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tools/bpftool: Generate data section struct with conservative alignment

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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 <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200813204945.1020225-9-andriin@fb.com
This commit is contained in:
Andrii Nakryiko 2020-08-13 13:49:44 -07:00 committed by Alexei Starovoitov
parent 5705d70583
commit 0f993845d7
1 changed files with 14 additions and 0 deletions
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14
tools/bpf/bpftool/gen.c
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@ -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) {