When dwarf stacks are collected jointly with user specified register
set using --user-regs option like below the full register context is
captured on a sample:
$ perf record -g --call-graph dwarf,1024 --user-regs=IP,SP,BP --
stack_test2.g.O3
188143843893585 0x6b48 [0x4f8]: PERF_RECORD_SAMPLE(IP, 0x4002): 23828/23828:
0x401236 period: 1363819 addr: 0x7ffedbdd51ac
... FP chain: nr:0
... user regs: mask 0xff0fff ABI 64-bit
.... AX 0x53b
.... BX 0x7ffedbdd3cc0
.... CX 0xffffffff
.... DX 0x33d3a
.... SI 0x7f09b74c38d0
.... DI 0x0
.... BP 0x401260
.... SP 0x7ffedbdd3cc0
.... IP 0x401236
.... FLAGS 0x20a
.... CS 0x33
.... SS 0x2b
.... R8 0x7f09b74c3800
.... R9 0x7f09b74c2da0
.... R10 0xfffffffffffff3ce
.... R11 0x246
.... R12 0x401070
.... R13 0x7ffedbdd5db0
.... R14 0x0
.... R15 0x0
... ustack: size 1024, offset 0xe0
. data_src: 0x5080021
... thread: stack_test2.g.O:23828
...... dso: /root/abudanko/stacks/stack_test2.g.O3
After applying the change suggested in the patch the sample data contain
only user specified register values. IP and SP registers (DWARF_MINIMAL_REGS)
are collected anyways regardless of the --user-regs value provided from
the command line:
-g call-graph dwarf,K full_regs
--user-regs=user_regs user_regs
-g call-graph dwarf,K --user-regs=user_regs user_regs + DWARF_MINIMAL_REGS
$ perf record -g --call-graph dwarf,1024 --user-regs=BP -- ls
WARNING: The use of --call-graph=dwarf may require all the user registers,
specifying a subset with --user-regs may render DWARF unwinding unreliable, so
the minimal registers set (IP, SP) is explicitly forced.
arch COPYING Documentation include Kbuild lbuild MAINTAINERS
modules.builtin Module.symvers perf.data.old scripts System.map
virt
block CREDITS drivers init Kconfig lib Makefile
modules.builtin.modinfo net README security tools
vmlinux
certs crypto fs ipc kernel LICENSES mm
modules.order perf.data samples sound usr
vmlinux.o
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.030 MB perf.data (10 samples) ]
188368474305373 0x5e40 [0x470]: PERF_RECORD_SAMPLE(IP, 0x4002): 23839/23839:
0x401236 period: 1260507 addr: 0x7ffd3d85e96c
... FP chain: nr:0
... user regs: mask 0x1c0 ABI 64-bit
.... BP 0x401260
.... SP 0x7ffd3d85cc20
.... IP 0x401236
... ustack: size 1024, offset 0x58
. data_src: 0x5080021
Signed-off-by: Alexey Budankov <alexey.budan...@linux.intel.com>
---
Changes in v5:
- renamed minimal dwarf regs set macro to DWARF_MINIMAL_REGS
- edited warning message
Changes in v4:
- added warning message about dwarf registers unconditionally
included into the collected registers set
Changes in v3:
- avoid changes in platform specific header files
Changes in v2:
- implemented dwarf register set to avoid corrupted trace
when --user-regs option value omits IP,SP
---
tools/perf/util/evsel.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index a6f572a40deb..375ab4eb7560 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -669,6 +669,8 @@ int perf_evsel__group_desc(struct perf_evsel *evsel, char
*buf, size_t size)
return ret;
}
+#define DWARF_MINIMAL_REGS ((1ULL << PERF_REG_IP) | (1ULL << PERF_REG_SP))
+
static void __perf_evsel__config_callchain(struct perf_evsel *evsel,
struct record_opts *opts,
struct callchain_param *param)
@@ -702,7 +704,14 @@ static void __perf_evsel__config_callchain(struct
perf_evsel *evsel,
if (!function) {
perf_evsel__set_sample_bit(evsel, REGS_USER);
perf_evsel__set_sample_bit(evsel, STACK_USER);
- attr->sample_regs_user |= PERF_REGS_MASK;
+ if (opts->sample_user_regs) {
+ attr->sample_regs_user |= DWARF_MINIMAL_REGS;
+ pr_warning("WARNING: The use of
--call-graph=dwarf may require all the user registers, "
+ "specifying a subset with
--user-regs may render DWARF unwinding unreliable, "
+ "so the minimal registers set (IP,
SP) is explicitly forced.\n");
+ } else {
+ attr->sample_regs_user |= PERF_REGS_MASK;
+ }
attr->sample_stack_user = param->dump_size;
attr->exclude_callchain_user = 1;
} else {
--
2.20.1
