build: Use -fcf-protection for GCC >= 8 or Clang >= 7

[Krechals]

Prerequisite checklist

• Read the contribution guidelines regarding submitting new changes to the project;
• Tested your changes against relevant architectures and platforms;
• Ran the checkpatch.uk on your commit series before opening this PR;
• Updated relevant documentation.

Base target

• Architecture(s): [e.g. x86_64 or N/A]
• Platform(s): [e.g. kvm, xen or N/A]
• Application(s): [e.g. app-python3 or N/A]

Additional configuration

Description of changes

The build fails on every app when gcc-8.0+ isn't used.

-fcf-protection was introduced in gcc-8.0 and in clang-7.0.

The build still fails for clang-7.0, since __asm__ goto from plat/kvm/x86/traps.c was introduced in clang-9.0.

GitHub-Depends-On: #983

[StefanJum]

This looks fine @Krechals, thank you, see the one comment.

About the build still failing with clang 7, should we add a global check for the clang version and fail if it's <= 9 (it could be only for x86_64 or whatever setup fails to build)?
Something like this.

--- LATER EDIT: This will be done by #949

I would also split the PR into 2 commits, one that adds the -fcf-protection flag and one that adds the error_if_clang_version_lt rule to the build system.

[razvand]

@Krechals, could you please take a look in this PR to have it ready for upstream? See @StefanJum's comments. @mariasfiraiala , please also take a look.

[mariasfiraiala]

This works fine, thanks! @Krechals can you please address @StefanJum's comments in order to have this merged? I think they make sense.

[razvand]

@Krechals , could you please rebase this PR on top of #983 ? Simply add the -fcf-protection specific checks commit and use the Clang-specific Makefile updates from #983 .

[razvand]

@Krechals , could you rebase this, now that PR #983 is in?

[mariasfiraiala]

All good, thanks!

Reviewed-by: Maria Sfiraiala maria.sfiraiala@gmail.com

[StefanJum]

This commit adds a minimum compiler version check, which is 9.0 for clang. So we only need the check for gcc.

Something like

ifeq ($(call have_gcc),y)
COMPFLAGS-$(call gcc_version_ge,8,0)	+= -fcf-protection=none
else
COMPFLAGS-y += -fcf-protection=none
endif

or

COMPFLAGS-$(call gcc_version_ge,8,0)	+= -fcf-protection=none
COMPFLAGS-$(call have_clang) += -fcf-protection=none

could be better?

[StefanJum]

All good now @Krechals, just please remove the id (101668) from the commit authored-by and sign-off tags, we can merge after that.

[unikraft-bot]

✅ Checkpatch passed

Beep boop! I ran Unikraft's checkpatch.pl support script on your pull request and it all looks good!

SHA	commit	checkpatch
2906df3	build: Use -fcf-protection for GCC >= 8 or Clang >= 7	✅

[StefanJum]

All good, thanks.

Reviewed-by: Stefan Jumarea stefanjumarea02@gmail.com

[razvand]

Approved-by: Razvan Deaconescu razvand@unikraft.io