[webkit-dev] Always-on diagnostic code Re: [webkit-changes] [96819] trunk/Source/WebCore

[Dan Bernstein]

On Oct 6, 2011, at 9:40 AM, gavinp at chromium.org wrote:

> Modified: trunk/Source/WebCore/dom/ScriptElement.h (96818 => 96819)
> 
> --- trunk/Source/WebCore/dom/ScriptElement.h	2011-10-06 16:37:35 UTC (rev 96818)
> +++ trunk/Source/WebCore/dom/ScriptElement.h	2011-10-06 16:40:47 UTC (rev 96819)
> @@ -113,6 +113,14 @@
>        ZeroedInStopLoadRequest,
>        ZeroedInNotifyFinished,
>      } m_cachedScriptState;
> +
> +    // We grab a backtrace when we zero m_cachedScript, so that at later crashes
> +    // we'll have a debuggable stack.
> +    enum {
> +        MaxBacktraceSize = 32
> +    };
> +    int m_backtraceSize;
> +    void* m_backtrace[MaxBacktraceSize];
>  };

This appears to increase the size of each ScriptElement instance by 256 bytes. I don’t know how bad a performance hit this is in real-world use, but it is most certainly not something all vendors would like to include in their releases. The way this change was made, however, it is almost inevitable that a vendor would end up unknowingly shipping this performance regression. This change was made on trunk, it is unconditionally compiled in, and there is nothing obvious tracking undoing this change.

I think this is the wrong way to incorporate diagnostic code into WebKit.
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