[all-commits] [llvm/llvm-project] 9271ca: [BPF] use base lvalue type for preserve_{struct, un...

[yonghong-song via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 9271cab270a52b5200ef45a16f1a9d9baaccaba0
      https://github.com/llvm/llvm-project/commit/9271cab270a52b5200ef45a16f1a9d9baaccaba0
  Author: Yonghong Song <yhs at fb.com>
  Date:   2020-02-04 (Tue, 04 Feb 2020)

  Changed paths:
    M clang/lib/CodeGen/CGExpr.cpp
    A clang/test/CodeGen/builtin-preserve-access-index-typedef.c

  Log Message:
  -----------
  [BPF] use base lvalue type for preserve_{struct,union}_access_index metadata

Linux commit
  https://github.com/torvalds/linux/commit/1cf5b23988ea0086a252a5c8b005b075f1e9b030#diff-289313b9fec99c6f0acfea19d9cfd949
uses "#pragma clang attribute push (__attribute__((preserve_access_index)),
      apply_to = record)"
to apply CO-RE relocations to all records including the following pattern:
  #pragma clang attribute push (__attribute__((preserve_access_index)), apply_to = record)
  typedef struct {
    int a;
  } __t;
  #pragma clang attribute pop
  int test(__t *arg) { return arg->a; }

The current approach to use struct type in the relocation record will
result in an anonymous struct, which make later type matching difficult
    in bpf loader. In fact, current BPF backend will fail the above program
with assertion:
  clang: ../lib/Target/BPF/BPFAbstractMemberAccess.cpp:796: ...
     Assertion `TypeName.size()' failed.

The patch use the base lvalue type for the "base" value to annotate
preservee_{struct,union}_access_index intrinsics. In the above example,
the type will be "__t" which preserved the type name.

Differential Revision: https://reviews.llvm.org/D73900