On 9/14/21 6:55 PM, Alexei Starovoitov wrote:
On Tue, Sep 14, 2021 at 3:30 PM Yonghong Song <yhs@xxxxxx> wrote:LLVM14 added support for a new C attribute ([1]) __attribute__((btf_tag("arbitrary_str"))) This attribute will be emitted to dwarf ([2]) and pahole will convert it to BTF. Or for bpf target, this attribute will be emitted to BTF directly ([3], [4]). The attribute is intended to provide additional information for - struct/union type or struct/union member - static/global variables - static/global function or function parameter. This new attribute can be used to add attributes to kernel codes, e.g., pre- or post- conditions, allow/deny info, or any other info in which only the kernel is interested. Such attributes will be processed by clang frontend and emitted to dwarf, converting to BTF by pahole. Ultimiately the verifier can use these information for verification purpose. The new attribute can also be used for bpf programs, e.g., tagging with __user attributes for function parameters, specifying global function preconditions, etc. Such information may help verifier to detect user program bugs. After this series, pahole dwarf->btf converter will be enhanced to support new llvm tag for btf_tag attribute. With pahole support, we will then try to add a few real use case, e.g., __user/__rcu tagging, allow/deny list, some kernel function precondition, etc, in the kernel. In the rest of the series, Patches 1-2 had kernel support. Patches 3-4 added libbpf support. Patch 5 added bpftool support. Patches 6-10 added various selftests. Patch 11 added documentation for the new kind. [1] https://reviews.llvm.org/D106614 [2] https://reviews.llvm.org/D106621 [3] https://reviews.llvm.org/D106622 [4] https://reviews.llvm.org/D109560 Changelog: v2 -> v3: - put NR_BTF_KINDS and BTF_KIND_MAX into enum as well - check component_idx earlier (check_meta stage) in kernel - add more tests - fix misc nitsApplied. Please send an update to selftests/bpf/README. Since folks will be puzzled with messages: progs/tag.c:23:20: warning: unknown attribute 'btf_tag' ignored [-Wunknown-attributes]
Ya, this is not good. I too focused on the latest clang which has btf_tag support.
Even with old clang: ./test_progs -t tag #21 btf_tag:OK Summary: 1/0 PASSED, 0 SKIPPED, 0 FAILED The test probably should fail with old clang ?
I will follow atomics example, if btf_tag is not supported, the test will be marked as SKIP. Will also update selftests/bpf/README for when SKIP message may appear. Will send the followup patch soon.
