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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 bpf 8/9] tools/bpftool: generate data section struct with conservative alignment
Date: Thu, 13 Aug 2020 00:17:21 -0700	[thread overview]
Message-ID: <20200813071722.2213397-9-andriin@fb.com> (raw)
In-Reply-To: <20200813071722.2213397-1-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 8a4c2b3b0cd6..17507fba9eb2 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


  parent reply	other threads:[~2020-08-13  7:17 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-13  7:17 [PATCH bpf 0/9] Fix various issues with 32-bit libbpf Andrii Nakryiko
2020-08-13  7:17 ` [PATCH bpf 1/9] tools/bpftool: fix compilation warnings in 32-bit mode Andrii Nakryiko
2020-08-13  7:17 ` [PATCH bpf 2/9] selftest/bpf: " Andrii Nakryiko
2020-08-13  7:17 ` [PATCH bpf 3/9] libbpf: fix BTF-defined map-in-map initialization on 32-bit host arches Andrii Nakryiko
2020-08-13  7:17 ` [PATCH bpf 4/9] libbpf: handle BTF pointer sizes more carefully Andrii Nakryiko
2020-08-13  7:17 ` [PATCH bpf 5/9] selftests/bpf: fix btf_dump test cases on 32-bit arches Andrii Nakryiko
2020-08-13  7:17 ` [PATCH bpf 6/9] libbpf: enforce 64-bitness of BTF for BPF object files Andrii Nakryiko
2020-08-13  7:17 ` [PATCH bpf 7/9] selftests/bpf: correct various core_reloc 64-bit assumptions Andrii Nakryiko
2020-08-13  7:17 ` Andrii Nakryiko [this message]
2020-08-13  7:17 ` [PATCH bpf 9/9] selftests/bpf: make test_varlen work with 32-bit user-space arch Andrii Nakryiko
2020-08-13 19:20 ` [PATCH bpf 0/9] Fix various issues with 32-bit libbpf Alexei Starovoitov
2020-08-13 20:03   ` Andrii Nakryiko

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