On 5/11/22 5:32 PM, Andrii Nakryiko wrote:
On Wed, May 11, 2022 at 3:02 PM Yonghong Song <yhs@xxxxxx> wrote:
With latest llvm15 built kernel (make -j LLVM=1), I hit the following
error when build selftests (make -C tools/testing/selftests/bpf -j LLVM=1):
In file included from skeleton/pid_iter.bpf.c:3:
.../selftests/bpf/tools/build/bpftool/vmlinux.h:84050:9: error: unknown type name
'__builtin_va_list___2'; did you mean '__builtin_va_list'?
typedef __builtin_va_list___2 va_list___2;
^~~~~~~~~~~~~~~~~~~~~
__builtin_va_list
note: '__builtin_va_list' declared here
In file included from skeleton/profiler.bpf.c:3:
.../selftests/bpf/tools/build/bpftool/vmlinux.h:84050:9: error: unknown type name
'__builtin_va_list__ _2'; did you mean '__builtin_va_list'?
typedef __builtin_va_list___2 va_list___2;
^~~~~~~~~~~~~~~~~~~~~
__builtin_va_list
note: '__builtin_va_list' declared here
The error can be easily explained with after-dedup vmlinux btf:
[21] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED
[2300] STRUCT '__va_list_tag' size=24 vlen=4
'gp_offset' type_id=2 bits_offset=0
'fp_offset' type_id=2 bits_offset=32
'overflow_arg_area' type_id=32 bits_offset=64
'reg_save_area' type_id=32 bits_offset=128
[2308] TYPEDEF 'va_list' type_id=2309
[2309] TYPEDEF '__builtin_va_list' type_id=2310
[2310] ARRAY '(anon)' type_id=2300 index_type_id=21 nr_elems=1
[5289] PTR '(anon)' type_id=2308
[158520] STRUCT 'warn_args' size=32 vlen=2
'fmt' type_id=14 bits_offset=0
'args' type_id=2308 bits_offset=64
[27299] INT '__ARRAY_SIZE_TYPE__' size=4 bits_offset=0 nr_bits=32 encoding=(none)
[34590] TYPEDEF '__builtin_va_list' type_id=34591
[34591] ARRAY '(anon)' type_id=2300 index_type_id=27299 nr_elems=1
The typedef __builtin_va_list is a builtin type for the compiler.
In the above case, two typedef __builtin_va_list are generated.
The reason is due to different array index_type_id. This happened
when pahole is running with more than one jobs when parsing dwarf
and generating btfs.
Function btf_encoder__encode_cu() is used to do btf encoding for
each cu. The function will try to find an "int" type for the cu
if it is available, otherwise, it will create a special type
with name __ARRAY_SIZE_TYPE__. For example,
file1: yes 'int' type
file2: no 'int' type
In serial mode, file1 is processed first, followed by file2.
both will have 'int' type as the array index type since file2
will inherit the index type from file1.
In parallel mode though, arrays in file1 will have index type 'int',
and arrays in file2 wil have index type '__ARRAY_SIZE_TYPE__'.
This will prevent some legitimate dedup and may have generated
vmlinux.h having compilation error.
I think it is two separate problems.
1. Maybe instead of this generating __ARRAY_SIZE_TYPE__ we should
generate proper 'int' type?
This should work. Will post v2 with this.
2. __builtin_va_list___2 shouldn't have happened, it's libbpf bug.
Libbpf handles __builtin_va_list specially (see
btf_dump_is_blacklisted()), so we need to fix libbpf to not get
confused if there are two __builtin_va_list copies in BTF.
I checked code. the libbpf prevents generating
typedef <...> __builtin_va_list
since __builtin_va_list is a builtin type.
Here, due to __ARRAY_SIZE_TYPE__ problem, the following are generated
in vmlinux.h.
typedef __builtin_va_list va_list;
typedef __builtin_va_list___2 va_list___2;
since __builtin_va_list appears twice in the BTF.
But due to the libbpf implementation to skip
typedef <...> __builtin_va_list
We don't have __builtin_va_list___2 defined and this
caused compilation error.
Although we could workaround the issue in libbpf
such that if the typedef is in the format of
typedef __builtin_va_list<...> <other_type>
we should just emit
typedef __builtin_va_list <other_type>
But fixing the issue in pahole is much better since
we won't have va_list___2 any more.
This patch fixed the issue by normalizing all array_index types
to be the first array_index type in the whole btf.
Signed-off-by: Yonghong Song <yhs@xxxxxx>
---
btf_encoder.c | 24 +++++++++++++++++++++---
btf_encoder.h | 2 +-
pahole.c | 2 +-
3 files changed, 23 insertions(+), 5 deletions(-)
[...]
