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

[Ryan Johnson]

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.

With handle SIGTSTP nostop noprint pass, gdb doesn't break in any more, 
but both gdb and the victim still hang on ^Z. This time, killing gdb 
also silently kills the app, with the shell reporting exit code 0 and no 
job completion notice (presumably because the victim didn't finish 
backgrounding itself before being killed).

Running under linux/gdb, the STC behaves as expected, breaking in after 
the shell reports that the victim has backgrounded. You'd want to nostop 
SIGTSTP, SIGTTIN and SIGCONT to keep the debugger from getting 
underfoot, though.

(changing the subject line to reflect the new issue, since it's probably 
not directly related to the original problem)

[1] BTW, did you intend for a gdb release announcement to go out? None 
came that I can see, though the mirrors seem to have picked it up.
[2] As usual, gdb only breaks in response to ^C if you invoke it 
directly from cmd.exe, but the above hang causes it to ignore ^C even then.

Ryan


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