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In my locally build clang LTO kernel (enabling CONFIG_LTO and
CONFIG_LTO_CLANG_THIN), kprobe_multi_bench_attach/kernel subtest
failed like:
test_kprobe_multi_bench_attach:PASS:get_syms 0 nsec
test_kprobe_multi_bench_attach:PASS:kprobe_multi_empty__open_and_load 0 nsec
libbpf: prog 'test_kprobe_empty': failed to attach: No such process
test_kprobe_multi_bench_attach:FAIL:bpf_program__attach_kprobe_multi_opts unexpected error: -3
#117/1 kprobe_multi_bench_attach/kernel:FAIL
There are multiple symbols in /sys/kernel/debug/tracing/available_filter_functions
are renamed in /proc/kallsyms due to cross file inlining. One example is for
static function __access_remote_vm in mm/memory.c.
In a non-LTO kernel, we have the following call stack:
ptrace_access_vm (global, kernel/ptrace.c)
access_remote_vm (global, mm/memory.c)
__access_remote_vm (static, mm/memory.c)
With LTO kernel, it is possible that access_remote_vm() is inlined by
ptrace_access_vm(). So we end up with the following call stack:
ptrace_access_vm (global, kernel/ptrace.c)
__access_remote_vm (static, mm/memory.c)
The compiler renames __access_remote_vm to __access_remote_vm.llvm.<hash>
to prevent potential name collision.
The kernel bpf_kprobe_multi_link_attach() and ftrace_lookup_symbols() try
to find addresses based on /proc/kallsyms, hence the current test failed
with LTO kenrel.
This patch consulted /proc/kallsyms to find the corresponding entries
for the ksym and this solved the issue.
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20240326041518.1199758-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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.