On Fri, 2024-09-20 at 00:49 -0700, Tony Ambardar wrote:
While building of vmlinux employs a linker script to align the .BTF_ids section to 4 bytes, other usage leaves .BTF_ids unaligned and may lead to problems (e.g. [1]). Post-processing and libelf-based endian translation by resolve_btfids may also potentially suffer from misalignment.
Update encoding macros in btf_ids.h to always align BTF ID data to 4 bytes.
Signed-off-by: Tony Ambardar tony.ambardar@gmail.com
include/linux/btf_ids.h | 1 + 1 file changed, 1 insertion(+)
diff --git a/include/linux/btf_ids.h b/include/linux/btf_ids.h index c0e3e1426a82..c10b163dc340 100644 --- a/include/linux/btf_ids.h +++ b/include/linux/btf_ids.h @@ -89,6 +89,7 @@ word \ #define __BTF_ID_LIST(name, scope) \ asm( \ ".pushsection " BTF_IDS_SECTION ","a"; \n" \ +".balign 4, 0; \n" \ "." #scope " " #name "; \n" \ #name ":; \n" \ ".popsection; \n");
This forces all id list symbols to be aligned on 4 bytes. Should the same be done for __BTF_SET_START?
Also, is it guaranteed that all btf ids are organized in lists and sets? Grepping through the code it seems they are, but it looks like resolve_btfids does not really enforce this, simply looking for symbols matching a special name __BTF_ID__<type>__<symbol>[__<id>] .