On 4/23/24 6:15 AM, Xin Liu wrote:
On Mon, 22 Apr 2024 10:43:38 -0700 Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote:
On Mon, Apr 22, 2024 at 7:46 AM Xin Liu <liuxin350@xxxxxxxxxx> wrote:
In btf__add_int, the size of the new btf_kind_int type is limited.
When the size is greater than 16, btf__add_int fails to be added
and -EINVAL is returned. This is usually effective.
However, when the built-in type __builtin_aarch64_simd_xi in the
NEON instruction is used in the code in the arm64 system, the value
of DW_AT_byte_size is 64. This causes btf__add_int to fail to
properly add btf information to it.
like this:
...
<1><cf>: Abbrev Number: 2 (DW_TAG_base_type)
<d0> DW_AT_byte_size : 64 // over max size 16
<d1> DW_AT_encoding : 5 (signed)
<d2> DW_AT_name : (indirect string, offset: 0x53): __builtin_aarch64_simd_xi
<1><d6>: Abbrev Number: 0
...
An easier way to solve this problem is to treat it as a base type
and set byte_size to 64. This patch is modified along these lines.
Fixes: 4a3b33f8579a ("libbpf: Add BTF writing APIs")
Signed-off-by: Xin Liu <liuxin350@xxxxxxxxxx>
---
tools/lib/bpf/btf.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 2d0840ef599a..0af121293b65 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -1934,7 +1934,7 @@ int btf__add_int(struct btf *btf, const char *name, size_t byte_sz, int encoding
if (!name || !name[0])
return libbpf_err(-EINVAL);
/* byte_sz must be power of 2 */
- if (!byte_sz || (byte_sz & (byte_sz - 1)) || byte_sz > 16)
+ if (!byte_sz || (byte_sz & (byte_sz - 1)) || byte_sz > 64)
maybe we should just remove byte_sz upper limit? We can probably
imagine 256-byte integers at some point, so why bother artificially
restricting it?
pw-bot: cr
In the current definition of btf_kind_int, bits has only 8 bits, followed
by 8 bits of unused interval. When we expand, we should only use 16 bits
at most, so the maximum value should be 8192(1 << 16 / 8), directly removing
the limit of byte_sz. It may not fit the current design. For INT type btfs
greater than 255, how to dump is still a challenge.
Looking at this patch. Now I remember that I have an old pahole patch
to address similar issues
https://lore.kernel.org/bpf/20230426055030.3743074-1-yhs@xxxxxx/
which is not merged and I forgot that.
In that particular case, the int size is 1024 bytes.
Currently the int type more than 16 bytes cannot be dumped in libbpf.
Do you have a particular use case to use your__builtin_aarch64_simd_xi() type
in bpf program? I guess probably not as BPF does not support
builtin function your__builtin_aarch64_simd_xi().
Does the current version support a maximum of 8192 bytes?
return libbpf_err(-EINVAL);
if (encoding & ~(BTF_INT_SIGNED | BTF_INT_CHAR | BTF_INT_BOOL))
return libbpf_err(-EINVAL);
--
2.33.0
