BTF flattens n-dym arrays

[ttreyer]

BTF flattens multi-dimensional arrays into 1-D array.

The tests field_analyser_btf.btf_types and clang_parser_btf.btf had to be modified as follow:

• We can't test each dimension of the array properly
• The number of element for Foo1.d was set to 12 instead of the correct number 3

What reproduces the bug? Provide code if possible.

Modify field_analyser_btf.btf_types and clang_parser_btf.btf so they use the commented code for the field Foo1.d.

[ajor]

I think this is a problem with pahole's DWARF -> BTF translator: https://git.kernel.org/pub/scm/devel/pahole/pahole.git/tree/btf_encoder.c#n1199

We use it to generate our test BTF data here:

bpftrace/tests/data/CMakeLists.txt

Lines 16 to 22 in 3691e71

	add_custom_command(
	OUTPUT ${DATA_SOURCE_O}
	COMMAND gcc -g -o ${DATA_SOURCE_O} ${DATA_SOURCE_C}
	# pahole uses LLVM_OBJCOPY env var.
	# We must hack it like this b/c cmake does not support setting env vars at build time
	COMMAND bash -c "LLVM_OBJCOPY=${LLVM_OBJCOPY} pahole -J ${DATA_SOURCE_O}"
	DEPENDS ${DATA_SOURCE_C})