diff mbox series

btf_encoder: Align .BTF section to 8 bytes

Message ID 20210204151127.2676041-1-gprocida@google.com (mailing list archive)
State Not Applicable
Delegated to: BPF
Headers show
Series btf_encoder: Align .BTF section to 8 bytes | expand

Checks

Context Check Description
netdev/tree_selection success Not a local patch

Commit Message

Giuliano Procida Feb. 4, 2021, 3:11 p.m. UTC 
This is to avoid misaligned access to BTF type structs when
memory-mapping ELF sections.

Signed-off-by: Giuliano Procida <gprocida@google.com>
---
 libbtf.c | 9 +++++++++
 1 file changed, 9 insertions(+)
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Patch

diff --git a/libbtf.c b/libbtf.c
index 5b91d3a..9974747 100644
--- a/libbtf.c
+++ b/libbtf.c
@@ -740,6 +740,14 @@  static int btf_elf__write(const char *filename, struct btf *btf)
 		goto out;
 	}
 
+	/*
+	 * We'll align .BTF to 8 bytes to cater for all architectures. It'd be
+	 * nice if we could fetch this value from somewhere. The BTF
+	 * specification does not discuss alignment and its trailing string
+	 * table is not currently padded to any particular alignment.
+	 */
+	const size_t btf_alignment = 8;
+
 	/*
 	 * First we check if there is already a .BTF section present.
 	 */
@@ -823,6 +831,7 @@  static int btf_elf__write(const char *filename, struct btf *btf)
 			__func__, elf_errmsg(elf_errno()));
 		goto out;
 	}
+	btf_shdr->sh_addralign = btf_alignment;
 	btf_shdr->sh_entsize = 0;
 	btf_shdr->sh_flags = SHF_ALLOC;
 	if (dot_btf_offset)