Re: [PATCH-for-5.0] roms/edk2-funcs.sh: Use available GCC for ARM/Aarch64 targets

[Ard Biesheuvel]

On Thu, 5 Dec 2019 at 16:27, Philippe Mathieu-Daudé <address@hidden> wrote:
>
> On 12/5/19 5:13 PM, Laszlo Ersek wrote:
> > Hi Phil,
> >
> > (+Ard)
> >
> > On 12/04/19 23:12, Philippe Mathieu-Daudé wrote:
> >> Centos 7.7 only provides cross GCC 4.8.5, but the script forces
> >> us to use GCC5. Since the same machinery is valid to check the
> >> GCC version, remove the $emulation_target check.
> >>
> >>    $ cat /etc/redhat-release
> >>    CentOS Linux release 7.7.1908 (Core)
> >>
> >>    $ aarch64-linux-gnu-gcc -v 2>&1 | tail -1
> >>    gcc version 4.8.5 20150623 (Red Hat 4.8.5-16) (GCC)
> >
> > this patch is not correct, in my opinion. ARM / AARCH64 support in edk2
> > requires GCC5 as a minimum. It was never tested with an earlier
> > toolchain, to my understanding. Not on my part, anyway.
> >
> > To be more precise: when I tested cross-gcc toolchains earlier than
> > that, the ArmVirtQemu builds always failed. Minimally, those toolchains
> > didn't recognize some of the AARCH64 system registers.
> >
> > If CentOS 7.7 does not provide a suitable (>=GCC5) toolchain, then we
> > can't build ArmVirtQemu binaries on CentOS 7.7, in my opinion.
> >
> > Personally, on my RHEL7 laptop, over time I've used the following
> > toolchains, to satisfy the GCC5 requirement of ArmVirtQemu (which
> > requirement I took as experimental evidence):
> >
> > - Initially (last quarter of 2014), I used binary distributions --
> >    tarballs -- of cross-binutils and cross-gcc, from Linaro.
> >
> > - Later (last quarter of 2016), I rebuilt some SRPMs that were at the
> >    time Fedora-only for RHEL7. Namely:
> >
> >    - cross-binutils-2.27-3.fc24
> >      https://koji.fedoraproject.org/koji/buildinfo?buildID=801348
> >
> >    - gcc-6.1.1-2.fc24
> >      https://koji.fedoraproject.org/koji/buildinfo?buildID=761767
> >
> > - Most recently, I've been using cross-binutils updated from EPEL7:
> >
> >    - cross-binutils-2.27-9.el7.1
> >      https://koji.fedoraproject.org/koji/buildinfo?buildID=918474
> >
> > To my knowledge, there is still no suitable cross-compiler available on
> > RHEL7, from any trustworthy RPM repository. So, to this day, I use
> > gcc-6.1.1-2 for cross-building ArmVirtQemu, on my RHEL7 laptop.
> >
> > Again: I believe it does not matter if the gcc-4.8.5-based
> > cross-compiler in CentOS 7 "happens" to work. That's a compiler that I
> > have never tested with, or vetted for, upstream ArmVirtQemu.
> >
> > Now, I realize that in edk2, we have stuff like
> >
> >    GCC48_AARCH64_CC_FLAGS
> >
> > in "BaseTools/Conf/tools_def.template" -- coming from commit
> > 7a9dbf2c94d1 ("BaseTools/Conf/tools_def.template: drop ARM/AARCH support
> > from GCC46/GCC47", 2019-01-08). That doesn't change the fact that I've
> > never built or tested ArmVirtQemu with such a compiler. And so this
> > patch makes me quite uncomfortable.
> >
> > If that rules out CentOS 7 as a QEMU project build / CI platform for the
> > bundled ArmVirtQemu binaries, then we need a more recent platform
> > (perhaps CentOS 8, not sure).
>
> Unfortunately CentOS 8 is not available as a Docker image, which is a
> convenient way to build EDK2 in a CI.
>
> > I think it's also educational to check the origin of the code that your
> > patch proposes to remove. Most recently it was moved around from a
> > different place, in QEMU commit 65a109ab4b1a ('roms: lift
> > "edk2-funcs.sh" from "tests/uefi-test-tools/build.sh"', 2019-04-17).
> >
> > In that commit, for some reason I didn't keep the original code comments
> > (perhaps it would have been too difficult or messy to preserve the
> > comments sanely with the restructured / factored-out code). But, they
> > went like this (originally from commit 77db55fc8155,
> > "tests/uefi-test-tools: add build scripts", 2019-02-21):
> >
> > # Expose cross_prefix (which is possibly empty) to the edk2 tools. While at 
> > it,
> > # determine the suitable edk2 toolchain as well.
> > # - For ARM and AARCH64, edk2 only offers the GCC5 toolchain tag, which 
> > covers
> > #   the gcc-5+ releases.
> > # - For IA32 and X64, edk2 offers the GCC44 through GCC49 toolchain tags, in
> > #   addition to GCC5. Unfortunately, the mapping between the toolchain tags 
> > and
> > #   the actual gcc releases isn't entirely trivial. Run "git-blame" on
> > #   "OvmfPkg/build.sh" in edk2 for more information.
> > # And, because the above is too simple, we have to assign cross_prefix to an
> > # edk2 build variable that is specific to both the toolchain tag and the 
> > target
> > # architecture.
> >
> > So... unless Ard feels it is really totally safe to retro-actively rely
> > on the gcc-4.8.5-based compiler in CentOS 7, I'd rather we picked a more
> > recent build platform (OS) instead. For example, we build ArmVirtQemu on
> > RHEL8 regularly, so that's a reality-based "plus" for CentOS 8.
> >
> >
> > Independently of all of the above, the OVMF toolchain selection logic
> > that this patch proposes to reuse with ArmVirtQemu, is *really*
> > x86-specific. Please run "git blame" on "OvmfPkg/build.sh" in upstream
> > edk2, to see where the various branches come from (as the comments in
> > this shell script suggest as well). There had been mess like commit
> > 656ac0c7d8ea ('Revert "OvmfPkg/build.sh: select the GCC49 toolchain
> > settings for gcc-7.*"', 2017-08-25).
>
> Thanks for all the pointers, very educative indeed :)
>
> I'll see other setups I can use with GCC5+ available.
>
> I still have to figure if there are free tier CI with less limitations
> than Travis/Shippable/GitLab, so we can keep the full EDK2 build output log.
>

My CI job for ArmVirtQemu/EDK2 build tested GCC48 and GCC49 until very
recently, and I never experienced any issues when running those
images, although it's been much longer that I actually tried that. So
I wouldn't recommend against it, and if we do identify any issues, we
should either deprecate GCC48 (for ArmVirtQemu or for AArch64
altogether) or fix them.