Alan Maguire <alan.maguire@xxxxxxxxxx> 于2024年6月26日周三 18:19写道： > > On 26/06/2024 08:29, Totoro W wrote: > > Hi folks, > > > > This is my first time to ask questions in this mailing list. I'm the > > author of https://github.com/tw4452852/zbpf which is a framework to > > write BPF programs with Zig toolchain. > > During the development, as the BTF is totally generated by the Zig > > toolchain, some naming conventions will make the BTF verifier refuse > > to load. > > Right now I have to patch the libbpf to do some fixup before loading > > into the kernel > > (https://github.com/tw4452852/libbpf_zig/blob/main/0001-temporary-WA-for-invalid-BTF-info-generated-by-Zig.patch). > > Even though this just work-around the issue, I'm still curious about > > the current naming sanitation, I want to know some background about > > it. > > If possible, could we relax this to accept more languages (like Zig) > > to write BPF programs? Thanks in advance. > > > > For reference, here the BTF generated by Zig for this program > > (https://github.com/tw4452852/zbpf/blob/main/samples/perf_event.zig) > > > > [1] PTR '*[4]u8' type_id=3 > > The problem here as Eduard mentioned is that the zig compiler appears to > be generating unneeded names for pointers, and then you're working > around this in zbpf, is that right? Yes, you're right, I kind of workaround this issue in zbpf. > It's not clear to me what that > pointer name adds - I suspect it's saying it's a pointer to an array of > 4 u8s, but we get that from the fact it's a PTR to type_id 3 - an ARRAY > with element type 'u8' (type id 2) and nr_elems=4, no name is needed. So > the name doesn't add any information it seems; or at least the info the > name provides can be reconstructed from the BTF without having the name. Your guess is right. > > So the root problem here appears to be the zig compiler's BTF > generation. If there are some language constraints that require some > sort of name annotation for pointers, couldn't that be done via BTF type > tags or via some other compatible mechanism? > > So I think we need to understand whether the BTF incompatibilities arise > due to genuine language features or if they are the result of > incorrectly-generated BTF during zig compilation. I dug around a bit in > the zig github repo but could only find BTF parsing code, not code for > BTF generation. Finding where the BTF is generated in the zig toolchain > and understanding why it is generating names for pointers is the first > step here I think. Currently, for the BPF platform, Zig uses LLVM as backend. So the BTF generation is done by LLVM (https://github.com/llvm/llvm-project/blob/37eb9c9632fb5e82827d1a0559f2279e9a9f1969/llvm/lib/Target/BPF/BTFDebug.cpp) with debug meta information provided by the Zig toolchain (https://github.com/ziglang/zig/blob/master/src/codegen/llvm.zig) > > Alan > > > > [2] INT 'u8' size=1 bits_offset=0 nr_bits=8 encoding=(none) > > [3] ARRAY '(anon)' type_id=2 index_type_id=4 nr_elems=4 > > [4] INT '__ARRAY_SIZE_TYPE__' size=4 bits_offset=0 nr_bits=32 encoding=(none) > > [5] PTR '*u32' type_id=6 > > [6] INT 'u32' size=4 bits_offset=0 nr_bits=32 encoding=(none) > > [7] STRUCT 'map.Map.Def' size=24 vlen=3 > > 'type' type_id=1 bits_offset=0 > > 'key' type_id=5 bits_offset=64 > > 'value' type_id=5 bits_offset=128 > > [8] VAR 'events' type_id=7, linkage=global > > [9] PTR '*[2]u8' type_id=10 > > [10] ARRAY '(anon)' type_id=2 index_type_id=4 nr_elems=2 > > [11] PTR '*[1]u8' type_id=12 > > [12] ARRAY '(anon)' type_id=2 index_type_id=4 nr_elems=1 > > [13] STRUCT 'map.Map.Def' size=32 vlen=4 > > 'type' type_id=9 bits_offset=0 > > 'key' type_id=5 bits_offset=64 > > 'value' type_id=5 bits_offset=128 > > 'max_entries' type_id=11 bits_offset=192 > > [14] VAR 'my_pid' type_id=13, linkage=global > > [15] FUNC_PROTO '(anon)' ret_type_id=16 vlen=1 > > '(anon)' type_id=17 > > [16] INT 'c_int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED > > [17] PTR '*perf_event.test_perf_event_array__opaque_478' type_id=18 > > [18] STRUCT 'perf_event.test_perf_event_array__opaque_478' size=0 vlen=0 > > [19] FUNC 'test_perf_event_array' type_id=15 linkage=global > > [20] FUNC_PROTO '(anon)' ret_type_id=21 vlen=1 > > '(anon)' type_id=21 > > [21] INT 'usize' size=8 bits_offset=0 nr_bits=64 encoding=(none) > > [22] FUNC 'getauxvalImpl' type_id=20 linkage=global > > [23] ARRAY '(anon)' type_id=2 index_type_id=4 nr_elems=3 > > [24] VAR '_license' type_id=23, linkage=global > > [25] DATASEC '.maps' size=0 vlen=2 > > type_id=8 offset=0 size=24 (VAR 'events') > > type_id=14 offset=0 size=32 (VAR 'my_pid') > > [26] DATASEC 'license' size=0 vlen=1 > > type_id=24 offset=0 size=4 (VAR '_license') > > > > > > Regards. > >
