Commit 0f993845 authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
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tools/bpftool: Generate data section struct with conservative alignment 



The comment in the code describes this in good details. Generate such a memory
layout that would work both on 32-bit and 64-bit architectures for user-space.

Signed-off-by: default avatarAndrii Nakryiko <andriin@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200813204945.1020225-9-andriin@fb.com
parent 5705d705

tools/bpf/bpftool/gen.c

+14 −0
Original line number Diff line number Diff line
@@ -143,6 +143,20 @@ static int codegen_datasec_def(struct bpf_object *obj, 
			      var_name, align);

			return -EINVAL;

		}

		/* Assume 32-bit architectures when generating data section

		 * struct memory layout. Given bpftool can't know which target

		 * host architecture it's emitting skeleton for, we need to be

		 * conservative and assume 32-bit one to ensure enough padding

		 * bytes are generated for pointer and long types. This will

		 * still work correctly for 64-bit architectures, because in

		 * the worst case we'll generate unnecessary padding field,

		 * which on 64-bit architectures is not strictly necessary and

		 * would be handled by natural 8-byte alignment. But it still

		 * will be a correct memory layout, based on recorded offsets

		 * in BTF.

		 */

		if (align > 4)

			align = 4;



		align_off = (off + align - 1) / align * align;

		if (align_off != need_off) {