RFR: 8247514: Improve clhsdb 'findpc' ability to determine what an address points to by improving PointerFinder and PointerLocation classes

[Yasumasa Suenaga]

On Sun, 17 Jan 2021 03:57:59 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

> See the bug for most details. A few notes here about some implementation details:
> 
> In the `PointerLocation` class, I added more consistency w.r.t. whether or not a newline is printed. It used to for some address types, but not others. Now it always does. And if you see a comment something like the following:
> 
> `         getTLAB().printOn(tty); // includes "\n" `
> 
> That's just clarifying whether or not the `printOn()` method called will include the newline. Some do and some don't, and knowing what the various `printOn()` methods do makes getting the proper inclusion of the newline easier to understand.
> 
> I added `verbose` and `printAddress` boolean arguments to `PointerLocation.printOn()`. Currently they are always `true`. The false arguments will be used when I complete [JDK-8250801](https://bugs.openjdk.java.net/browse/JDK-8250801), which will use `PointerFinder/Location` to show what each register points to.
> 
> The CR mentions that the main motivation for this work is for eventual replacement of the old clhsdb `whatis` command, which was implemented in javascript. It used to resolve DSO symbols, whereas `findpc` did not. The `whatis` code did this with the following:
> 
>   var dso = loadObjectContainingPC(addr);
>   if (dso == null) {
>     return ptrLoc.toString();
>   }
>   var sym = dso.closestSymbolToPC(addr);
>   if (sym != null) {
>     return sym.name + '+' + sym.offset;
>   }
> And now you'll see something similar in the PointerFinder code:
> 
>         loc.loadObject = cdbg.loadObjectContainingPC(a);
>         if (loc.loadObject != null) {
>             loc.nativeSymbol = loc.loadObject.closestSymbolToPC(a);
>             return loc;
>         } 
> Note that now that `findpc` does everything that `whatis` used to (and more), we don't really need to add a java version of `whatis`, but I'll probably do so anyway just help out people who are used to using the `whatis` command. That will be done using [JDK-8244670](https://bugs.openjdk.java.net/browse/JDK-8244670)

LGTM

-------------

Marked as reviewed by ysuenaga (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/2111