On 6/16/21 2:25 AM, Tony Ambardar wrote:
While patching the .BTF_ids section in vmlinux, resolve_btfids writes type
ids using host-native endianness, and relies on libelf for any required
translation when finally updating vmlinux. However, the default type of the
.BTF_ids section content is ELF_T_BYTE (i.e. unsigned char), and undergoes
no translation. This results in incorrect patched values if cross-compiling
to non-native endianness, and can manifest as kernel Oops and test failures
which are difficult to debug.
Explicitly set the type of patched data to ELF_T_WORD, allowing libelf to
transparently handle the endian conversions.
Fixes: fbbb68de80a4 ("bpf: Add resolve_btfids tool to resolve BTF IDs in ELF object")
Cc: stable@xxxxxxxxxxxxxxx # v5.10+
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Yonghong Song <yhs@xxxxxx>
Link: https://lore.kernel.org/bpf/CAPGftE_eY-Zdi3wBcgDfkz_iOr1KF10n=9mJHm1_a_PykcsoeA@xxxxxxxxxxxxxx/
Signed-off-by: Tony Ambardar <Tony.Ambardar@xxxxxxxxx>
---
tools/bpf/resolve_btfids/main.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/tools/bpf/resolve_btfids/main.c b/tools/bpf/resolve_btfids/main.c
index d636643ddd35..f32c059fbfb4 100644
--- a/tools/bpf/resolve_btfids/main.c
+++ b/tools/bpf/resolve_btfids/main.c
@@ -649,6 +649,9 @@ static int symbols_patch(struct object *obj)
if (sets_patch(obj))
return -1;
+ /* Set type to ensure endian translation occurs. */
+ obj->efile.idlist->d_type = ELF_T_WORD;
The change makes sense to me as .BTF_ids contains just a list of
u32's.
Jiri, could you double check on this?
+
elf_flagdata(obj->efile.idlist, ELF_C_SET, ELF_F_DIRTY);
err = elf_update(obj->efile.elf, ELF_C_WRITE);
