On Sat, Feb 6, 2021 at 6:53 PM Yonghong Song <yhs@xxxxxx> wrote: > > > > On 2/6/21 8:24 AM, Mark Wieelard wrote: > > Hi, > > > > On Sat, Feb 06, 2021 at 12:26:44AM -0800, Yonghong Song wrote: > >> With the above vmlinux, the issue appears to be handling > >> DW_ATE_signed_1, DW_ATE_unsigned_{1,24,40}. > >> > >> The following patch should fix the issue: > > > > That doesn't really make sense to me. Why is the compiler emitting a > > DW_TAG_base_type that needs to be interpreted according to the > > DW_AT_name attribute? > > > > If the issue is that the size of the base type cannot be expressed in > > bytes then the DWARF spec provides the following option: > > > > If the value of an object of the given type does not fully occupy > > the storage described by a byte size attribute, the base type > > entry may also have a DW_AT_bit_size and a DW_AT_data_bit_offset > > attribute, both of whose values are integer constant values (see > > Section 2.19 on page 55). The bit size attribute describes the > > actual size in bits used to represent values of the given > > type. The data bit offset attribute is the offset in bits from the > > beginning of the containing storage to the beginning of the > > value. Bits that are part of the offset are padding. If this > > attribute is omitted a default data bit offset of zero is assumed. > > > > Would it be possible to use that encoding of those special types? If > > I agree with you. I do not like comparing me as well. Unfortunately, > there is no enough information in dwarf to find out actual information. > The following is the dwarf dump with vmlinux (Sedat provided) for > DW_ATE_unsigned_1. > > 0x000e97e9: DW_TAG_base_type > DW_AT_name ("DW_ATE_unsigned_1") > DW_AT_encoding (DW_ATE_unsigned) > DW_AT_byte_size (0x00) > > There is no DW_AT_bit_size and DW_AT_bit_offset for base type. > AFAIK, these two attributes typically appear in struct/union members > together with DW_AT_byte_size. > > Maybe compilers (clang in this case) can emit DW_AT_bit_size = 1 > and DW_AT_bit_offset = 0/7 (depending on big/little endian) and > this case, we just test and get DW_AT_bit_size and it should work. > > But I think BTF does not need this (DW_ATE_unsigned_1) for now. > I checked dwarf dump and it is mostly used for some arith operation > encoded in dump (in this case, e.g., shift by 1 bit) > > 0x000015cf: DW_TAG_base_type > DW_AT_name ("DW_ATE_unsigned_1") > DW_AT_encoding (DW_ATE_unsigned) > DW_AT_byte_size (0x00) > > 0x00010ed9: DW_TAG_formal_parameter > DW_AT_location (DW_OP_lit0, DW_OP_not, > DW_OP_convert (0x000015cf) "DW_ATE_unsigned_1", DW_OP_convert > (0x000015d4) "DW_ATE_unsigned_8", DW_OP_stack_value) > DW_AT_abstract_origin (0x00013984 "branch") > > Look at clang frontend, only the following types are encoded with > unsigned dwarf type. > > case BuiltinType::UShort: > case BuiltinType::UInt: > case BuiltinType::UInt128: > case BuiltinType::ULong: > case BuiltinType::WChar_U: > case BuiltinType::ULongLong: > Encoding = llvm::dwarf::DW_ATE_unsigned; > break; > > > > not, can we try to come up with some extension that doesn't require > > consumers to match magic names? > > You want me to upload mlx5_core.ko? When looking with llvm-dwarf for DW_ATE_unsigned_160: 0x00d65616: DW_TAG_base_type DW_AT_name ("DW_ATE_unsigned_160") DW_AT_encoding (DW_ATE_unsigned) DW_AT_byte_size (0x14) If you need further information, please let me know. Thanks. - Sedat -