gdb hangs on ^Z [was: Re: 64-bit gdb: invalid decimal " 0x22DBF0"]

Ryan Johnson
Mon Jul 29 19:27:00 GMT 2013

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.


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