RFR: 8250801: Add clhsdb "threadcontext" command

[Kevin Walls]

On Thu, 23 Dec 2021 04:06:58 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

> SA has the ability to fetch the thread's registers via the thread context. It would be nice to allow access to the registers from clhsdb. This plays in well with the enhancements being done to PointerFinder as part of JDK-8247514. Many of the register values will then be automatically displayed as symbols, Methods, Threads, stack offsets, nmethods, interpreter codelets, etc.
> 
> During some recent debugging I did I found it useful to dump a thread's registers in this manner. Although in this case I was inlining the code in the part of SA where I wanted to see the registers, having it as a clhsdb command would not only be useful to user, but also useful when debugging SA because it would serve as a code snippet to copy-n-paste where needed.
> 
> The syntax is:
> 
>     threadcontext [-v] { -a | id }
> 
> Where -a displays all threads, and "id" is used to display a specific thread. This is the same argument syntax as some other commands that let  you choose all threads or just one thread, such as the "thread" and "where" commands. -v just means more verbose output, whereas without it for the most part each register printed will just take up one line.

Looks useful to expose this info if we have it!

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Marked as reviewed by kevinw (Committer).

PR: https://git.openjdk.java.net/jdk/pull/6925