* bpf_core_type_id_kernel with qualifier aborts clang compilation
@ 2021-03-04 11:25 Lorenz Bauer
2021-03-04 16:41 ` Yonghong Song
0 siblings, 1 reply; 4+ messages in thread
From: Lorenz Bauer @ 2021-03-04 11:25 UTC (permalink / raw)
To: Yonghong Song, Andrii Nakryiko; +Cc: bpf
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?
Best
Lorenz
--
Lorenz Bauer | Systems Engineer
6th Floor, County Hall/The Riverside Building, SE1 7PB, UK
www.cloudflare.com
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: bpf_core_type_id_kernel with qualifier aborts clang compilation
2021-03-04 11:25 bpf_core_type_id_kernel with qualifier aborts clang compilation Lorenz Bauer
@ 2021-03-04 16:41 ` Yonghong Song
2021-03-05 21:36 ` Yonghong Song
0 siblings, 1 reply; 4+ messages in thread
From: Yonghong Song @ 2021-03-04 16:41 UTC (permalink / raw)
To: Lorenz Bauer, Andrii Nakryiko; +Cc: bpf
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.
Thanks for reporting!
>
> Best
> Lorenz
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: bpf_core_type_id_kernel with qualifier aborts clang compilation
2021-03-04 16:41 ` Yonghong Song
@ 2021-03-05 21:36 ` Yonghong Song
2021-03-08 9:33 ` Lorenz Bauer
0 siblings, 1 reply; 4+ messages in thread
From: Yonghong Song @ 2021-03-05 21:36 UTC (permalink / raw)
To: Lorenz Bauer, Andrii Nakryiko; +Cc: bpf
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
>>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: bpf_core_type_id_kernel with qualifier aborts clang compilation
2021-03-05 21:36 ` Yonghong Song
@ 2021-03-08 9:33 ` Lorenz Bauer
0 siblings, 0 replies; 4+ messages in thread
From: Lorenz Bauer @ 2021-03-08 9:33 UTC (permalink / raw)
To: Yonghong Song; +Cc: Andrii Nakryiko, bpf
On Fri, 5 Mar 2021 at 21:36, Yonghong Song <yhs@fb.com> wrote:
>
> 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 again for the quick fix :)
--
Lorenz Bauer | Systems Engineer
6th Floor, County Hall/The Riverside Building, SE1 7PB, UK
www.cloudflare.com
^ permalink raw reply [flat|nested] 4+ messages in thread
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2021-03-04 11:25 bpf_core_type_id_kernel with qualifier aborts clang compilation Lorenz Bauer
2021-03-04 16:41 ` Yonghong Song
2021-03-05 21:36 ` Yonghong Song
2021-03-08 9:33 ` Lorenz Bauer
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