Re: [PATCH dwarves v2] btf_encoder: sanitize non-regular int base type

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Mon, Feb 08, 2021 at 11:22:48AM -0800, Nick Desaulniers escreveu:
> On Sat, Feb 6, 2021 at 11:17 PM Yonghong Song <yhs@fb.com> wrote:
> >
> > clang with dwarf5 may generate non-regular int base type,
> > i.e., not a signed/unsigned char/short/int/longlong/__int128.
> > Such base types are often used to describe
> > how an actual parameter or variable is generated. For example,
> >
> > 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")
> >
> > What it does is with a literal "0", did a "not" operation, and the converted to
> > one-bit unsigned int and then 8-bit unsigned int.
> >
> > Another example,
> >
> > 0x000e97e4:   DW_TAG_base_type
> >                 DW_AT_name      ("DW_ATE_unsigned_24")
> >                 DW_AT_encoding  (DW_ATE_unsigned)
> >                 DW_AT_byte_size (0x03)
> >
> > 0x000f88f8:     DW_TAG_variable
> >                   DW_AT_location        (indexed (0x3c) loclist = 0x00008fb0:
> >                      [0xffffffff82808812, 0xffffffff82808817):
> >                          DW_OP_breg0 RAX+0,
> >                          DW_OP_convert (0x000e97d5) "DW_ATE_unsigned_64",
> >                          DW_OP_convert (0x000e97df) "DW_ATE_unsigned_8",
> >                          DW_OP_stack_value,
> >                          DW_OP_piece 0x1,
> >                          DW_OP_breg0 RAX+0,
> >                          DW_OP_convert (0x000e97d5) "DW_ATE_unsigned_64",
> >                          DW_OP_convert (0x000e97da) "DW_ATE_unsigned_32",
> >                          DW_OP_lit8,
> >                          DW_OP_shr,
> >                          DW_OP_convert (0x000e97da) "DW_ATE_unsigned_32",
> >                          DW_OP_convert (0x000e97e4) "DW_ATE_unsigned_24",
> >                          DW_OP_stack_value,
> >                          DW_OP_piece 0x3
> >                      ......
> >
> > At one point, a right shift by 8 happens and the result is converted to
> > 32-bit unsigned int and then to 24-bit unsigned int.
> >
> > BTF does not need any of these DW_OP_* information and such non-regular int
> > types will cause libbpf to emit errors.
> > Let us sanitize them to generate BTF acceptable to libbpf and kernel.
> >
> > Cc: Sedat Dilek <sedat.dilek@gmail.com>
> > Acked-by: Andrii Nakryiko <andrii@kernel.org>
> > Signed-off-by: Yonghong Song <yhs@fb.com>
> 
> Thanks for the patch!
> 
> Tested-by: Nick Desaulniers <ndesaulniers@google.com>

Thanks for testing and documenting that you tested, added the tag to
the commit,

- Arnaldo