1 This is a "Simple Windows Debug Server" written for the purpose of

     2 enabling the Serviceability Agent on Win32. It has backends both for

     3 Windows NT 4.0 (using internal Windows APIs for a few routines) as

     4 well as for 95/98/ME/2000 via the Tool Help APIs.

     5 

     6 The reason this debug server is necessary is that the Win32 debug APIs

     7 by design tear down the target process when the debugger exits (see

     8 knowledge base article Q164205 on msdn.microsoft.com). On Solaris, one

     9 can attach to and detach from a process with no effect; this is key to

    10 allowing dbx and gcore to work.

    11 

    12 The Simple Windows Debug Server effectively implements attach/detach

    13 functionality for arbitrary debug clients. This allows the SA to

    14 attach non-destructively to a process, and will enable gcore for Win32

    15 to be written shortly. While the debugger (the "client" in all of the

    16 source code) is attached, the target process is suspended. (Note that

    17 the debug server could be extended to support resumption of the target

    18 process and transmission of debug events over to the debugger, but

    19 this has been left for the future.)

    20 

    21 The makefile (type "nmake") builds two executables: SwDbgSrv.exe,

    22 which is the server process, and SwDbgSub.exe, which is forked by the

    23 server and should not be directly invoked by the user.

    24 

    25 The intent is that these two executables can be installed into

    26 C:\WINNT\SYSTEM32 and SwDbgSrv installed to run as a service (on NT),

    27 for example using ServiceInstaller (http://www.kcmultimedia.com/smaster/). 

    28 However, SwDbgSrv can also be run from the command line. It generates

    29 no text output unless the source code is changed to enable debugging

    30 printouts. As long as any processes which have been attached to by the

    31 SA are alive, the SwDbgSrv and any forked SwDbgSub processes must be

    32 left running. Terminating them will cause termination of the target

    33 processes.

    34 

    35 The debug server opens port 27000 and accepts incoming connections

    36 from localhost only. The security model assumes that if one can run a

    37 process on the given machine then one basically has access to most or

    38 all of the machine's facilities; this seems to be in line with the

    39 standard Windows security model. The protocol used is text-based, so

    40 one can debug the debug server using telnet. See README-commands.txt

    41 for documentation on the supported commands.

    42 

    43 Testing indicates that the performance impact of attaching to a

    44 process (and therefore permanently attaching a debugger) is minimal.

    45 Some serious performance problems had been seen which ultimately

    46 appeared to be a lack of physical memory on the machine running the

    47 system.

    48 

    49 Bugs:

    50 

    51 This debug server is fundamentally incompatible with the Visual C++

    52 debugger. Once the debug server is used to attach to a process, the

    53 Visual C++ IDE will not be able to attach to the same process (even if

    54 the debug server is "detached" from that process). Note that this

    55 system is designed to work with the same primitives that C and C++

    56 debuggers use (like "symbol lookup" and "read from process memory")

    57 and exposes these primitives to Java, so in the long term we could

    58 solve this problem by implementing platform-specific debug symbol

    59 parsing and a platform-independent C++ debugger in Java.

    60 

    61 Note:

    62 

    63 The files IOBuf.cpp and IOBuf.hpp are also used in 

    64 building src/os/solaris/agent.