4.19-stable review patch. If anyone has any objections, please let me know.
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From: Leo Yan leo.yan@arm.com
[ Upstream commit 314909f13cc12d47c468602c37dace512d225eeb ]
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 leo.yan@arm.com Acked-by: Masami Hiramatsu (Google) mhiramat@kernel.org Link: https://lore.kernel.org/r/20241012141432.877894-1-leo.yan@arm.com Signed-off-by: Namhyung Kim namhyung@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- tools/perf/util/probe-finder.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-)
diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c index 4da4ec2552463..38b8a657196d9 100644 --- a/tools/perf/util/probe-finder.c +++ b/tools/perf/util/probe-finder.c @@ -1593,8 +1593,21 @@ int debuginfo__find_probe_point(struct debuginfo *dbg, unsigned long addr,
/* Find a corresponding function (name, baseline and baseaddr) */ if (die_find_realfunc(&cudie, (Dwarf_Addr)addr, &spdie)) { - /* Get function entry information */ - func = basefunc = dwarf_diename(&spdie); + /* + * Get function entry information. + * + * As described in the document DWARF Debugging Information + * Format Version 5, section 2.22 Linkage Names, "mangled names, + * are used in various ways, ... to distinguish multiple + * entities that have the same name". + * + * Firstly try to get distinct linkage name, if fail then + * rollback to get associated name in DIE. + */ + func = basefunc = die_get_linkage_name(&spdie); + if (!func) + func = basefunc = dwarf_diename(&spdie); + if (!func || die_entrypc(&spdie, &baseaddr) != 0 || dwarf_decl_line(&spdie, &baseline) != 0) {