fix(driver/ebpf): fixed eBPF issues on clang5

[FedeDP]

Signed-off-by: Federico Di Pierro nierro92@gmail.com

What type of PR is this?

/kind bug

Any specific area of the project related to this PR?

/area driver-ebpf

What this PR does / why we need it:

It fixes some incompatibilities between eBPF probe and clang5.
Clang5 is provided with falco-builder docker image, thus it is important to support it; see see falcosecurity/falco#1761.
Tested on kernel 4.19.0 and clang 5.0.1, and kernel 5.14.14 and clang 12.0.1.
As the PR actually just adds some checks, i think we can skip the full test matrix.

All the following changes are mandatory:

• bound check state->n_drops_X counters
• moved off_bounded declaration near its usage in bpf_parse_readv_writev_bufs()
• force-disable switch jump table

The latter one was the most tricky: it seems like we already disable jump table in our makefile with the -fno-jump-tables flag.
But it seems like clang-5 with -O2 optimization flags, still somewhat makes use of them.
Thus, use a "smart" trick to disable them in any case.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

fix(driver/ebpf): fix ebpf probe on clang5.

[poiana]

Hi @FedeDP. Thanks for your PR.

I'm waiting for a falcosecurity member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[FedeDP]

It seems like we still got some issues on falco-builder env: falcosecurity/falco#1761 (comment)

Let's keep this open in wip mode to track all the required fixes.

[FedeDP]

It was an user mistake, the patch is working fine!

[leogr]

/ok-to-test

[FedeDP]

More tests:

• clang 14.0.0 on linux 4.19.0
• clang 12.0.1 on linux 4.19.0
• clang 7.0.1 on linux 4.19.0
• clang 10.0.0 on linux 5.11.0
  I think this is safe to go.

[poiana]

LGTM label has been added.

Git tree hash: 17c470fe23f300758c47c86d8cbd7cdcb8919a2c

[leogr]

/approve

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: FedeDP, leogr

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