On Wed, May 11, 2022 at 9:13 PM Yonghong Song <yhs@xxxxxx> wrote: > > > > 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. Sounds good, let's do it in pahole, thanks! > > > > >> 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(-) > >> > > > > [...]
