Re: [Qemu-devel] [PATCH 0/7] Improve buffer_is_zero

[Adam Richter]

> * Richard Henderson (address@hidden) wrote:
>> Patches 1-3 remove the use of ifunc from the implementation.
[...]

I am not a qemu developer, but I wanted to write in support of
removing the use of ifunc.

I filed a glibc bug at
https://sourceware.org/bugzilla/show_bug.cgi?id=20480 that I actually
found from these ifuncs in qemu that results in an attempt to execute
and unexecutable page, under unusual conditions that were arguably my
fault but that could happen on other systems.  I have only attempted
to implement a partial fix for this, and I think a complete fix would
be difficult, and the scenario that remains unfixed involves a
security policy that would probably be popular for systems hosting
virtual machine (prohibiting mapping pages simultaneiously writable
and executable).

I hope that that consideration, combined with the micro-costs to
readability and portability of using and ELF specific and perhaps
currently GCC specific feature might tip the balance against the
savings of a level of function call indirection that I assume the use
of ifunc was intended to provide.

Adam