[64bit] emacs is unable to call subprocesses if display-time-mode is set

Ken Brown kbrown@cornell.edu
Wed Apr 3 22:02:00 GMT 2013

On 4/3/2013 4:49 PM, Corinna Vinschen wrote:
> On Apr  3 22:02, Corinna Vinschen wrote:
>> On Apr  3 21:03, Corinna Vinschen wrote:
>>> On Apr  3 14:00, Ken Brown wrote:
>>>> On 4/3/2013 10:05 AM, Corinna Vinschen wrote:
>>>>> I can reproduce the issue but it's tricky to debug.  The exception
>>>>> occurs in the forked process and GDB can't follow fork on Cygwin.
>>>>> Btw., can you create an emacs which is built without optimization
>>>>> and non-stripped this would simplify debuigging a bit...
>>>> It was already built without optimization.  I'm working on building
>>>> a non-stripped version, but cygport isn't cooperating.  If you put
>>>> "RESTRICT=strip" into the .cygport file, then cygport doesn't
>>>> package the sources.  So you get a binary with debugging symbols,
>>>> but you don't get the corresponding sources.
>>>> I'll send Yaakov a patch, but in the meantime I'm working around
>>>> this. It shouldn't be long.
>>> I'm still debugging this and something is very fishy when building
>>> the environment for a process-to-exec.  I tracked it down to a
>>> specific string duplication in Cygwin's build_env function which
>>> seems to overwrite administrative data on the cygheap for some
>>> reason I didn't quite follow yet.
>>> This may take some time...
>> I found it.  When using the display-time-mode option, emacs opens and
>> reads /proc/loadavg.  The problem was that the buffer allocated in
>> format_proc_loadavg is too small, so the subsequent sprintf overwrites
>> unrelated data on the cygheap.
>> In fact, this problem occurs on 32 bit as well, so I fixed it in CVS
>> HEAD in the first place.  It's kind of a miracle that this has never
>> been encountered in the 32 bit version before.  The problem exists
>> since at least Cygwin 1.7.10.
>> I'm going to build a new 64 bit Cygwin right now, which I will upload
>> in half an hour or so.  Please give it a try.
> I just uploaded 1.7.18-16 to the 64 bit repo.

The bug is gone.  Thank you!


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