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Date:	Mon, 20 Oct 2014 15:58:28 -0400
From:	Ken Brown <kbrown AT cornell DOT edu>
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To:	cygwin AT cygwin DOT com
Subject:	Re: Threads
References:	<54450835 DOT 3050602 AT cornell DOT edu> <20141020164324 DOT GA32374 AT calimero DOT vinschen DOT de> <20141020190350 DOT GB32374 AT calimero DOT vinschen DOT de>
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On 10/20/2014 3:03 PM, Corinna Vinschen wrote:
> On Oct 20 18:43, Corinna Vinschen wrote:
>> On Oct 20 09:03, Ken Brown wrote:
>>> When trying to debug emacs in gdb, I see several threads, but it's not
>>> always clear who created those threads and what they're doing.  As an
>>> example, I attached gdb to an emacs-X11 process (running under X) shortly
>>> after starting it, and I obtained the backtrace appended at the end of this
>>> message.
>>>
>>> I assume Thread 12 was created by gdb.
>> [...]
>>> I don't
>>> have any idea where the other threads came from.  Presumably at least one of
>>> them was created by Glib.
>>>
>>> The situation is similar with emacs-w32 and emacs-nox, but with fewer threads.
>>>
>>> In general, is there a way I can understand where all the threads come from?
>>
>> There's no simple generic way to do that, afaik.
>>
>> One big problem is to have all the symbols.  You should definitely
>> install the debuginfo packages of all potentially affected packages, not
>> only cygwin-debuginfo.  If you want to find out where threads are called
>> from the application, you might get a clue by running emacs under GDB and
>> set a breakpoint to pthread_create.
>
> Btw., I don't know if that helps, but the function names of native
> Windows functions given in the GDB backtrace may be off because GDB
> doesn't have access to the Windows DLL symbol tables.  If you want to
> analyze the stacks from that side, you should install WinDbg(*) and the
> symbol files for your OS(**).  If you start the process from WinDbg, you
> can better see the Windows functions called from these threads, while
> not getting any info about the functions from inside the application
> or the Cygwin DLLs.

Thanks, I'll give that a try.

> One of the headaches when porting is sometimes the ABI.  While on Linux
> the first 6 arguments to a function are given in registers, on Windows
> only 4 args are in registers.  This can result in bugs when calling
> functions with more than 4 parameters, which are invisible on Linux, due
> to the way 32 bit parameter are stored in registers on x86_64.  This
> happened to us already for at least one package.

Am I right in thinking this can only be an issue if the source includes 
assembler code?

Ken

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