[PATCH dwarves v3 5/5] btf_encoder: Align .BTF section to 8 bytes

[Giuliano Procida <gprocida@google.com>]

This is to avoid misaligned access to BTF type structs when
memory-mapping ELF objects.

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

diff --git a/libbtf.c b/libbtf.c
index 9f4abb3..6754a17 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)
-- 
2.30.0.478.g8a0d178c01-goog