[all-commits] [llvm/llvm-project] dc1c43: [BPF] Add BTF 64bit enum value support

[yonghong-song via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: dc1c43d726c87e18fae33cb26f2cd05dbd1fdfa5
      https://github.com/llvm/llvm-project/commit/dc1c43d726c87e18fae33cb26f2cd05dbd1fdfa5
  Author: Yonghong Song <yhs at fb.com>
  Date:   2022-06-06 (Mon, 06 Jun 2022)

  Changed paths:
    M llvm/lib/Target/BPF/BTF.def
    M llvm/lib/Target/BPF/BTF.h
    M llvm/lib/Target/BPF/BTFDebug.cpp
    M llvm/lib/Target/BPF/BTFDebug.h
    M llvm/test/CodeGen/BPF/BTF/enum-basic.ll
    M llvm/test/CodeGen/BPF/CORE/intrinsic-typeinfo-enum-value-opaque-pointer.ll
    M llvm/test/CodeGen/BPF/CORE/intrinsic-typeinfo-enum-value.ll

  Log Message:
  -----------
  [BPF] Add BTF 64bit enum value support

Current BTF only supports 32-bit value. For example,
  enum T { VAL = 0xffffFFFF00000008 };
the generated BTF looks like
        .long   16                              # BTF_KIND_ENUM(id = 4)
        .long   100663297                       # 0x6000001
        .long   8
        .long   18
        .long   8
The encoded value is 8 which equals to (uint32_t)0xffffFFFF00000008
and this is incorrect.

This patch introduced BTF_KIND_ENUM64 which permits to encode
64-bit value. The format for each enumerator looks like:
        .long   name_offset
        .long   (uint32_t)value # lower-32 bit value
        .long   value >> 32     # high-32 bit value

We use two 32-bit values to represent a 64-bit value as current
BTF type subsection has 4-byte alignment and gaps are not permitted
in the subsection.

This patch also added support for kflag (the bit 31 of CommonType.Info)
such that kflag = 1 implies the value is signed and kflag = 0
implies the value is unsigned. The kernel UAPI enumerator definition is
  struct btf_enum {
        __u32   name_off;
        __s32   val;
  };
so kflag = 0 with unsigned value provides backward compatability.

With this patch, for
  enum T { VAL = 0xffffFFFF00000008 };
the generated BTF looks like
        .long   16                              # BTF_KIND_ENUM64(id = 4)
        .long   3187671053                      # 0x13000001
        .long   8
        .long   18
        .long   8                               # 0x8
        .long   4294967295                      # 0xffffffff
and the enumerator value and signedness are encoded correctly.

Differential Revision: https://reviews.llvm.org/D124641