RFR (S) 8217879: hs_err should print more instructions in hex dump

[Aleksey Shipilev]

On 1/29/19 11:57 AM, Thomas Stüfe wrote:
> On Tue, Jan 29, 2019 at 11:31 AM Aleksey Shipilev <shade at redhat.com <mailto:shade at redhat.com>> wrote:
> I would bail out right away for bogus/unreadable pc since those may happen more often than not.

I like the current code, because it exercises the "adjustment" part often, implicitly verifying it.

> Is this exponential stepping really necessary? You run a risk of loosing information, e.g. for a pc
> 250 bytes int a readable page preceeded with an unmapped one. This coding runs during error
> reporting, so no big speed concerns I think.

Yes, that would print "only" -128 bytes from that page; still much better than nothing.

I did exponential stepping because delivering hundreds of signals via SafeFetch is probably not a
good practice for both performance and debugging. I'd hate to "gdb cont" a hundred times :)

The ideal way out would be to have os::print_hex_dump that is page-aware and that can probe once per
page. But there is a bigger fish to fry, and this seems good for the overwhelming majority of cases,
and universally safe.

-Aleksey