perf symbols: Ignore $a/$d symbols for ARM modules

On anARM machine, kernel symbols from modules can be resolved to $a
instead of printing the actual symbol name. Ignore symbols starting with
"$" when building kallsyms rbtree.

A sample stacktrace is shown as follows:

  c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms])
  bf4a66d8 $a+0x78 ([test_module])
  c0a4f5f4 kthread+0x15c ([kernel.kallsyms])
  c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms])

On an 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 which
share the same addresses with the actual module symbols and confuses
perf when resolving symbols.

After this patch, the module symbol name is printed:

  c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms])
  bf4a66d8 test_func+0x78 ([test_module])
  c0a4f5f4 kthread+0x15c ([kernel.kallsyms])
  c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms])

Reviewed-by: James Clark <[email protected]>
Signed-off-by: Lexi Shao <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Andrii Nakryiko <[email protected]>
Cc: Daniel Borkmann <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jessica Yu <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: John Fastabend <[email protected]>
Cc: KP Singh <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Martin KaFai Lau <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Nathan Chancellor <[email protected]>
Cc: Nick Desaulniers <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: QiuXi <[email protected]>
Cc: Song Liu <[email protected]>
Cc: Wangbing <[email protected]>
Cc: Xiaoming Ni <[email protected]>
Cc: Yonghong Song <[email protected]>
Cc: [email protected]
Cc: [email protected]
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

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