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Upcoming “experimental feature” will help you detect use of uninitialized memory

By Roger Andrews, Posted on December 10, 2008 at 7:05 pm

We are continually reviewing customer applications to assist with support/development issues, and in doing so often come up with ideas to help customers facilitate debugging problems they may encounter. We use a product from Compuware called DevPartner Studio to help us track down “C” variable access problems in the Synergy components that sometimes cause instability in the runtime. I like to run customer applications with a special runtime that is built with DevPartner, which allows us to check boundary conditions while running “real” customer applications. DevPartner enables us to check use of memory already freed (called dangling pointers) and access to memory before we have written to it (a common cause of symptoms that move around depending on memory and time of day).

One recent application we saw was accessing uninitialized memory before writing to it. As we tracked this down, , we realized the customer was using stack records and %MEMPROC memory that had never been written to. In certain cases this would cause random results, and in this particular case, it was causing the customer’s application to fail when run under the DevPartner tool because the memory was now a consistent but unexpected value.

We decided as a test to add some support in Synergy/DE to see if the Synergy runtime could also detect this use of uninitialized memory with a minimal overhead when running in debug. It turns out that we can do similar checking for assignment statements and “if” tests, and we can differentiate between stack memory and MEM_PROC memory. Using this functionality also enables a developer to break in the debugger after the statement that uses this random memory.

We are considering adding this new debugging functionality to a future release of Synergy/DE. However, so that we can get this useful tool into your hands sooner, we are planning to include it as an “experimental feature” in an upcoming patch.

“Experimental features” are features that are under evaluation. They are for early adopters to use and provide us with feedback on. They will be supported, but they may be modified or even removed in subsequent releases.

So look for this new experimental debugging feature in an upcoming patch and consider trying it out. Like the recent feature we added to detect mismatched global data-section sizes (which can cause runtime crashes), this feature to detect uninitialized memory continues our aim to add debug-time detection of coding errors to assist you in producing more reliable applications.

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