On 3/4/21 8:41 AM, Yonghong Song wrote:
On 3/4/21 3:25 AM, Lorenz Bauer wrote:
Hi Yonghong, Andrii,
Some more poking at CO-RE. The code below leads to a compiler error:
struct s {
int _1;
char _2;
};
__section("socket_filter/type_ids") int type_ids() {
return bpf_core_type_id_kernel(const struct s);
}
Truncated output:
fatal error: error in backend: Empty type name for BTF_TYPE_ID_REMOTE
reloc
PLEASE submit a bug report to
https://bugs.llvm.org/
and include the
crash backtrace, preprocessed source, and associated run script.
Stack dump:
0. Program arguments: clang-12 -target bpf -O2 -g -Wall -Werror
-mlittle-endian -c internal/btf/testdata/relocs.c -o
internal/btf/testdata/relocs-el.elf
1. <eof> parser at end of file
2. Per-function optimization
3. Running pass 'BPF Preserve Debuginfo Type' on function '@type_ids'
...
clang: error: clang frontend command failed with exit code 70 (use -v
to see invocation)
Ubuntu clang version
12.0.0-++20210126113614+510b3d4b3e02-1~exp1~20210126104320.178
Target: bpf
"volatile" has the same problem. Interestingly, the same code works
for bpf_core_type_id_local. Is this expected?
First, bpf_core_type_id_local() works as compiler did not check type
name. for bpf_core_type_id_local(), there is no relocation, libbpf
may need to adjust type id if it tries to do btf dedup, merging, etc.
Second, the above bpf_core_type_id_kernel() failed due to
"const" (or "volatile") modifier. bpf_core_type_id_kernel()
requires a type name as relocation will be performed.
In the current implementation, the btf type is
const -> struct s
and there is no name for "const", that is why compiler issues
an explicit fatal error:
fatal error: error in backend: Empty type name for
BTF_TYPE_ID_REMOTE reloc
To fix the issue, just do not use any modifier,
bpf_core_type_id_kernel(struct s)
should work fine.
I think in the case, it would be good if the compiler tries
to peel off modifiers and find the ultimate type name
instead of fatal error. I will put a patch on this.
Lorenz, the issue has been fixed by llvm patch
https://reviews.llvm.org/D97986. It is in llvm13 trunk now.
I have also requested the fix to backport to 12.0.1 release.
Thanks!
Thanks for reporting!
Best
Lorenz
