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From: Chris Faylor <cgf AT cygnus DOT com>
Date: Thu, 29 Apr 1999 13:01:22 -0400
To: Egor Duda <deo AT logos-m DOT ru>
Cc: cygwin-developers AT sourceware DOT cygnus DOT com
Subject: Re: gdb "attach" and sharing thread info between processes
Message-ID: <19990429130121.A12386@cygnus.com>
References: <6858 DOT 990429 AT logos-m DOT ru>
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In-Reply-To: <6858.990429@logos-m.ru>; from Egor Duda on Thu, Apr 29, 1999 at 08:36:49PM +0400

The recently announced gdb 4.18 should have the ability to attach to
a running process and manipulate threads.

You can get the sources from
ftp://sourceware.cygnus.com/pub/gdb/releases/gdb-4.18.tar.bz2 .

-chris

On Thu, Apr 29, 1999 at 08:36:49PM +0400, Egor Duda wrote:
>  I've tried to use gdb "attach" feature to debug cygwin program and
>got  INVALID_HANDLE_ERROR in gdb/win32_nat.c. As far, as i see, that's
>due  to  incorrect   value   of   current_process  and  current_thread
>variables. They're  initialized  correctly  when  gdb starts a debugee
>as a child (through CreateProcess call). But when we're "attach"ing to
>some other process,    those    variables   have   wrong   values   :(
>
>  As for `current_process',  this  could  be  easily fixed, by calling
>`OpenProcess'  when attaching to debugee. I've patched win32-nat.c and
>managed    to    watch    vars    from   debugee   (before   patching,
>ReadProcessMemory() fails with INVALID_HANDLE_ERROR.)
>
>  But threads are different  matter...  :(  MS  promise  to  implement
>OpenThread syscall in Win2000 only, and they say, that the only way to
>get  thread  handle  is  to  ask  a  parent process to reveal it. As a
>solution,  i would propose to move threads array (threads var declared
>in  winsup/debug.cc)  from  per-process to shared area and implement a
>call  to  cygwin  dll  to  give  away  thread  handle by processId and
>ThreadId by scanning this thread list.
>
>  With this call gdb will be able to initialize current_thread variable
>properly when attaching to cygwin process.
>
>So, the question is -- is it a "right way"?