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gdb "attach" and sharing thread info between processes
- To: email@example.com
- Subject: gdb "attach" and sharing thread info between processes
- From: Egor Duda <firstname.lastname@example.org>
- Date: Thu, 29 Apr 1999 20:36:49 +0400
- Organization: DEO
- Reply-To: Egor Duda <email@example.com>
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"?
Egor. mailto:firstname.lastname@example.org ICQ 5165414 FidoNet 2:5020/496.19