = Pointer to a SEGMENT_NOTE structure in NTVDM address space
DW4 = Reserved
SEGMENT_NOTE structure field definitions will be:
Selector1 - Unused
Selector2 - Unused
Segment - Unused
Module - Null terminated module name
FileName - Null terminated path to executable image
Type - Unused
Length - Unused
VDMProcessException will return FALSE for this event.
4.6 Int 01h break
This event probably requires interaction with the debugger and its
internal breakpoint, trace bit setting mechanisms.
W1 = DBG_SINGLE_STEP (5)
W2 = Unused
W3 = Unused
W4 = Unused
DW3 = Unused
DW4 = Reserved
VDMProcessException will return TRUE for this event.
4.7 Int 03h break
This event probably requires interaction with the debugger and its
internal breakpoints.
W1 = DBG_BREAKPOINT (6)
W2 = Unused
W3 = Unused
W4 = Unused
DW3 = Unused
DW4 = Reserved
VDMProcessException will return TRUE for this event.
4.8 Int 0Dh break (GP Fault)
This event probably requires interaction with the debugger and its
internal breakpoints.
W1 = DBG_GPFAULT (7)
W2 = Unused
W3 = Unused
W4 = Unused
DW3 = Unused
DW4 = Reserved
It is also important to note that all GP Faults will not be sent via
this interface. The Win16 subsystem intercepts some of the GP faults
in its parameter validation code. Faults in the parameter validation
code indicated that an invalid parameter is being passed to one of the
16-bit APIs. There is currently no way to intercept these faults, the
APIs will just return errors in the same mechanism as under Windows 3.1.
VDMProcessException will return TRUE for this event.
4.9 Divide Overflow break (Int 0)
This event probably requires interaction with the debugger and its
internal breakpoints.
W1 = DBG_DIVOVERFLOW (8)
W2 = Unused
W3 = Unused
W4 = Unused
DW3 = Unused
DW4 = Reserved
VDMProcessException will return TRUE for this event.
4.A Invalid Opcode Fault (Int 6)
W1 = DBG_INSTRFAULT (9)
W2 = Unused
W3 = Unused
W4 = Unused
DW3 = Unused
DW4 = Reserved
VDMProcessException will return TRUE for this event.
4.B Task starting
After all of the image has been loaded for the application, but
before executing the first instruction, this event will occur.
W1 = DBG_TASKSTART (0Ah)
W2 = Unused
W3 = Unused
W4 = Unused
DW3 = Pointer to an IMAGE_NOTE structure in NTVDM address space
DW4 = Reserved
IMAGE_NOTE structure field definitions will be:
Module - Null terminated module name
FileName - Null terminated path to executable image
VDMProcessException will return TRUE for this event.
4.C Task stopping
After all of the image has been unloaded for the application
this event will occur. None of the segments for the application
will be valid. This is provided for the debugger to clean up any
internal data it keeps on a per task basis.
W1 = DBG_TASKSTOP (0Bh)
W2 = Unused
W3 = Unused
W4 = Unused
DW3 = Pointer to an IMAGE_NOTE structure in NTVDM address space
DW4 = Reserved
IMAGE_NOTE structure field definitions will be:
Module - Null terminated module name
FileName - Null terminated path to executable image
VDMProcessException will return TRUE for this event.
4.D Dll starting
After the image of the DLL has been loaded, but before the
Dll's initialization code is executed, this event will occur.
W1 = DBG_DLLSTART (0Ch)
W2 = Unused
W3 = Unused
W4 = Unused
DW3 = Pointer to an IMAGE_NOTE structure in NTVDM address space
DW4 = Reserved
IMAGE_NOTE structure field definitions will be:
Module - Null terminated module name
FileName - Null terminated path to executable image
VDMProcessException will return TRUE for this event.
4.E Dll stopping
After all of the image of the DLL has been unloaded for the Dll
this event will occur. None of the segments for the Dll will be
valid. This is provided for the debugger to clean up any internal
data it keeps on a per Dll basis.
W1 = DBG_DLLSTOP (0Ch)
W2 = Unused
W3 = Unused
W4 = Unused
DW3 = Pointer to an IMAGE_NOTE structure in NTVDM address space
DW4 = Reserved
IMAGE_NOTE structure field definitions will be:
Module - Null terminated module name
FileName - Null terminated path to executable image
VDMProcessException will return TRUE for this event.
4.F Attach Acknowlegement
Once the 16-bit environment has detected that a debugger is present
it sends this event to allow the debugger to perform any initialization
processing specific to the 16-bit environment.
W1 = DBG_ATTACH (0Dh)
W2 = Unused
W3 = Unused
W4 = Unused
DW3 = Unused
DW4 = Reserved
VDMProcessException will return TRUE for this event.
5.0 The VDM debugging APIs
These APIs are described below:
VDMProcessException
VDMGetThreadSelectorEntry
VDMGetPointer
VDMGetThreadContext
VDMSetThreadContext
VDMGetSelectorModule
VDMGetModuleSelector
VDMEnumProcessWOW
VDMEnumTaskWOW
The following APIs require WOWDEB.EXE to be loaded and running in the
Win16 subsystem. WOWDEB.EXE is started automatically if the debugger
is present at process creation time (CreateProcess with debug options
set). If the debugger is attached to the Win16 subsystem process after
the process has already been created (with the DebugActiveProcess API),
then the debugger should spawn WOWDEB.EXE before starting the Win16 task
to be debugged.
VDMModuleFirst
VDMModuleNext
VDMGlobalFirst
VDMGlobalNext
This following APIs are obsolete. They return failure conditions.
VDMKillWOW
VDMDetectWOW
VDMBreakThread
5.1 VDMProcessException
BOOL VDMProcessException(
LPDEBUG_EVENT lpDebugEvent
);
The VDMProcessExecption function performs the pre-processing needed to
prepare the debug event for handling by the debugger.
This function filters all VDM debugee/debugger communication for
information which is only used by the VDM debugging DLL (VDMDBG.DLL).
This function is only valid in the context of processing for debug
events that are of type STATUS_VDM_EVENT.
lpDebugEvent Points to a DEBUG_EVENT structure that was returned
from WaitForDebugEvent.
The return value is TRUE if the debug event should be processed by the
debugger.
The return value is FALSE if the debug event should be ignored. This
This indicates that no processing should occur for this debug event.
The event should be continued using ContinueDebugEvent with a continue
status of DBG_CONTINUE.
5.2 VDMGetThreadSelectorEntry
BOOL VDMGetThreadSelectorEntry(
HANDLE hProcess,
HANDLE hThread,
WORD wSelector
LPLDT_ENTRY lpSelectorEntry
);
This function is used to return a descriptor table entry for the
specified VDM thread corresponding to the specified selector. This
function is simimlar to the API GetThreadSelectorEntry except that
it works on the simulated DOS/WIN16 environment, and it works on all
systems, not just x86 systems.
This API returns a simulated descriptor entry on non-x86 systems.
Simulated descriptor entrys may (on some systems) have the base value
adjusted to account for the fact that the simulated address space may
not begin at linear (32-bit) address 0.
It is also important to note that 16-bit applications may modify
the contents of the LDT entries. For example, the Win16 subsystem
may change the selector's base value to coalesce discontinous memory
segments. Also, please see the description in VDMGetPointer.
hProcess Supplies a handle to the DOS/WIN16 sub-system process.
The handle must have been created with PROCESS_VM_READ
access.
hThread Supplies a handle to the thread that contains the
specified selector. The handle must have been created
with THREAD_QUERY_INFORMATION access.
wSelector Supplies the selector value to look up. The selector
value may be a global selector (GDT) or a local selector
(LDT).
lpSelectorEntry If the specifed selector is contained within the
thread's descriptor tables, its descriptor table entry
is copied into the data structure pointed to by this
parameter. This data can be used to compute the linear
base address that segment relative addresses refer to.
The return value is TRUE if the operation was successful. In that case,
the data structure pointed to by lpSelectorEntry receives a copy of the
specified descriptor table entry.
Refer to the WinHelp entry for the structure of an LDT_ENTRY.
5.3 VDMGetPointer
ULONG VDMGetPointer(
HANDLE hProcess,
HANDLE hThread,
WORD wSelector,
DWORD dwOffset,
BOOL fProtMode
);
This function is used to convert a 16-bit address into a flat 32-bit
address.
It is also very important to note that under the WIN16 environment,
pointers derived from protected mode selectors may change. WIN16 does
this by changing selector's base value to coalesce memory during
compaction. For this reason, it is necessary that any addresses
evaluated in the 16-bit environment should be reevaluated each time
an access into 16-bit memory is needed. An example would be
placing and removing 16-bit breakpoint instructions. If the debugger
is told to place a breakpoint at a given address of SEL:OFFSET, then
when the breakpoint is needs to be removed, the debugger must reevaluate
the SEL:OFFSET address since it might have moved in terms of the linear
32-bit address.
hProcess Supplies a handle to the DOS/WIN16 sub-system process.
The handle must have been created with PROCESS_VM_READ
access.
hThread Supplies a handle to the thread that contains the
specified selector. The handle must have been created
with THREAD_QUERY_INFORMATION access.
wSelector Supplies the selector value to determine the pointer for.
dwOffset Supplies the offset value to determine the pointer for.
fProtMode Indicates whether the 16-bit address specified is a
real mode (v86 mode) address or a protected mode address.
Protected mode addresses are translated through the
descriptor tables.
The return value is a 32-bit linear address pointing to the memory
in the simulated DOS/WIN16 environment that represents the 16-bit address
specified. The return value is NULL, if the address specified is invalid.
On some systems, NULL may be returned for the address 0:0.
To determine the address of the simulated 16-bit memory, VDMGetPointer
may be called with the address 0:0 and an fProtMode of FALSE.
5.4 VDMGetThreadContext
BOOL VDMGetThreadContext(
LPDEBUG_EVENT lpDebugEvent,
LPVDMCONTEXT lpVDMContext
);
The context of a specified simulated DOS or WIN16 thread can be
retrieved using VDMGetThreadContext. The context returned will
always be that of an x86 system.
This API returns a simulated context for x86 and non-x86 systems.
Under some systems, values within the context are meaningless. For
example, the CONTEXT_DEBUG_REGISTERS portions on RISC systems have
no effect.
Release 1 of Windows NT has a 286 emulator on RISC systems. For this
reason, only the 16-bit registers can be supported on RISC systems.
lpDebugEvent Points to a DEBUG_EVENT structure that was returned
from WaitForDebugEvent.
lpVDMContext If the specified thread is a simulated DOS or WIN16
thread, its context is copied into the data structure
pointed to by this parameter.
The return value is TRUE if the operation was successful. In that case,
the data structure pointed to by <lpVDMContext> receives a copy of the
simulated context.
Refer to the WinHelp for the structure of a VDMCONTEXT (same as x86
CONTEXT structure in NTI386.H).
5.5 VDMSetThreadContext
BOOL VDMSetThreadContext(
LPDEBUG_EVENT lpDebugEvent,
LPVDMCONTEXT lpVDMContext
);
The VDMSetThreadContext function sets the simulated context in the
specified DOS or WIN16 thread. The function allows selective context
to be set based on the value of the ContextFlags member of the context
structure. This API operates only when debugging a simulated DOS or
WIN16 thread. The caller must have a thread handle which was created
with THREAD_SET_CONTEXT access.
The context set will always be that of an x86 system.
lpDebugEvent Points to a DEBUG_EVENT structure that was returned
from WaitForDebugEvent.
lpVDMContext Supplies the address of a context structure that
contains the context that is to be set in the specified
thread. The value of the ContextFlags member of this
structure specifies which portions of a thread's context
are to be set. Some values in the context structure are
not settable and are silently set to the correct values.
This include CPU status register bits that specify
processor mode, debug register global enabling bits, and
other state that must be completely controlled by the
system.
The return value is TRUE if the context was set; otherwise it is FALSE if
an error occurred.
Refer to the WinHelp for the structure of a VDMCONTEXT (same as x86
CONTEXT structure in NTI386.H).
5.6 VDMGetSelectorModule
BOOL VDMGetSelectorModule(
HANDLE hProcess,
HANDLE hThread,
WORD wSelector,
PUINT lpSegmentNumber,
LPSTR lpModuleName,
UINT nSize,
LPSTR lpModulePath,
UINT nPathSize
);
The VDMGetSelectorModule function is intended to provide an interface
such that debuggers can determine which module belongs to a code or
data address. Given the selector for that address, the function will
return the module name, and the segment number (0 based) of the segment
that corresponds to that selector. If the selector is not a selector
which directly corresponds to a module, the function will return FALSE.
hProcess Supplies a handle to the process of the 16-bit environment
hThread Supplies a handle to a thread in the 16-bit environment
wSelector Supplies the selector value to look up.
lpSegmentNumber Returns the segment number within the module.
lpModuleName Buffer to receive the module name.
nModuleSize Size of the buffer.
lpModulePath Buffer to receive the module path name.
nPathSize Size of the buffer.
The return value is TRUE if the selector is mapped directly to a module.
This means it must be either a code or data segment. Selectors allocated
using the global memory management functions are not mapped directly to
a module. The return value is FALSE if the function is not successful.
The function returns the segment number in the address specified by
the lpSegmentNumber parameter, and the module name in the address
specified by the lpModuleName parameter.
It is up to the debugger to determine from the module and segment number
information the correct symbol, if a symbol lookup is needed.
5.7 VDMGetModuleSelector
BOOL VDMGetModuleSelector(
HANDLE hProcess,
HANDLE hThread,
UINT uSegmentNumber,
LPSTR lpModuleName,
LPWORD lpSelector
);
The VDMGetModuleSelector function is the reverse operation of the
VDMGetSelectorModule function. A module name and segment number
are converted into a selector number.
hProcess Supplies a handle to the process of the 16-bit environment
hThread Supplies a handle to a thread in the 16-bit environment
uSegmentNumber Supplies the segment number to look up.
lpModuleName Specifies the module name of the segment.
lpSelector Returns the selector value.
The return value is TRUE if the module and segment are found. Also,
the lpSelector value is filled-in with the selector of that segment.
Otherwise, the return value is FALSE.
It is up to the debugger to convert symbol names and expressions into
modules, segment numbers and offsets. Usings the modules and segment
numbers, a selector value can be determined. In combination with the
offset, the selector can be used to index into the simulated Win16
environment for reading, writing, etc.
5.8 VDMEnumProcessWOW
INT VDMEnumProcessWOW(
PROCESSENUMPROC fp,
LPARAM lparam
);
The VDMEnumProcessWOW function enumerates all of the processes in
the system which are Win16 subsystem processes. In NT's first release,
there is only one Win16 subsystem. For later releases, there may be
more than one process to support address space seperation for Win16
tasks.
fp Supplies the address of a callback routine.
lparam Supplies a parameter to the callback routine.
The return value is the number of Win16 subsystem processes, or the
number enumerated before enumeration was terminated.
BOOL ProcessEnumProc(
DWORD dwProcessId,
DWORD dwAttributes,
LPARAM lparam
);
The callback function will be called once for each Win16 subsystem process
in the system.
dwProcessId Provides the process id of a Win16 subsystem.
dwAttributes Provides flags indicating information about the process.
lparam Provides the parameter passed to VDMEnumProcessWOW
The callback function should return a non-zero value to terminate
enumeration.
The dwAttributes field should be compared with the bit mask WOW_SYSTEM
to determine if the process is the main Win16 subsystem process. The
main Win16 subsystem process will be the process that the next Win16
task that specifies no address space seperation requirements.
Win16 subsystem processes which are created due to address space
seperation will not have the WOW_SYSTEM bit enabled.
5.9 VDMEnumTaskWOW
INT
VDMEnumTaskWOW(
DWORD dwProcessId,
TASKENUMPROC fp,
LPARAM lparam
);
The VDMEnumTaskWOW function enumerates all of the Win16 tasks currently
running in the Win16 subsystem process id specified.
dwProcessId Supplies the process id of the Win16 subsystem.
fp Supplies the address of a callback routine.
lparam Supplies a parameter to the callback routine.
The return value is the number of Win16 tasks or the number of
tasks enumerated before terminating.
BOOL TaskEnumProc(
DWORD dwThreadId,
WORD hMod16,
WORD hTask16,
LPARAM lparam
);
The callback function will be called once for each Win16 task.
dwThreadId Provides the thread id of the Win16 task
hMod16 Provides the Win16 module handle for the task
hTask16 Provides the Win16 task handle for the task
lparam Provides the parameter passed to VDMEnumTaskWOW
The callback function should return a non-zero value to terminate
enumeration.
5.A VDMModuleFirst
BOOL VDMModuleFirst(
HANDLE hProcess,
HANDLE hThread,
LPMODULEENTRY lpModuleEntry,
DEBUGEVENTPROC lpEventProc,
LPVOID lpData
);
This function is used to start enumerating all of the modules currently
loaded in the 16-bit Windows environment. It behaves in the same manner
as the Windows 3.1 ToolHelp API ModuleFirst().
hProcess Supplies a handle to the process of the 16-bit environment
hThread Supplies a handle to a thread in the 16-bit environment
lpModuleEntry Specifies the address of a MODULEENTRY structure which
will be filled in with the first module in the module
list.
lpEventProc Specifies the address of a procedure which might be
called in the event of a debug event occuring while
the communication session with the 16-bit enviroment
is occurring.
lpData Specifies a parameter to pass to the debug event procudure
The return value is TRUE if the operation was successful. In that case,
the MODULEENTRY structure will be filled in with information for the
first module in the module list.
5.B VDMModuleNext
BOOL VDMModuleNext(
HANDLE hProcess,
HANDLE hThread,
LPMODULEENTRY lpModuleEntry,
DEBUGEVENTPROC lpEventProc,
LPVOID lpData
);
This function is used to continue enumerating all of the modules currently
loaded in the 16-bit Windows environment. It behaves in the same manner
as the Windows 3.1 ToolHelp API ModuleNext().
hProcess Supplies a handle to the process of the 16-bit environment
hThread Supplies a handle to a thread in the 16-bit environment
lpModuleEntry Specifies the address of a MODULEENTRY structure which
will be used to determine the next module and which will
be filled in with the next module in the module list.
lpEventProc Specifies the address of a procedure which might be
called in the event of a debug event occuring while
the communication session with the 16-bit enviroment
is occurring.
lpData Specifies a parameter to pass to the debug event procudure
The return value is TRUE if the operation was successful. In that case,
the MODULEENTRY structure will be filled in with information for the
next module in the module list.
5.C VDMGlobalFirst
BOOL VDMGlobalFirst(
HANDLE hProcess,
HANDLE hThread,
LPGLOBALENTRY lpGlobalEntry,
WORD wFlags,
DEBUGEVENTPROC lpEventProc,
LPVOID lpData
);
This function is used to continue enumerating all of the global memory
blocks currently allocated in the 16-bit Windows environment. It
behaves in the same manner as the Windows 3.1 ToolHelp API GlobalFirst().
hProcess Supplies a handle to the process of the 16-bit environment
hThread Supplies a handle to a thread in the 16-bit environment
lpModuleEntry Specifies the address of a GLOBALENTRY structure which
will be filled in with information for the first global
memory block matching the specified flags
wFlags Specifies which types of global memory blocks to enumerate
lpEventProc Specifies the address of a procedure which might be
called in the event of a debug event occuring while
the communication session with the 16-bit enviroment
is occurring.
lpData Specifies a parameter to pass to the debug event procudure
The return value is TRUE if the operation was successful. In that case,
the GLOBALENTRY structure will be filled in with information for the
first global memory block that matches the specified flags.
5.D VDMGlobalNext
BOOL VDMGlobalNext(
HANDLE hProcess,
HANDLE hThread,
LPGLOBALENTRY lpGlobalEntry,
WORD wFlags,
DEBUGEVENTPROC lpEventProc,
LPVOID lpData
);
This function is used to continue enumerating all of the global memory
blocks currently allocated in the 16-bit Windows environment. It behaves
in the same manner as the Windows 3.1 ToolHelp API GlobalNext().
hProcess Supplies a handle to the process of the 16-bit environment
hThread Supplies a handle to a thread in the 16-bit environment
lpModuleEntry Specifies the address of a GLOBALENTRY structure which
will be used to determine the next global memory block
and which will be filled in with information for the
next global memory block matching the specified flags
wFlags Specifies which types of global memory blocks to enumerate
lpEventProc Specifies the address of a procedure which might be
called in the event of a debug event occuring while
the communication session with the 16-bit enviroment
is occurring.
lpData Specifies a parameter to pass to the debug event procudure
The return value is TRUE if the operation was successful. In that case,
the GLOBALENTRY structure will be filled in with information for the
next global memory block that matches the specified flags.
5.E VDMKillWOW
BOOL VDMKillWOW(void);
This function is obsolete and performs no operation. It returns FALSE.
5.F VDMDetectWOW
BOOL VDMDetectWOW(void);
This function is obsolete and performs no operation. It returns FALSE.
5.G VDMBreakThread
BOOL VDMBreakThread(
HANDLE hProcess
HANDLE hThread
);
This function is obsolete and performs no operation. It returns FALSE.
