From: Andrii Nakryiko Date: Mon, 4 Apr 2022 00:55:46 +0000 (-0700) Subject: Merge branch 'libbpf: name-based u[ret]probe attach' X-Git-Tag: v5.19~462^2~363^2~31 X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=88d01a57113a361c1e62abaeed0563745d637888;p=mirror_ubuntu-kernels.git Merge branch 'libbpf: name-based u[ret]probe attach' Alan Maguire says: ==================== This patch series focuses on supporting name-based attach - similar to that supported for kprobes - for uprobe BPF programs. Currently attach for such probes is done by determining the offset manually, so the aim is to try and mimic the simplicity of kprobe attach, making use of uprobe opts to specify a name string. Patch 1 supports expansion of the binary_path argument used for bpf_program__attach_uprobe_opts(), allowing it to determine paths for programs and shared objects automatically, allowing for specification of "libc.so.6" rather than the full path "/usr/lib64/libc.so.6". Patch 2 adds the "func_name" option to allow uprobe attach by name; the mechanics are described there. Having name-based support allows us to support auto-attach for uprobes; patch 3 adds auto-attach support while attempting to handle backwards-compatibility issues that arise. The format supported is u[ret]probe/binary_path:[raw_offset|function[+offset]] For example, to attach to libc malloc: SEC("uprobe//usr/lib64/libc.so.6:malloc") ..or, making use of the path computation mechanisms introduced in patch 1 SEC("uprobe/libc.so.6:malloc") Finally patch 4 add tests to the attach_probe selftests covering attach by name, with patch 5 covering skeleton auto-attach. Changes since v4 [1]: - replaced strtok_r() usage with copying segments from static char *; avoids unneeded string allocation (Andrii, patch 1) - switched to using access() instead of stat() when checking path-resolved binary (Andrii, patch 1) - removed computation of .plt offset for instrumenting shared library calls within binaries. Firstly it proved too brittle, and secondly it was somewhat unintuitive in that this form of instrumentation did not support function+offset as the "local function in binary" and "shared library function in shared library" cases did. We can still instrument library calls, just need to do it in the library .so (patch 2) - added binary path logging in cases where it was missing (Andrii, patch 2) - avoid strlen() calcuation in checking name match (Andrii, patch 2) - reword comments for func_name option (Andrii, patch 2) - tightened SEC() name validation to support "u[ret]probe" and fail on other permutations that do not support auto-attach (i.e. have u[ret]probe/binary_path:func format (Andrii, patch 3) - fixed selftests to fail independently rather than skip remainder on failure (Andrii, patches 4,5) Changes since v3 [2]: - reworked variable naming to fit better with libbpf conventions (Andrii, patch 2) - use quoted binary path in log messages (Andrii, patch 2) - added path determination mechanisms using LD_LIBRARY_PATH/PATH and standard locations (patch 1, Andrii) - changed section lookup to be type+name (if name is specified) to simplify use cases (patch 2, Andrii) - fixed .plt lookup scheme to match symbol table entries with .plt index via the .rela.plt table; also fix the incorrect assumption that the code in the .plt that does library linking is the same size as .plt entries (it just happens to be on x86_64) - aligned with pluggable section support such that uprobe SEC() names that do not conform to auto-attach format do not cause skeleton load failure (patch 3, Andrii) - no longer need to look up absolute path to libraries used by test_progs since we have mechanism to determine path automatically - replaced CHECK()s with ASSERT*()s for attach_probe test (Andrii, patch 4) - added auto-attach selftests also (Andrii, patch 5) Changes since RFC [3]: - used "long" for addresses instead of ssize_t (Andrii, patch 1). - used gelf_ interfaces to avoid assumptions about 64-bit binaries (Andrii, patch 1) - clarified string matching in symbol table lookups (Andrii, patch 1) - added support for specification of shared object functions in a non-shared object binary. This approach instruments the Procedure Linking Table (PLT) - malloc@PLT. - changed logic in symbol search to check dynamic symbol table first, then fall back to symbol table (Andrii, patch 1). - modified auto-attach string to require "/" separator prior to path prefix i.e. uprobe//path/to/binary (Andrii, patch 2) - modified auto-attach string to use ':' separator (Andrii, patch 2) - modified auto-attach to support raw offset (Andrii, patch 2) - modified skeleton attach to interpret -ESRCH errors as a non-fatal "unable to auto-attach" (Andrii suggested -EOPNOTSUPP but my concern was it might collide with other instances where that value is returned and reflects a failure to attach a to-be-expected attachment rather than skip a program that does not present an auto-attachable section name. Admittedly -EOPNOTSUPP seems a more natural value here). - moved library path retrieval code to trace_helpers (Andrii, patch 3) [1] https://lore.kernel.org/bpf/1647000658-16149-1-git-send-email-alan.maguire@oracle.com/ [2] https://lore.kernel.org/bpf/1643645554-28723-1-git-send-email-alan.maguire@oracle.com/ [3] https://lore.kernel.org/bpf/1642678950-19584-1-git-send-email-alan.maguire@oracle.com/ ==================== Signed-off-by: Andrii Nakryiko --- 88d01a57113a361c1e62abaeed0563745d637888