lkml.org 
[lkml]   [2021]   [Feb]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: ERROR: INT DW_ATE_unsigned_1 Error emitting BTF type
On Sat, Feb 6, 2021 at 6:53 PM Yonghong Song <yhs@fb.com> 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 -

\
 
 \ /
  Last update: 2021-02-06 19:12    [W:0.073 / U:7.312 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site