From 0f993845d723c87656552837b412994d6086f086 Mon Sep 17 00:00:00 2001 From: Andrii Nakryiko Date: Thu, 13 Aug 2020 13:49:44 -0700 Subject: [PATCH] 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: Andrii Nakryiko Signed-off-by: Alexei Starovoitov Link: https://lore.kernel.org/bpf/20200813204945.1020225-9-andriin@fb.com --- tools/bpf/bpftool/gen.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c index db80e836816e..f61184653633 100644 --- a/tools/bpf/bpftool/gen.c +++ b/tools/bpf/bpftool/gen.c @@ -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) {