Quality Feedback Agent
From MozillaZine Knowledge Base
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Revision as of 22:46, 22 October 2005
Talkback (aka Quality Feedback Agent) is a program that activates when Mozilla Suite, Firefox, or Thunderbird crashes. It lets you send stack traces and other development information to mozilla.org engineers. This information helps developers make future versions of the software crash less.
Talkback is usually bundled with Firefox/Thunderbird/Mozilla Suite. However to install it you may need to do a "Custom" installation and select "Quality Feedback Agent" component manually.
Q: How can I tell whether Talkback is installed?
Q: How can I get Talkback if it isn't already installed?
Q: I have Talkback installed, but it doesn't appear to work!
How does mozilla.org use Talkback data?
Talkback data is used in two ways:
What is a stack trace?
A stack trace is a function call stack, often helpful for understanding the cause of a bug. For a crash, it shows the function in which the crash occurred, what function called that function, etc.
Once I submit a Talkback report, how can I get a stack trace?
Each report the Agent sends has its own Talkback ID, which you can see in Talkback's window. The ID looks like "TB4895329Q" and this is what you need to post to bugzilla when you're asked to post a talkback ID.
However if you're curious, you can see the stack trace of your crash by entering your Talkback ID into Talkback FastFind.
Can I submit Talkback reports for hangs?
While Talkback theoretically supports hang reports, I don't know how make it trigger for them.
timeless has written a program called crash.exe that can be used to force Firefox to crash, but it makes Firefox crash in a new thread, so it doesn't create a useful stack trace for hangs. A future version of crash.exe might let you specify a thread to crash, which could be used in combination with Sysinternals Process Explorer to make the hanging thread crash.
Talkback and Bugzilla
If I submit a crash report, should I still file a bug report in Bugzilla?
Yes. Unless you file a bug, your crash report will only be used in statistics to find topcrashers.
How can I submit a useful bug report for a crash?
Once you reproduced the crash, send the Talkback report, then copy the ID from the Talkback window. (On some platforms, you must run talkback.exe before you'll see the Talkback window.) Go to Talkback FastFind and enter your ID. If everything works correctly, you'll get a page with report details.
Try to find existing bug reports about your crash. Search based on the signature (listed separately in the Talkback report, usually the name of the top function in the stack trace). For example, if the signature is
When submitting your bug, you can include the Talkback ID in your bug report instead of the full stack trace. In your summary for the bug, include the name of the function. For example, "Crash [@ CSSStyleRuleImpl::DeclarationChanged] toggling visibility value via DOM Inspector".
It's also important to pick the right component for your crash.
If you can figure out easy steps to reproduce and create a small testcase, do so!
Should I file the crash as a security-sensitive bug?
Usually not. If the crash is just a denial of service (DoS), Mozilla's security group probably isn't interested.
If the crash is in NSS or NSPR, it should be considered a security hole. These components are also used by some server software, so crashes in these components are considered security holes even if the most an attacker could do is cause a DoS.
If the top of the stack is a random memory address instead of a function name, that means Mozilla crashed when trying to jump to an incorrect address. If the attacker can control the address Mozilla jumps to, he can probably cause Mozilla to execute arbitrary machine code instead of crashing. Even if the address appears to be random, the attacker might be able to put enough copies of his code throughout memory with nop slides to exploit the crash. In addition to looking at the stack, you can inspect the C++ code by clicking the links in the Talkback report.
If you file the bug as security-sensitive, say why you did, e.g. "I'm filing this crash bug as security-sensitive because it is in NSS and NSS maintainers consider DoSes to be security holes".