On ARM machine, $a/$d symbols are used by the compiler to mark the beginning of code/data part in code section. These symbols are filtered out when linking vmlinux(see scripts/kallsyms.c ignored_prefixes), but are left on modules. So there are $a symbols in /proc/kallsyms whose address overlap with the actual module symbols and can confuse tools such as perf when resolving kernel symbols. A sample stacktrace shown by perf script: c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms]) bf4a66d8 $a+0x78 ([test_module]) // $a is shown instead of actual sym name c0a4f5f4 kthread+0x15c ([kernel.kallsyms]) c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms]) This patch set contains 2 patches to fix such problem: The 1st patch modifies perf userspace tools to ignore $a/$d symbols from /proc/kallsyms. So people can use new perf tool to get correct kernel symbol on arm machines instead of updating kernel image. The 2nd patch modifies the logic of loading modules to ignore arm mapping symbols in the first place. Being left out in vmlinux and kernelspace API (e.g. module_kallsyms_on_each_symbol) means these symbols are not used anywhere, so it should be safe to remove them from module kallsyms list. v2: - Add 2nd patch as discussed with James Clark, see: https://lore.kernel.org/all/c7dfbd17-85fd-b914-b90f-082abc64c9d1@xxxxxxx/ Lexi Shao (2): perf symbol: ignore $a/$d symbols for ARM modules kallsyms: ignore arm mapping symbols when loading module kernel/module.c | 19 +++++++++++-------- tools/perf/util/symbol.c | 4 ++++ 2 files changed, 15 insertions(+), 8 deletions(-) -- 2.12.3
