Message-ID: <CA+icZUVDVchAbxxnpYK3Qcg4aLk_diF=wgrqj5xXuKOp95Zv-w@mail.gmail.com>
Date:   Sat, 6 Feb 2021 21:46:10 +0100
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Yonghong Song <yhs@...com>
Cc:     Mark Wieelard <mark@...mp.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
        dwarves@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        bpf@...r.kernel.org, Jiri Olsa <jolsa@...nel.org>,
        Jan Engelhardt <jengelh@...i.de>,
        Domenico Andreoli <cavok@...ian.org>,
        Matthias Schwarzott <zzam@...too.org>,
        Andrii Nakryiko <andriin@...com>,
        Paul Moore <paul@...l-moore.com>,
        Ondrej Mosnacek <omosnace@...hat.com>,
        Daniel P. Berrangé <berrange@...hat.com>,
        Tom Stellard <tstellar@...hat.com>,
        Fangrui Song <maskray@...gle.com>
Subject: Re: ERROR: INT DW_ATE_unsigned_1 Error emitting BTF type

On Sat, Feb 6, 2021 at 9:13 PM Yonghong Song <yhs@...com> wrote:
>
>
>
> On 2/6/21 11:44 AM, Sedat Dilek wrote:
> > On Sat, Feb 6, 2021 at 8:33 PM Yonghong Song <yhs@...com> wrote:
> >>
> >>
> >>
> >> On 2/6/21 11:28 AM, Sedat Dilek wrote:
> >>> On Sat, Feb 6, 2021 at 8:22 PM Sedat Dilek <sedat.dilek@...il.com> wrote:
> >>>>
> >>>> On Sat, Feb 6, 2021 at 8:17 PM Yonghong Song <yhs@...com> wrote:
> >>>>>
> >>>>>
> >>>>>
> >>>>> On 2/6/21 10:10 AM, Sedat Dilek wrote:
> >>>>>> On Sat, Feb 6, 2021 at 6:53 PM Yonghong Song <yhs@...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?
> >>>>>
> >>>>> I just sent out a patch. You are cc'ed. I also attached in this email.
> >>>>> Yes, it would be great if you can upload mlx5_core.ko so I can
> >>>>> double check with this DW_ATE_unsigned_160 which is really usual.
> >>>>>
> >>>>
> >>>> Yupp, just built a new pahole :-).
> >>>> Re-building linux-kernel...
> >>>>
> >>>> Will upload mlx5_core.ko - need zstd-ed it before.
> >>>>
> >>>
> >>> Hmm, I guess you want a mlx5_core.ko with your patch applied-to-pahole-1.20 :-)?
> >>
> >> this should work too. I want to check dwarf data. My patch won't impact
> >> dwarf generation.
> >>
> >
> > Usual Dropbox-Link:
> >
> > https://www.dropbox.com/sh/kvyh8ps7na0r1h5/AABfyNfDZ2bESse_bo4h05fFa?dl=0
> >
> > See "for-yhs" directory:
> >
> > 1. mlx5-module_yhs-v1 ("[PATCH dwarves] btf_encoder: sanitize
> > non-regular int base type")
> > 2. mlx5-module_yhs-dileks-v4 (with the last diff-v4 I tried successfully)
>
> Thanks, with llvm-dwarfdump, I can see
>
> 0x00d65616:   DW_TAG_base_type
>                  DW_AT_name      ("DW_ATE_unsigned_160")
>                  DW_AT_encoding  (DW_ATE_unsigned)
>                  DW_AT_byte_size (0x14)
>
> 0x00d88e81:         DW_TAG_variable
>                        DW_AT_location    (indexed (0xad) loclist =
> 0x0005df42:
>                           [0x0000000000088c8e, 0x0000000000088c97):
> DW_OP_breg9 R9+0, DW_OP_convert (0x00d65616) "DW_ATE_unsigned_160",
> DW_OP_convert (0x00d65607) "DW_ATE_unsigned_32", DW_OP_stack_value,
> DW_OP_piece 0x4)
>                        DW_AT_abstract_origin     (0x00d88d37 "_v")
>
>
> 0x00d88d37:       DW_TAG_variable
>                      DW_AT_name  ("_v")
>                      DW_AT_decl_file
> ("/home/dileks/src/linux-kernel/git/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_ste.c")
>                      DW_AT_decl_line     (1198)
>                      DW_AT_type  (0x00d68835 "u32")
>
> The source code at line 1198.
> 1198         DR_STE_SET_MASK_V(eth_l3_ipv4_5_tuple, bit_mask,
> 1199                           source_port, mask, udp_sport);
>
> This is for struct mlx5dr_match_spec.
>
> struct mlx5dr_match_spec {
>          u32 smac_47_16;         /* Source MAC address of incoming packet */
>          /* Incoming packet Ethertype - this is the Ethertype
>           * following the last VLAN tag of the packet
>           */
>          u32 ethertype:16;
>          u32 smac_15_0:16;
> ...
>          u32 tcp_dport:16;
>          /* TCP source port.;tcp and udp sport/dport are mutually
> exclusive */
>          u32 tcp_sport:16;
>          u32 ttl_hoplimit:8;
>          u32 reserved:24;
>          /* UDP destination port.;tcp and udp sport/dport are mutually
> exclusive */
>          u32 udp_dport:16;
>          /* UDP source port.;tcp and udp sport/dport are mutually
> exclusive */
>          u32 udp_sport:16;
>          /* IPv6 source address of incoming packets
>           * For IPv4 address use bits 31:0 (rest of the bits are reserved)
>           * This field should be qualified by an appropriate ethertype
>           */
>          u32 src_ip_127_96;
> ...
> }
>
> which includes a bunch of bit fields and non-bit fields.
>
> I have no idea why clang will generate
>     DW_OP_convert (0x00d65616) "DW_ATE_unsigned_160"
> and possibly try to capture more semantic information?
> But BTF should be able to safely ignore this as described
> in my patch.
>
> Thanks.
>

[ CC Fangrui - the only guy I know who might comment on this ]

Fangrui, feel free to comment?

Get the patch "[PATCH dwarves] btf_encoder: sanitize non-regular int
base type" from Yonghong Son:

link="https://lore.kernel.org/r/20210206191350.830616-1-yhs@fb.com"
b4 -d am $link

I commented the success in the other thread.
Sorry for cross-posting.

Big Thank-You Yonghong!

- Sedat -


- Sedat -

> >
> > - Sedat -
> >
> >>>
> >>>> - Sedat -
> >>>>
> >>>>>>
> >>>>>> 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 -
> >>>>>>

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