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[dwarves,v4,5/5] btf_encoder: Align .BTF section to 8 bytes

Message ID 20210217110804.75923-6-gprocida@google.com (mailing list archive)
State Not Applicable
Delegated to: BPF
Headers show
Series ELF writing changes | expand

Checks

Context Check Description
netdev/tree_selection success Not a local patch

Commit Message

Giuliano Procida Feb. 17, 2021, 11:08 a.m. UTC 
This is to avoid misaligned access to BTF type structs when
memory-mapping ELF objects.

Acked-by: Andrii Nakryiko <andrii@kernel.org>
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 9ff03ca..ee677fa 100644
--- a/libbtf.c
+++ b/libbtf.c
@@ -744,6 +744,14 @@  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.
 	 */
@@ -821,6 +829,7 @@  static int btf_elf__write(const char *filename, struct btf *btf)
 		elf_error("elf_getshdr(btf_scn) failed");
 		goto out;
 	}
+	btf_shdr.sh_addralign = btf_alignment;
 	btf_shdr.sh_entsize = 0;
 	btf_shdr.sh_flags = 0;
 	if (dot_btf_offset)