Since crash bugs are a top priority within Adobe, there is one relatively simple step Adobe should take which would make it much easier for everyone else to help Adobe track and diagnose crashes: implement a symbol server.

A symbol server is a public web server from which developers can fetch debugging information (PDB files) for released binaries. The Microsoft debuggers have excellent support for automatically pulling down symbols as they are needed in the debugger. Mozilla runs a symbol server for Firefox nightlies and releases, which is invaluable for people debugging and profiling Firefox without having to do a custom build. Microsoft runs a symbol server which contains debug information for Windows and many other Microsoft products, including the Silverlight plugin.

Debug information is not simply a way to get symbolic information from Flash. It is necessary in order to get any useful stack trace of the Mozilla code which is calling Flash. A common compiler optimization called frame pointer omission (FPO) avoids storing the frame pointer in the x86 EBP register, freeing that register up for general use. In order to walk the stack of this optimized code, the debugger has to query the frame size and frame pointer information from the PDB file. When debug information is not available, stack walking doesn’t produce usable results.

As an example, take the current #3 topcrash for nightly builds of Firefox (mozilla-central). The signature for this crash is NPSWF32.dll@0x1e7fe4. The stack traces from Mozilla’s crash reporting system are completely opaque:

Even worse, the crash signature depends on the particular version of Flash that is installed on the user’s computer. We can’t tell if a particular crash signature is fixed by a new revision of flash because without symbols we can’t correlate crashes between different versions.

As part of developing multi-process plugins for Firefox, we are constantly dealing with unexpected plugin behaviors. Whenever we encounter a problem which can be reproduced in both Silverlight and Flash, we’ll always test with silverlight, simply because Microsoft makes Silverlight symbols available through their symbol server and therefore we can actually step through their code and ours in a debugger.

Adobe should set up a symbol server for their three main plugins, Flash, Shockwave, and Acrobat. By implementing this simple tool, Adobe could help all browser vendors and interested hackers to help identify and fix bugs. If Adobe is concerned about using full debug information to reverse-engineer details of their code, there is a way to strip the PDB files so that only frame-pointer information and function names.

Not infrequently, there are bugs filed in Mozilla by Smart People who want to help and who are experiencing an odd behavior or a bug. They want to help, but they really don’t want to spend the time to build Mozilla themself (and I really don’t blame them).

Now, at least on Windows, interested hackers have the ability to debug release builds of Firefox! Mozilla finally has its own symbol server which will provide debugging PDBs for nightly and release builds. See the Mozilla Developer Center for more information about using this new and exciting service. Note that this will only work for trunk builds from 1.9a5 forward, so it won’t be much help with our current Firefox 2.0.0.x release series. If you want to disable breakpad crash reporting and have crashes in nightly builds go straight to the Windows JIT debugging system, export MOZ_CRASHREPORTER_DISABLE=1 in your environment.

Kudos to Ted and Aravind for getting this set up.