Re: valgrind support for glibc/kernel arm64 HWCAPS

[Siddhesh Poyarekar <siddhesh at gotplt dot org>]

On Thursday 06 July 2017 12:34 AM, Florian Weimer wrote:
> Why do you expect valgrind to be able to execute code specific to vendor
> CPUs?  That's not even true for i386 and x86-64 and micro-architecture
> ISA extensions.

The expectation is that it looks for potential memory access issues in
these low level functions themselves, but that is probably too much to
expect.  However this:

   (c) the glibc SSE-variants can read past the end of the input data
       ranges. This can cause false-positive Memcheck / Helgrind / DRD
       reports.

sounds scary.  It's been a while since I've looked at the x86 versions
of the string functions, do you (or Mark) know what this is referring to
and why it is safe?

It would be nice to get some more details of this one as well:

   (b) some of the normal versions are hyper-optimised, which fools
       Memcheck and cause spurious value warnings.  Our versions are
       simpler.

specifically whether it is x86-specific or true for other architectures
as well and what happens there.  If nothing, at least document it
somewhere so that noobs like me don't get alarmed when they see it :)

Siddhesh