linux-kernel - Re: ERROR: INT DW_ATE_unsigned

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Message-ID: <CA+icZUV98seJrpNcSPvN_Vjc4Znc72zH3czqirnie80BGAQfEQ@mail.gmail.com>
Date:   Sat, 6 Feb 2021 08:26:02 +0100
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Yonghong Song <yhs@...com>
Cc:     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>,
        Mark Wieelard <mjw@...hat.com>,
        Paul Moore <paul@...l-moore.com>,
        Ondrej Mosnacek <omosnace@...hat.com>,
        Daniel P. Berrangé <berrange@...hat.com>,
        Tom Stellard <tstellar@...hat.com>
Subject: Re: ERROR: INT DW_ATE_unsigned_1 Error emitting BTF type

On Fri, Feb 5, 2021 at 9:03 PM Yonghong Song <yhs@...com> wrote:
>
>
>
> On 2/5/21 11:24 AM, Arnaldo Carvalho de Melo wrote:
> > Em Fri, Feb 05, 2021 at 11:10:08AM -0800, Yonghong Song escreveu:
> >> On 2/5/21 11:06 AM, Sedat Dilek wrote:
> >>> On Fri, Feb 5, 2021 at 7:53 PM Sedat Dilek <sedat.dilek@...il.com> wrote:
> >>> Grepping through linux.git/tools I guess some BTF tools/libs need to
> >>> know what BTF_INT_UNSIGNED is?
> >
> >> BTF_INT_UNSIGNED needs kernel support. Maybe to teach pahole to
> >> ignore this for now until kernel infrastructure is ready.
> >
> > Yeah, I thought about doing that.
> >
> >> Not sure whether this information will be useful or not
> >> for BTF. This needs to be discussed separately.
> >
> > Maybe search for the rationale for its introduction in DWARF.
>
> In LLVM, we have:
>    uint8_t BTFEncoding;
>    switch (Encoding) {
>    case dwarf::DW_ATE_boolean:
>      BTFEncoding = BTF::INT_BOOL;
>      break;
>    case dwarf::DW_ATE_signed:
>    case dwarf::DW_ATE_signed_char:
>      BTFEncoding = BTF::INT_SIGNED;
>      break;
>    case dwarf::DW_ATE_unsigned:
>    case dwarf::DW_ATE_unsigned_char:
>      BTFEncoding = 0;
>      break;
>
> I think DW_ATE_unsigned can be ignored in pahole since
> the default encoding = 0. A simple comment is enough.
>

For the followers (here: LLVM v12.0.0-rc1):

[ llvm/lib/Target/BPF/BTFDebug.cpp ]

BTFTypeInt::BTFTypeInt(uint32_t Encoding, uint32_t SizeInBits,
                       uint32_t OffsetInBits, StringRef TypeName)
    : Name(TypeName) {
  // Translate IR int encoding to BTF int encoding.
  uint8_t BTFEncoding;
  switch (Encoding) {
  case dwarf::DW_ATE_boolean:
    BTFEncoding = BTF::INT_BOOL;
    break;
  case dwarf::DW_ATE_signed:
  case dwarf::DW_ATE_signed_char:
    BTFEncoding = BTF::INT_SIGNED;
    break;
  case dwarf::DW_ATE_unsigned:
  case dwarf::DW_ATE_unsigned_char:
    BTFEncoding = 0;
    break;
  default:
    llvm_unreachable("Unknown BTFTypeInt Encoding");
  }

- Sedat -