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Date: Wed, 21 Oct 2009 20:38:14 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: [Qemu-devel] Re: [PATCH] qemu: work around for "posix-aio-compat"
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Mark McLoughlin <markmc@redhat.com>, qemu-devel@nongnu.org


>> At every word of the sigset (using gdb commands to disable/enable the
>> watchpoints around the sigfillset, you avoid spurious triggers).
>
> Not sure how do you mean. When would I enable the watchpoint?

    301  static void *aio_thread(void *unused)
    302  {
    303      pid_t pid;
    304      static sigset_t set;
    305
    306      /* block all signals */
...
    312      if (sigfillset(&set)) die("sigfillset");
....
    315      pid = getpid();
    316
    317      while (1) {


b 312                    // sets bp 1
p ((long *)&set          // prints $1
watch $1[0]              // sets bp 2..9
watch $1[1]
watch $1[2]
watch $1[3]
watch $1[4]
watch $1[5]
watch $1[6]
watch $1[7]              // only 1/4 of the sigset!
                          // stop earlier if it starts
                          // assigning non-hardware watchpoints
                          // try again with 8..15 if not enough
                          // up to $1[31]
commands 1               // don't break on next sigfillset
dis 2
dis 3
dis 4
dis 5
dis 6
dis 7
dis 8
dis 9
c                        // and continue
end
b 315                    // sets bp 10
commands 10              // re-enable after sigfillset
ena 2
ena 3
ena 4
ena 5
ena 6
ena 7
ena 8
ena 9
c                        // run body of aio_thread
end
c                        // run into aio_thread

Paolo