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 v2:
- Add uretprobe selfttest (Alan)
- Check symbol exact match (Alan)
- Fix typo (Jiri)
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/CAEf4BzZTrjjyyOm3ak9JsssPSh6T_ZmGd677a2rt5e5rBLUrpQ@xxxxxxxxxxxxxx/
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
