[aarch64-port-dev ] [Roland Westrelin] Re: Aarch64 port for ZGC, so far

[Andrew Dinn]

On 15/04/2019 09:56, Stuart Monteith wrote:
> Hello,
>   I'm afraid this is the expected behaviour:
>     https://www.kernel.org/doc/Documentation/arm64/tagged-pointers.txt
> 
> So it is explicit in stating that we don't pass tagged addresses to the kernel.
"Non-zero tags are not preserved when delivering signals. This means
that signal handlers in applications making use of tags cannot rely on
the tag information for user virtual addresses being maintained for
fields inside siginfo_t. One exception to this rule is for signals
raised in response to watchpoint debug exceptions, where the tag
information will be preserved."

Yikes! Does that not imply that when we return from a SIGSEGV into a
handler that an oop held in a register may have its tags wiped?

regards,


Andrew Dinn
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