From: Andrii Nakryiko <andriin@fb.com>
To: <bpf@vger.kernel.org>, <netdev@vger.kernel.org>, <ast@fb.com>,
<daniel@iogearbox.net>
Cc: <andrii.nakryiko@gmail.com>, <kernel-team@fb.com>,
Andrii Nakryiko <andriin@fb.com>
Subject: [PATCH v3 bpf 8/9] tools/bpftool: generate data section struct with conservative alignment
Date: Thu, 13 Aug 2020 13:49:44 -0700 [thread overview]
Message-ID: <20200813204945.1020225-9-andriin@fb.com> (raw)
In-Reply-To: <20200813204945.1020225-1-andriin@fb.com>
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>
---
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) {
--
2.24.1
next prev parent reply other threads:[~2020-08-13 20:50 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-13 20:49 [PATCH v3 bpf 0/9] Fix various issues with 32-bit libbpf Andrii Nakryiko
2020-08-13 20:49 ` [PATCH v3 bpf 1/9] tools/bpftool: fix compilation warnings in 32-bit mode Andrii Nakryiko
2020-08-13 20:49 ` [PATCH v3 bpf 2/9] selftest/bpf: " Andrii Nakryiko
2020-08-13 20:49 ` [PATCH v3 bpf 3/9] libbpf: fix BTF-defined map-in-map initialization on 32-bit host arches Andrii Nakryiko
2020-08-13 20:49 ` [PATCH v3 bpf 4/9] libbpf: handle BTF pointer sizes more carefully Andrii Nakryiko
2020-08-13 20:49 ` [PATCH v3 bpf 5/9] selftests/bpf: fix btf_dump test cases on 32-bit arches Andrii Nakryiko
2020-08-13 20:49 ` [PATCH v3 bpf 6/9] libbpf: enforce 64-bitness of BTF for BPF object files Andrii Nakryiko
2020-08-13 20:49 ` [PATCH v3 bpf 7/9] selftests/bpf: correct various core_reloc 64-bit assumptions Andrii Nakryiko
2020-08-13 20:49 ` Andrii Nakryiko [this message]
2020-08-13 20:49 ` [PATCH v3 bpf 9/9] selftests/bpf: make test_varlen work with 32-bit user-space arch Andrii Nakryiko
2020-08-14 0:08 ` [PATCH v3 bpf 0/9] Fix various issues with 32-bit libbpf Alexei Starovoitov
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