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When building the selftest with arm64/clang20, the following test failed: ... ubtest_multispec_usdt:PASS:usdt_100_called 0 nsec subtest_multispec_usdt:PASS:usdt_100_sum 0 nsec subtest_multispec_usdt:FAIL:usdt_300_bad_attach unexpected pointer: 0xaaaad82a2a80 #471/2 usdt/multispec:FAIL #471 usdt:FAIL But arm64/gcc11 built kernel selftests succeeded. Further debug found arm64/clang generated code has much less argument pattern after dedup, but gcc generated code has a lot more. Check usdt probes with usdt.test.o on arm64 platform: with gcc11 build binary: stapsdt 0x0000002e NT_STAPSDT (SystemTap probe descriptors) Provider: test Name: usdt_300 Location: 0x00000000000054f8, Base: 0x0000000000000000, Semaphore: 0x0000000000000008 Arguments: -4@[sp] stapsdt 0x00000031 NT_STAPSDT (SystemTap probe descriptors) Provider: test Name: usdt_300 Location: 0x0000000000005510, Base: 0x0000000000000000, Semaphore: 0x0000000000000008 Arguments: -4@[sp, 4] ... stapsdt 0x00000032 NT_STAPSDT (SystemTap probe descriptors) Provider: test Name: usdt_300 Location: 0x0000000000005660, Base: 0x0000000000000000, Semaphore: 0x0000000000000008 Arguments: -4@[sp, 60] ... stapsdt 0x00000034 NT_STAPSDT (SystemTap probe descriptors) Provider: test Name: usdt_300 Location: 0x00000000000070e8, Base: 0x0000000000000000, Semaphore: 0x0000000000000008 Arguments: -4@[sp, 1192] stapsdt 0x00000034 NT_STAPSDT (SystemTap probe descriptors) Provider: test Name: usdt_300 Location: 0x0000000000007100, Base: 0x0000000000000000, Semaphore: 0x0000000000000008 Arguments: -4@[sp, 1196] ... stapsdt 0x00000032 NT_STAPSDT (SystemTap probe descriptors) Provider: test Name: usdt_300 Location: 0x0000000000009ec4, Base: 0x0000000000000000, Semaphore: 0x0000000000000008 Arguments: -4@[sp, 60] with clang20 build binary: stapsdt 0x0000002e NT_STAPSDT (SystemTap probe descriptors) Provider: test Name: usdt_300 Location: 0x00000000000009a0, Base: 0x0000000000000000, Semaphore: 0x0000000000000008 Arguments: -4@[x9] stapsdt 0x0000002e NT_STAPSDT (SystemTap probe descriptors) Provider: test Name: usdt_300 Location: 0x00000000000009b8, Base: 0x0000000000000000, Semaphore: 0x0000000000000008 Arguments: -4@[x9] ... stapsdt 0x0000002e NT_STAPSDT (SystemTap probe descriptors) Provider: test Name: usdt_300 Location: 0x0000000000002590, Base: 0x0000000000000000, Semaphore: 0x0000000000000008 Arguments: -4@[x9] stapsdt 0x0000002e NT_STAPSDT (SystemTap probe descriptors) Provider: test Name: usdt_300 Location: 0x00000000000025a8, Base: 0x0000000000000000, Semaphore: 0x0000000000000008 Arguments: -4@[x8] ... stapsdt 0x0000002f NT_STAPSDT (SystemTap probe descriptors) Provider: test Name: usdt_300 Location: 0x0000000000007fdc, Base: 0x0000000000000000, Semaphore: 0x0000000000000008 Arguments: -4@[x10] There are total 300 locations for usdt_300. For gcc11 built binary, there are 300 spec's. But for clang20 built binary, there are 3 spec's. The default BPF_USDT_MAX_SPEC_CNT is 256, so bpf_program__attach_usdt() will fail for gcc but it will succeed with clang. To fix the problem, do not do bpf_program__attach_usdt() for usdt_300 with arm64/clang setup. Signed-off-by: Yonghong Song <yonghong.song@linux.dev> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20250624211802.2198821-1-yonghong.song@linux.dev
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.