On 4/26/23 11:09 AM, Nick Desaulniers wrote:
On Tue, Apr 25, 2023 at 10:50 PM Yonghong Song <yhs@xxxxxx> wrote:Nick Desaulniers reported an issue ([1]) where an 128-byte sized type (DW_ATE_unsigned_1024) cannot be encoded into BTF with failure message likes below: $ pahole -J reduced.o [2] INT DW_ATE_unsigned_1024 Error emitting BTF type Encountered error while encoding BTF. See [1] for how to reproduce the issue. The failure is due to currently BTF int type only supports upto 16 bytes (__int128) and in this case the dwarf int type is 128-byte. The DW_ATE_unsigned_1024 is not a normal type for variable/func declaration etc. It is used in DW_AT_location. There are two ways to resolve this issue. (1). If btf encoding is expected, remove all dwarf int types where btf encoding will failure, e.g., non-power-of-2 bytes, or greater than 16 bytes. (2). do a sanitization in btf_encoder ([2]). This patch uses method (2) since it is a simple fix in btf_encoder. I checked my local built vmlinux with latest bpf-next. There is only one instance of DW_ATE_unsigned_24 (used in DW_AT_location) so I expect irregular int types should be very rare. [1] https://github.com/libbpf/libbpf/pull/680 [2] commit 7d8e829f636f ("btf_encoder: Sanitize non-regular int base type") Signed-off-by: Yonghong Song <yhs@xxxxxx>Thanks, this fixed the above reported error for me. My report is just forwarded from Satya. Reported-by: Satya Durga Srinivasu Prabhala <quic_satyap@xxxxxxxxxxx> Tested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> I don't know if that change has other implications for unusual byte sizes. We might need to consider at some point waiting to validate DW_TAG_base_type until we know that they're not used outside of DW_AT_location expressions.
David Blaikie confirmed that indeed special types like DW_ATE_unsigned_1024 is indeed generated for DW_AT_location.
See https://github.com/libbpf/libbpf/pull/680 for details.
--- btf_encoder.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/btf_encoder.c b/btf_encoder.c index 65f6e71..1aa0ad0 100644 --- a/btf_encoder.c +++ b/btf_encoder.c @@ -394,7 +394,7 @@ static int32_t btf_encoder__add_base_type(struct btf_encoder *encoder, const str * these non-regular int types to avoid libbpf/kernel complaints. */ byte_sz = BITS_ROUNDUP_BYTES(bt->bit_size); - if (!byte_sz || (byte_sz & (byte_sz - 1))) { + if (!byte_sz || (byte_sz & (byte_sz - 1)) || byte_sz > 16) { name = "__SANITIZED_FAKE_INT__"; byte_sz = 4; } -- 2.34.1
