[PATCH] D124641: [BPF] Add BTF 64bit enum value support

[Yonghong Song via Phabricator via llvm-commits]

yonghong-song created this revision.
yonghong-song added reviewers: ast, anakryiko.
Herald added a subscriber: hiraditya.
Herald added a project: All.
yonghong-song requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

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   value >> 32     # high-32 bit value
  .long   (uint32_t)value # lower-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 unsigned and kflag = 0
implies the value is 0. The kernel UAPI enumerator definition is

  struct btf_enum { 
        __u32   name_off;                           
        __s32   val;
  };

so kflag = 0 with signed 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   2466250753                      # 0x93000001
  .long   8
  .long   18
  .long   4294967295                      # 0xffffffff
  .long   8                               # 0x8

and the enumerator value and signedness are encoded correctly.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D124641

Files:
  llvm/lib/Target/BPF/BTF.def
  llvm/lib/Target/BPF/BTF.h
  llvm/lib/Target/BPF/BTFDebug.cpp
  llvm/lib/Target/BPF/BTFDebug.h
  llvm/test/CodeGen/BPF/BTF/struct-enum.ll
  llvm/test/CodeGen/BPF/CORE/intrinsic-typeinfo-enum-value-opaque-pointer.ll
  llvm/test/CodeGen/BPF/CORE/intrinsic-typeinfo-enum-value.ll

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D124641.425918.patch
Type: text/x-patch
Size: 9220 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20220428/89b2c86d/attachment.bin>