This is the mail archive of the
libc-alpha@sourceware.org
mailing list for the glibc project.
Re: [PATCH 0/2] Multiarch hooks for memcpy variants
On Fri, Aug 11, 2017 at 1:58 PM, Szabolcs Nagy <szabolcs.nagy@arm.com> wrote:
>
> as far as i understand *_chk calls are only generated when
> compiling with -D_FORTIFY_SOURCE=* and most of these checks
> could be inlined by the compiler (i.e. there is no need
> for runtime support in principle).
Calls to _chk functions that survive in the executable are for cases
where the compiler couldn't prove the call was safe - for instance, if
the size of data copied can vary at runtime.
Using _FORTIFY_SOURCE means you accept *some* extra overhead, but we
don't want it to sacrifice *all* machine-specific optimizations.
People do things like compiling entire "hardened" distributions with
it on.
> may be the generic __memcpy_chk should call the ifunced
> memcpy so it goes through an extra plt indirection, but
> at least less target specific code is needed.
I was thinking of making this suggestion myself. I think that would
be a better maintainability/efficiency tradeoff. (Of course, I also
think we shouldn't bypass ifuncs for intra-libc calls.)
zw