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Message-ID: <51F91C84.3020809@cs.utoronto.ca>
Date: Wed, 31 Jul 2013 10:17:40 -0400
From: Ryan Johnson <ryan.johnson@cs.utoronto.ca>
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To: cygwin@cygwin.com
Subject: Re: gdb hangs on ^Z [was: Re: 64-bit gdb: invalid decimal " 0x22DBF0"]
References: <51F33E9D.9030703@cs.utoronto.ca> <51F3A133.8090805@star.sr.bham.ac.uk> <20130729110626.GB30069@calimero.vinschen.de> <51F691D2.205@cs.utoronto.ca> <20130729191118.GG4166@calimero.vinschen.de> <51F6BEF0.10003@cs.utoronto.ca> <51F6C22D.70708@cs.utoronto.ca>
In-Reply-To: <51F6C22D.70708@cs.utoronto.ca>
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On 29/07/2013 3:27 PM, Ryan Johnson wrote:
> On 29/07/2013 3:13 PM, Ryan Johnson wrote:
>> On 29/07/2013 3:11 PM, Corinna Vinschen wrote:
>>> On Jul 29 12:01, Ryan Johnson wrote:
>>>> On 29/07/2013 7:06 AM, Corinna Vinschen wrote:
>>>>> On Jul 27 11:30, Daniel Brown wrote:
>>>>>> I have also ran into this problem, in my case though I have managed
>>>>>> to reduce the issue down to an fgets call when reading a pipe.
>>>>>> The following code causes the issue for me if I try and debug it:
>>>>>>
>>>>>> #include <stdio.h>
>>>>>> #include <stdlib.h>
>>>>>>
>>>>>> int main(int argc, char** argv) {
>>>>>>      char out[100] = {0};
>>>>>>      FILE *pipe;
>>>>>>
>>>>>>      if ((pipe = popen("uname -r", "rt")) == NULL)
>>>>>>          fprintf(stderr,"Failed to execute popen command");
>>>>>>
>>>>>>      if(fgets(out, 100, pipe) == NULL)
>>>>>>          fprintf(stderr,"Failed to read popen buffer");
>>>>>>
>>>>>>      printf("%s\n", out);
>>>>>>
>>>>>>      pclose(pipe);
>>>>>>
>>>>>>      return (EXIT_SUCCESS);
>>>>>> }
>>>>>>
>>>>>> I compile with `gcc -g main.c` then `gdb a.exe` and type `run`, the
>>>>>> error `invalid decimal " 0x23DBF0"` then pops up.
>>>>>> I have tried the latest snapshot cygwin1.dll (1.7.23s(0.268/5/3))
>>>>>> and the error is still there.
>>>>> This is a problem in GDB, not in the Cygwin DLL.  My mistake.  I 
>>>>> fetched
>>>>> the official 7.6 version of GDB since it already contained Cygwin 
>>>>> x86_64
>>>>> support so I thought it's sufficient.  Unfortunately it doesn't 
>>>>> handle
>>>>> special Cygwin strings in terms of Cygwin signal handling correctly.
>>>>>
>>>>> I'm just uploading a gdb-7.6.50 version build from current CVS which
>>>>> should fix this.
>>>> Confirmed that this problem is fixed [1]... however, my original STC
>>>> still hangs because gdb somehow interferes with the choreography of
>>>> SIGTSTP between victim and its owning shell.
>>>>
>>>> With default signal handling (SIGTSTP stop print pass) gdb breaks in
>>>> when the victim receives ^Z, but both gdb and the victim hang once
>>>> gdb continues; gdb cannot be interrupted with ^C [2]. Killing gdb
>>>> allows the victim to finish backgrounding itself, apparently none
>>>> the worse for wear.
>>> I'm not sure if ^Z can reliably work in the GDB scenario. That's
>>> Chris' domain, but AFAICS, the fact that GDB calls the inferior
>>> process with CreateProcess, the job control facility of the shell
>>> will be broken.
>> I'm talking about the case where gdb attaches to a running 
>> proccess... I don't know how you could ever handle ^Z in a process 
>> gdb started.
> Just to be extra clear, the scenario is:
> 1. start STC in terminal A
> 2. start gdb in terminal B and attach it to the STC
> 3. type ^Z in terminal A
Is there something I can do to help move this along? It's making it hard 
to debug the sporadic emacs crashes I've been getting (turns out the 
same thing happens for SIGINT, so avoiding the temptation to hit ^Z 
isn't enough).

Thanks
>> Ryan
>
>
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