perf probe: Correct demangled symbols in C++ program

An issue can be observed when probe C++ demangled symbol with steps:

  # nm test_cpp_mangle | grep print_data
    0000000000000c94 t _GLOBAL__sub_I__Z10print_datai
    0000000000000afc T _Z10print_datai
    0000000000000b38 T _Z10print_dataR5Point

  # perf probe -x /home/niayan01/test_cpp_mangle -F --demangle
    ...
    print_data(Point&)
    print_data(int)
    ...

  # perf --debug verbose=3 probe -x test_cpp_mangle --add "test=print_data(int)"
    probe-definition(0): test=print_data(int)
    symbol:print_data(int) file:(null) line:0 offset:0 return:0 lazy:(null)
    0 arguments
    Open Debuginfo file: /home/niayan01/test_cpp_mangle
    Try to find probe point from debuginfo.
    Symbol print_data(int) address found : afc
    Matched function: print_data [2ccf]
    Probe point found: print_data+0
    Found 1 probe_trace_events.
    Opening /sys/kernel/tracing//uprobe_events write=1
    Opening /sys/kernel/tracing//README write=0
    Writing event: p:probe_test_cpp_mangle/test /home/niayan01/test_cpp_mangle:0xb38
    ...

When tried to probe symbol "print_data(int)", the log shows:

    Symbol print_data(int) address found : afc

The found address is 0xafc - which is right with verifying the output
result from nm. Afterwards when write event, the command uses offset
0xb38 in the last log, which is a wrong address.

The dwarf_diename() gets a common function name, in above case, it
returns string "print_data". As a result, the tool parses the offset
based on the common name. This leads to probe at the wrong symbol
"print_data(Point&)".

To fix the issue, use the die_get_linkage_name() function to retrieve
the distinct linkage name - this is the mangled name for the C++ case.
Based on this unique name, the tool can get a correct offset for
probing. Based on DWARF doc, it is possible the linkage name is missed
in the DIE, it rolls back to use dwarf_diename().

After:

  # perf --debug verbose=3 probe -x test_cpp_mangle --add "test=print_data(int)"
    probe-definition(0): test=print_data(int)
    symbol:print_data(int) file:(null) line:0 offset:0 return:0 lazy:(null)
    0 arguments
    Open Debuginfo file: /home/niayan01/test_cpp_mangle
    Try to find probe point from debuginfo.
    Symbol print_data(int) address found : afc
    Matched function: print_data [2d06]
    Probe point found: print_data+0
    Found 1 probe_trace_events.
    Opening /sys/kernel/tracing//uprobe_events write=1
    Opening /sys/kernel/tracing//README write=0
    Writing event: p:probe_test_cpp_mangle/test /home/niayan01/test_cpp_mangle:0xafc
    Added new event:
      probe_test_cpp_mangle:test (on print_data(int) in /home/niayan01/test_cpp_mangle)

    You can now use it in all perf tools, such as:

            perf record -e probe_test_cpp_mangle:test -aR sleep 1

  # perf --debug verbose=3 probe -x test_cpp_mangle --add "test2=print_data(Point&)"
    probe-definition(0): test2=print_data(Point&)
    symbol:print_data(Point&) file:(null) line:0 offset:0 return:0 lazy:(null)
    0 arguments
    Open Debuginfo file: /home/niayan01/test_cpp_mangle
    Try to find probe point from debuginfo.
    Symbol print_data(Point&) address found : b38
    Matched function: print_data [2ccf]
    Probe point found: print_data+0
    Found 1 probe_trace_events.
    Opening /sys/kernel/tracing//uprobe_events write=1
    Parsing probe_events: p:probe_test_cpp_mangle/test /home/niayan01/test_cpp_mangle:0x0000000000000afc
    Group:probe_test_cpp_mangle Event:test probe:p
    Opening /sys/kernel/tracing//README write=0
    Writing event: p:probe_test_cpp_mangle/test2 /home/niayan01/test_cpp_mangle:0xb38
    Added new event:
      probe_test_cpp_mangle:test2 (on print_data(Point&) in /home/niayan01/test_cpp_mangle)

    You can now use it in all perf tools, such as:

            perf record -e probe_test_cpp_mangle:test2 -aR sleep 1

Fixes: fb1587d869a3 ("perf probe: List probes with line number and file name")
Signed-off-by: Leo Yan <[email protected]>
Acked-by: Masami Hiramatsu (Google) <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Namhyung Kim <[email protected]>

0 files changed, 0 insertions, 0 deletions