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

[Laszlo Ersek]

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).

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,
Laszlo

>
> Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
> ---
> Patch to review with --ignore-all-space
> ---
>  roms/edk2-funcs.sh | 48 +++++++++++++++++++---------------------------
>  1 file changed, 20 insertions(+), 28 deletions(-)
>
> diff --git a/roms/edk2-funcs.sh b/roms/edk2-funcs.sh
> index 3f4485b201..a455611c0d 100644
> --- a/roms/edk2-funcs.sh
> +++ b/roms/edk2-funcs.sh
> @@ -135,35 +135,27 @@ qemu_edk2_get_toolchain()
>      return 1
>    fi
>
> -  case "$emulation_target" in
> -    (arm|aarch64)
> -      printf 'GCC5\n'
> +  if ! cross_prefix=$(qemu_edk2_get_cross_prefix "$emulation_target"); then
> +    return 1
> +  fi
> +
> +  gcc_version=$("${cross_prefix}gcc" -v 2>&1 | tail -1 | awk '{print $3}')
> +  # Run "git-blame" on "OvmfPkg/build.sh" in edk2 for more information on
> +  # the mapping below.
> +  case "$gcc_version" in
> +    ([1-3].*|4.[0-7].*)
> +      printf '%s: unsupported gcc version "%s"\n' \
> +        "$program_name" "$gcc_version" >&2
> +      return 1
>        ;;
> -
> -    (i386|x86_64)
> -      if ! cross_prefix=$(qemu_edk2_get_cross_prefix "$emulation_target"); 
> then
> -        return 1
> -      fi
> -
> -      gcc_version=$("${cross_prefix}gcc" -v 2>&1 | tail -1 | awk '{print 
> $3}')
> -      # Run "git-blame" on "OvmfPkg/build.sh" in edk2 for more information on
> -      # the mapping below.
> -      case "$gcc_version" in
> -        ([1-3].*|4.[0-7].*)
> -          printf '%s: unsupported gcc version "%s"\n' \
> -            "$program_name" "$gcc_version" >&2
> -          return 1
> -          ;;
> -        (4.8.*)
> -          printf 'GCC48\n'
> -          ;;
> -        (4.9.*|6.[0-2].*)
> -          printf 'GCC49\n'
> -          ;;
> -        (*)
> -          printf 'GCC5\n'
> -          ;;
> -      esac
> +    (4.8.*)
> +      printf 'GCC48\n'
> +      ;;
> +    (4.9.*|6.[0-2].*)
> +      printf 'GCC49\n'
> +      ;;
> +    (*)
> +      printf 'GCC5\n'
>        ;;
>    esac
>  }
>