RFR: 8342607: Enhance register printing on x86_64 platforms

[Thomas Stuefe]

On Tue, 22 Oct 2024 19:42:47 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

> > Well, with my quick-search I found information like that too. I don't see though, how it helps understand that the printed values are correct.
> 
> I think the only way to verify that the printed values are correct is testing it. I'm currently experimenting with setting up XMM values and then crashing intentionally. I can see that my values get printed, but on linux, XMM[0] seems to be always 0 and the other registers off by one. Strange.

I got curious, then confused, and looked. See https://stackoverflow.com/questions/43415882/reading-sse-registers-xmm-ymm-in-a-signal-handler - even though it refers to ymm registers. The answer seems to indicate that the glibc structure is not what you should be using, but going via uc_mcontext seems to be the right way.

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PR Comment: https://git.openjdk.org/jdk/pull/21615#issuecomment-2431201868