[bpf-next,v2,0/3] libbpf: Support symbol versioning for uprobe

Message

Hengqi Chen Sept. 5, 2023, 3:12 p.m. UTC

Dynamic symbols in shared library may have the same name, for example:

    $ nm -D /lib/x86_64-linux-gnu/libc.so.6 | grep rwlock_wrlock
    000000000009b1a0 T __pthread_rwlock_wrlock@GLIBC_2.2.5
    000000000009b1a0 T pthread_rwlock_wrlock@@GLIBC_2.34
    000000000009b1a0 T pthread_rwlock_wrlock@GLIBC_2.2.5

    $ readelf -W --dyn-syms /lib/x86_64-linux-gnu/libc.so.6 | grep rwlock_wrlock
      706: 000000000009b1a0   878 FUNC    GLOBAL DEFAULT   15 __pthread_rwlock_wrlock@GLIBC_2.2.5
      2568: 000000000009b1a0   878 FUNC    GLOBAL DEFAULT   15 pthread_rwlock_wrlock@@GLIBC_2.34
      2571: 000000000009b1a0   878 FUNC    GLOBAL DEFAULT   15 pthread_rwlock_wrlock@GLIBC_2.2.5

There are two pthread_rwlock_wrlock symbols in libc.so .dynsym section.
The one with @@ is the default version, the other is hidden.
Note that the version info is stored in .gnu.version and .gnu.version_d
sections of libc and the two symbols are at the _same_ offset.

Currently, specify `pthread_rwlock_wrlock`, `pthread_rwlock_wrlock@@GLIBC_2.34`
or `pthread_rwlock_wrlock@GLIBC_2.2.5` in bpf_uprobe_opts::func_name won't work.
Because there are two `pthread_rwlock_wrlock` in .dynsym sections without the
version suffix and both are global bind.

We could solve this by introducing symbol versioning ([0]). So that users can
specify func, func@LIB_VERSION or func@@LIB_VERSION to attach a uprobe.

This patchset resolves symbol conflicts and add symbol versioning for uprobe.
  - Patch 1 resolves symbol conflicts at the same offset
  - Patch 2 adds symbol versioning for dynsym
  - Patch 3 adds selftests for the above changes

Changes from v1:
  - Address comments from Alan and Jiri
  - Add selftests (Someone reminds me that there is an attempt at [1]
    and part of the selftest code from Andrii is taken from there)

  [0]: https://refspecs.linuxfoundation.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/symversion.html
  [1]: https://lore.kernel.org/lkml/[e-mail]/

Hengqi Chen (3):
  libbpf: Resolve symbol conflicts at the same offset for uprobe
  libbpf: Support symbol versioning for uprobe
  selftests/bpf: Add tests for symbol versioning for uprobe

 tools/lib/bpf/elf.c                           | 150 ++++++++++++++++--
 tools/lib/bpf/libbpf.c                        |   2 +-
 tools/testing/selftests/bpf/Makefile          |   5 +-
 .../testing/selftests/bpf/liburandom_read.map |  15 ++
 .../testing/selftests/bpf/prog_tests/uprobe.c |  95 +++++++++++
 .../testing/selftests/bpf/progs/test_uprobe.c |  61 +++++++
 tools/testing/selftests/bpf/urandom_read.c    |   9 ++
 .../testing/selftests/bpf/urandom_read_lib1.c |  41 +++++
 8 files changed, 361 insertions(+), 17 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/liburandom_read.map
 create mode 100644 tools/testing/selftests/bpf/prog_tests/uprobe.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_uprobe.c

--
2.34.1