cilium: "'stddef.h' file not found" in dev. VM

Issue

Trying to run the unit tests from inside the dev. VM results in the following error:

In file included from unit-test.c:8:
/usr/include/stdlib.h:31:10: fatal error: 'stddef.h' file not found
#include <stddef.h>

That error is happening because we recently switched the compiler for the BPF unit tests to Clang. The dev. VM images (4.9 and net-next) don’t include a full Clang, but only the strict minimum required to compile BPF programs.

Workaround

The following steps, proposed by André for a similar issue on v1.7, work as a quick fix:

sudo mv /usr/bin/clang{,.bak}
sudo mv /usr/bin/llc{,.bak}
sudo apt-get install -y clang-7 llvm-7
sudo update-alternatives --install /usr/bin/clang clang /usr/lib/llvm-7/bin/clang 1000
sudo update-alternatives --install /usr/bin/llc llc /usr/lib/llvm-7/bin/llc 1000

To revert:

sudo mv /usr/bin/clang{.bak,}
sudo mv /usr/bin/llc{.bak,}

Proper Fix

The proper fix requires to revert part of cilium/packer-ci-build#200, to be able to compile on x86 with Clang.

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Reported-by: Nate Sweet nathanjsweet@pm.me