[all-commits] [llvm/llvm-project] 2c8258: [dfsan] Use the sanitizer allocator to reduce memo...

[Z via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 2c82588dacac52ba8168214c6814ce22277d6e88
      https://github.com/llvm/llvm-project/commit/2c82588dacac52ba8168214c6814ce22277d6e88
  Author: Jianzhou Zhao <jianzhouzh at google.com>
  Date:   2021-06-06 (Sun, 06 Jun 2021)

  Changed paths:
    M compiler-rt/lib/dfsan/CMakeLists.txt
    M compiler-rt/lib/dfsan/dfsan.cpp
    M compiler-rt/lib/dfsan/dfsan.h
    M compiler-rt/lib/dfsan/dfsan_custom.cpp
    M compiler-rt/lib/dfsan/dfsan_interceptors.cpp
    A compiler-rt/lib/dfsan/dfsan_new_delete.cpp
    M compiler-rt/lib/dfsan/done_abilist.txt
    M compiler-rt/test/dfsan/custom.cpp
    A compiler-rt/test/dfsan/interceptors.c

  Log Message:
  -----------
  [dfsan] Use the sanitizer allocator to reduce memory cost

dfsan does not use sanitizer allocator as others. In practice,
we let it use glibc's allocator since tcmalloc needs more work
to be working with dfsan well. With glibc, we observe large
memory leakage. This could relate to two things:

1) glibc allocator has limitation: for example, tcmalloc can reduce memory footprint 2x easily

2) glibc may call unmmap directly as an internal system call by using system call number. so DFSan has no way to release shadow spaces for those unmmap.

Using sanitizer allocator addresses the above issues
1) its memory management is close to tcmalloc

2) we can register callback when sanitizer allocator calls unmmap, so dfsan can release shadow spaces correctly.

Our experiment with internal server-based application proved that with the change, in a-few-day run, memory usage leakage is close to what tcmalloc does w/o dfsan.

This change mainly follows MSan's code.

1) define allocator callbacks at dfsan_allocator.h|cpp

2) mark allocator APIs to be discard

3) intercept allocator APIs

4) make dfsan_set_label consistent with MSan's SetShadow when setting 0 labels, define dfsan_release_meta_memory when unmap is called

5) add flags about whether zeroing memory after malloc/free. dfsan works at byte-level, so bit-level oparations can cause reading undefined shadow. See D96842. zeroing memory after malloc helps this. About zeroing after free, reading after free is definitely UB, but if user code does so, it is hard to debug an overtainting caused by this w/o running MSan. So we add the flag to help debugging.

This change will be split to small changes for review. Before that, a question is
"this code shares a lot of with MSan, for example, dfsan_allocator.* and dfsan_new_delete.*.
Does it make sense to unify the code at sanitizer_common? will that introduce some
maintenance issue?"

Reviewed By: morehouse

Differential Revision: https://reviews.llvm.org/D101204