When using GCC on x86-64 to compile an usdt prog with -O1 or higher optimization, the compiler will generate SIB addressing mode for global array and PC-relative addressing mode for global variable, e.g. "1@-96(%rbp,%rax,8)" and "-1@4+t1(%rip)".
The current USDT implementation in libbpf cannot parse these two formats, causing `bpf_program__attach_usdt()` to fail with -ENOENT (unrecognized register).
This patch series adds support for SIB addressing mode in USDT probes. The main changes include: - add correct handling logic for SIB-addressed arguments in `parse_usdt_arg`. - add an usdt_o2 test case to cover SIB addressing mode.
Testing shows that the SIB probe correctly generates 8@(%rcx,%rax,8) argument spec and passes all validation checks.
The modification history of this patch series: Change since v1: - refactor the code to make it more readable - modify the commit message to explain why and how
Change since v2: - fix the `scale` uninitialized error
Change since v3: - force -O2 optimization for usdt.test.o to generate SIB addressing usdt and pass all test cases.
Change since v4: - split the patch into two parts, one for the fix and the other for the test
Change since v5: - Only enable optimization for x86 architecture to generate SIB addressing usdt argument spec.
Change since v6: - Add an usdt_o2 test case to cover SIB addressing mode. - Reinstate the usdt.c test case.
Change since v7: - Refactor modifications to __bpf_usdt_arg_spec to avoid increasing its size, achieving better compatibility - Fix some minor code style issues - Refactor the usdt_o2 test case, removing semaphore and adding GCC attribute to force -O2 optimization
Change since v8: - Refactor the usdt_o2 test case, using assembly to force SIB addressing mode.
Change since v9: - Only enable the usdt_o2 test case on x86_64 and i386 architectures since the SIB addressing mode is only supported on x86_64 and i386.
Jiawei Zhao (3): libbpf: fix USDT SIB argument handling causing unrecognized register error selftests/bpf: Add an usdt_o2 test case in selftests to cover SIB handling logic selftests/bpf: make usdt_o2 reliably generate SIB USDT arg spec
tools/lib/bpf/usdt.bpf.h | 54 ++++++++++++- tools/lib/bpf/usdt.c | 61 ++++++++++++-- tools/testing/selftests/bpf/Makefile | 1 + .../selftests/bpf/prog_tests/usdt_o2.c | 79 +++++++++++++++++++ .../selftests/bpf/progs/test_usdt_o2.c | 37 +++++++++ 5 files changed, 225 insertions(+), 7 deletions(-) create mode 100644 tools/testing/selftests/bpf/prog_tests/usdt_o2.c create mode 100644 tools/testing/selftests/bpf/progs/test_usdt_o2.c