Re: [PATCH 2/2][MIPS][RFC] Emit .note.GNU-stack for hard-float linux targets.

[Jeff Law <law@redhat.com>]

On Thu, 2020-01-23 at 10:58 +0000, Dragan Mladjenovic wrote:
> On 07.12.2019. 19:33, Jeff Law wrote:
> > On Thu, 2019-11-07 at 17:05 +0000, Dragan Mladjenovic wrote:
> > > On 01.11.2019. 11:32, Dragan Mladjenovic wrote:
> > > > On 10.08.2019. 00:15, Joseph Myers wrote:
> > > > > On Fri, 9 Aug 2019, Jeff Law wrote:
> > > > > 
> > > > > > > 2019-08-05  Dragan Mladjenovic  <dmladjenovic@wavecomp.com>
> > > > > > > 
> > > > > > >      * config.in: Regenerated.
> > > > > > >      * config/mips/linux.h (NEED_INDICATE_EXEC_STACK): Define
> > > > > > > to 1
> > > > > > >      for TARGET_LIBC_GNUSTACK.
> > > > > > >      * configure: Regenerated.
> > > > > > >      * configure.ac: Define TARGET_LIBC_GNUSTACK if glibc
> > > > > > > version is
> > > > > > >      found 2.31 or greater.
> > > > > > My only concern here is the configure bits.  So for example,
> > > > > > will it do
> > > > > > the right thing if you're cross-compiling to a MIPS linux
> > > > > > target?  If
> > > > > > so, how?  If not, do we need to make it a first class configure
> > > > > > option
> > > > > > so that it can be specified when building cross MIPS linux
> > > > > > toolchains?
> > > > > 
> > > > > The key point of using GCC_GLIBC_VERSION_GTE_IFELSE is that (a)
> > > > > it checks
> > > > > the target glibc headers if available when GCC is built and (b)
> > > > > if not
> > > > > available, you can still use --with-glibc-version when
> > > > > configuring
> > > > > GCC, to
> > > > > get the right configuration in a bootstrap compiler built before
> > > > > glibc is
> > > > > built (the latter is necessary on some architectures to get the
> > > > > right
> > > > > stack-protector configuration for bootstrapping glibc, but may be
> > > > > useful
> > > > > in other cases as well).
> > > > > 
> > > > > My main concern about this patch is the one I gave in
> > > > > <https://sourceware.org/ml/libc-alpha/2019-08/msg00086.html>
> > > > > about what
> > > > > the configuration mechanism should be, on a whole-toolchain
> > > > > level, to say
> > > > > whether you are OK with a requirement for a 4.8 or later kernel.
> > > > > 
> > > > 
> > > > Sorry for the late reply.
> > > > 
> > > > I was waiting to backport [1] to most of the glibc release branches
> > > > in
> > > > use, but I got sidetracked along the way.
> > > > 
> > > > After this patch lands the preferred way to configure gcc would be
> > > > using
> > > > --with-glibc-version=2.31 and to use said glibc.
> > > > If the user/distribution can live with minimal kernel requirement
> > > > of 4.8
> > > > the glibc used should be configured with --enable-kernel=4.8.
> > > > I also plan to backport the [1] to limit the opportunity for
> > > > building
> > > > the possibly broken glibc with the gcc w/ enabled .note.GNU-stack.
> > > > 
> > > > This is all tedious and user has to be aware of all of it to make
> > > > it
> > > > work, but hopefully over time the distributions will default to
> > > > --with-glibc-version=2.31 and --enable-kernel=4.8. I guess
> > > > providing the
> > > > detailed NEWS entry for this change would help a bit.
> > > > 
> > > > Is there any objections to getting this on the trunk before the end
> > > > of
> > > > stage1?
> > > > 
> > > > [1] https://sourceware.org/ml/libc-alpha/2019-08/msg00639.html
> > > > 
> > > 
> > > Small update and gentle ping. The glibc change was backported all
> > > the
> > > way back to 2.24.
> > I think this is fine.  And yes, we'd like to get it mentioned in the
> > release notes since I suspect folks will want the GNU-stack ELF notes.
> > 
> > jeff
> > 
> > 
> 
> I left this to fall through the cracks once again. In light of [1], is 
> there any leeway for me to push this now?
> 
> [1] https://gcc.gnu.org/ml/gcc/2020-01/msg00199.html
We generally allow more leeway for the ports simply because getting
something wrong doesn't have as wide an impact.  Additionally, you're
using a configure-time flag to turn on the new behavior which further
limits the impact if something were to go wrong.

So if you want to commit it now, go ahead

jeff
> 
>