[Qemu-devel] [Bug 1031920] Re: Linux user gdbserver does not respond to remote `Ctrl-C' interrupts

[thierry bultel]

I have encountered that issue recently, and started some analysis.

The issue is due to  the fact that in qemu, gdbstub no longer reads the 
communication channel once
the debugged process is resumed with "cont".
Another way to say that, is that communication with gdb is only possible once 
the process thread execution
is re-routed in the gdb handler.

I am working on a fix.

The fix will consist in having an additional thread, launched that the internal 
gdbserver startup, 
that will be wakeup when the debugged process is resumed. 
That thread will be waiting on the communication channel for the eventually 
incoming CTRL-C request (0x3)
I start to have promising results but it still needs some testing.

Meanwhile, (this should likely be a separate discussion thread, but is somehow 
related with the named issue above)  ,
I also noticed that with multithreaded 
processes, a breakpoint does not suspend all the threads when it is hit. 
This is a little bit annoying, and does not match the expected behaviour that 
is typically seen on a pure native gdb debugging
session.

Once it is ready I will post a patch to qemu mailing list

Best regards
Thierry

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https://bugs.launchpad.net/bugs/1031920

Title:
  Linux user gdbserver does not respond to remote  `Ctrl-C' interrupts

Status in QEMU:
  New

Bug description:
  The bug was reproduced in a recent mainline build for ARM Linux by
  starting emulation with a gdbserver:

  $ qemu-arm -g 1234 a.out

  and then connecting from gdb:

  (gdb) target remote :1234
  Remote debugging using :1234
  [New Remote target]
  [Switching to Remote target]
  0x00008ba8 in _start ()
  (gdb) b main
  Breakpoint 1 at 0x8cb0: file hello.c, line 5.
  (gdb) cont
  Continuing.

  Breakpoint 1, main (argc=1, argv=0xf6fff24c) at hello.c:5
  5       int n = 0;
  (gdb) l
  1     #include <stdio.h>
  2
  3     int main (int argc, char **argv)
  4     {
  5       int n = 0;
  6
  7       for (;;) {
  8          printf ("Hello, World!\n");
  9          sleep (5);
  10      }
  (gdb) cont
  Continuing.
  ^C^CInterrupted while waiting for the program.
  Give up (and stop debugging it)? (y or n) y

  Notice that the `Ctrl-C' interrupts are ignored.

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