[PATCH] perf: disable kernel symbol demangling by default

From: Avi Kivity
Date: Sat Sep 13 2014 - 00:15:16 EST

Some Linux symbols (for example __vt_event_wait) are interpreted by
the demangler as C++ mangled names, which of course they aren't.

Disable kernel symbol demangling by default to avoid this, and
allow enabling it with a new option --demangle-kernel for those who
wish it.

Reported-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Signed-off-by: Avi Kivity <avi@xxxxxxxxxxxxxxxxxxxx>
---
tools/perf/Documentation/perf-probe.txt | 3 +++
tools/perf/Documentation/perf-report.txt | 3 +++
tools/perf/Documentation/perf-top.txt | 3 +++
tools/perf/builtin-probe.c | 2 ++
tools/perf/builtin-report.c | 2 ++
tools/perf/builtin-top.c | 2 ++
tools/perf/util/symbol-elf.c | 9 ++++++++-
tools/perf/util/symbol.c | 1 +
tools/perf/util/symbol.h | 1 +
9 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/tools/perf/Documentation/perf-probe.txt b/tools/perf/Documentation/perf-probe.txt
index 1513935..aaa869b 100644
--- a/tools/perf/Documentation/perf-probe.txt
+++ b/tools/perf/Documentation/perf-probe.txt
@@ -104,6 +104,9 @@ OPTIONS
Specify path to the executable or shared library file for user
space tracing. Can also be used with --funcs option.

+--demangle-kernel::
+ Demangle kernel symbols.
+
In absence of -m/-x options, perf probe checks if the first argument after
the options is an absolute path name. If its an absolute path, perf probe
uses it as a target module/target user space binary to probe.
diff --git a/tools/perf/Documentation/perf-report.txt b/tools/perf/Documentation/perf-report.txt
index d2b59af..cccb160 100644
--- a/tools/perf/Documentation/perf-report.txt
+++ b/tools/perf/Documentation/perf-report.txt
@@ -276,6 +276,9 @@ OPTIONS
Demangle symbol names to human readable form. It's enabled by default,
disable with --no-demangle.

+--demangle-kernel::
+ Demangle kernel symbol names to human readable form (for C++ kernels).
+
--mem-mode::
Use the data addresses of samples in addition to instruction addresses
to build the histograms. To generate meaningful output, the perf.data
diff --git a/tools/perf/Documentation/perf-top.txt b/tools/perf/Documentation/perf-top.txt
index 180ae02..f1f728a 100644
--- a/tools/perf/Documentation/perf-top.txt
+++ b/tools/perf/Documentation/perf-top.txt
@@ -98,6 +98,9 @@ Default is to monitor all CPUS.
--hide_user_symbols::
Hide user symbols.

+--demangle-kernel::
+ Demangle kernel symbols.
+
-D::
--dump-symtab::
Dump the symbol table used for profiling.
diff --git a/tools/perf/builtin-probe.c b/tools/perf/builtin-probe.c
index c63fa29..41ee517 100644
--- a/tools/perf/builtin-probe.c
+++ b/tools/perf/builtin-probe.c
@@ -373,6 +373,8 @@ __cmd_probe(int argc, const char **argv, const char *prefix __maybe_unused)
"target executable name or path", opt_set_target),
OPT_BOOLEAN(0, "demangle", &symbol_conf.demangle,
"Disable symbol demangling"),
+ OPT_BOOLEAN(0, "demangle-kernel", &symbol_conf.demangle_kernel,
+ "Enable kernel symbol demangling"),
OPT_END()
};
int ret;
diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
index 21d830b..9b39822 100644
--- a/tools/perf/builtin-report.c
+++ b/tools/perf/builtin-report.c
@@ -674,6 +674,8 @@ int cmd_report(int argc, const char **argv, const char *prefix __maybe_unused)
"objdump binary to use for disassembly and annotations"),
OPT_BOOLEAN(0, "demangle", &symbol_conf.demangle,
"Disable symbol demangling"),
+ OPT_BOOLEAN(0, "demangle-kernel", &symbol_conf.demangle_kernel,
+ "Enable kernel symbol demangling"),
OPT_BOOLEAN(0, "mem-mode", &report.mem_mode, "mem access profile"),
OPT_CALLBACK(0, "percent-limit", &report, "percent",
"Don't show entries under that percent", parse_percent_limit),
diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index 377971d..470bf24 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -1122,6 +1122,8 @@ int cmd_top(int argc, const char **argv, const char *prefix __maybe_unused)
"Interleave source code with assembly code (default)"),
OPT_BOOLEAN(0, "asm-raw", &symbol_conf.annotate_asm_raw,
"Display raw encoding of assembly instructions (default)"),
+ OPT_BOOLEAN(0, "demangle-kernel", &symbol_conf.demangle_kernel,
+ "Enable kernel symbol demangling"),
OPT_STRING(0, "objdump", &objdump_path, "path",
"objdump binary to use for disassembly and annotations"),
OPT_STRING('M', "disassembler-style", &disassembler_style, "disassembler style",
diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index d753499..a9af919 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -680,6 +680,13 @@ static u64 ref_reloc(struct kmap *kmap)
return 0;
}

+static bool want_demangle(bool is_kernel_sym)
+{
+ return is_kernel_sym
+ ? symbol_conf.demangle_kernel
+ : symbol_conf.demangle;
+}
+
int dso__load_sym(struct dso *dso, struct map *map,
struct symsrc *syms_ss, struct symsrc *runtime_ss,
symbol_filter_t filter, int kmodule)
@@ -938,7 +945,7 @@ new_symbol:
* DWARF DW_compile_unit has this, but we don't always have access
* to it...
*/
- if (symbol_conf.demangle) {
+ if (want_demangle(dso->kernel || kmodule)) {
demangled = bfd_demangle(NULL, elf_name,
DMGL_PARAMS | DMGL_ANSI);
if (demangled != NULL)
diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index eb06746..e2ab1da 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -33,6 +33,7 @@ struct symbol_conf symbol_conf = {
.try_vmlinux_path = true,
.annotate_src = true,
.demangle = true,
+ .demangle_kernel = false,
.cumulate_callchain = true,
.show_hist_headers = true,
.symfs = "",
diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
index e7295e9..4616705 100644
--- a/tools/perf/util/symbol.h
+++ b/tools/perf/util/symbol.h
@@ -118,6 +118,7 @@ struct symbol_conf {
annotate_src,
event_group,
demangle,
+ demangle_kernel,
filter_relative,
show_hist_headers;
const char *vmlinux_name,
--
1.9.3

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