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Subject[PATCH 06/85] perf record: Allow mixing --user-regs with --call-graph=dwarf
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From: Alexey Budankov <alexey.budankov@linux.intel.com>

When DWARF stacks were requested and at the same time that the user
specifies a register set using the --user-regs option the full register
context was being captured on samples:

$ 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

I.e. the --user-regs=IP,SP,BP was being ignored, being overridden by the
needs of --call-graph=dwarf.

After applying the change in this patch the sample data contains the
user specified register, but making sure that at least the minimal set
of register needed for DWARF unwinding (DWARF_MINIMAL_REGS) is
requested.

The user is warned that DWARF unwinding may not work if extra registers
end up being needed.

-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

Committer notes:

Detected build failures on arches where PERF_REGS_ is not available,
such as debian:experimental-x-{mips,mips64,mipsel}, fedora 24 and 30 for
ARC uClibc and glibc, reported to Alexey that provided a patch moving
the DWARF_MINIMAL_REGS from evsel.c to util/perf_regs.h, where it is
guarded by an HAVE_PERF_REGS_SUPPORT ifdef.

Committer testing:

# perf record --user-regs=bp,ax -a sleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 1.955 MB perf.data (1773 samples) ]
# perf script -F+uregs | grep AX: | head -5
perf 1719 [000] 181.272398: 1 cycles: ffffffffba06a7c4 native_write_msr+0x4 (/lib/modules/5.2.0-rc1+/build/vmlinux) ABI:2 AX:0xffffffffffffffda BP:0x7ffef828fb00
perf 1719 [000] 181.272402: 1 cycles: ffffffffba06a7c4 native_write_msr+0x4 (/lib/modules/5.2.0-rc1+/build/vmlinux) ABI:2 AX:0xffffffffffffffda BP:0x7ffef828fb00
perf 1719 [000] 181.272403: 8 cycles: ffffffffba06a7c4 native_write_msr+0x4 (/lib/modules/5.2.0-rc1+/build/vmlinux) ABI:2 AX:0xffffffffffffffda BP:0x7ffef828fb00
perf 1719 [000] 181.272405: 181 cycles: ffffffffba06a7c6 native_write_msr+0x6 (/lib/modules/5.2.0-rc1+/build/vmlinux) ABI:2 AX:0xffffffffffffffda BP:0x7ffef828fb00
perf 1719 [000] 181.272406: 4405 cycles: ffffffffba06a7c4 native_write_msr+0x4 (/lib/modules/5.2.0-rc1+/build/vmlinux) ABI:2 AX:0xffffffffffffffda BP:0x7ffef828fb00
# perf record --call-graph=dwarf --user-regs=bp,ax -a sleep 1
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.
[ perf record: Woken up 55 times to write data ]
[ perf record: Captured and wrote 24.184 MB perf.data (2841 samples) ]
[root@quaco ~]# perf script --hide-call-graph -F+uregs | grep AX: | head -5
perf 1729 [000] 211.268006: 1 cycles: ffffffffba06a7c4 native_write_msr+0x4 (/lib/modules/5.2.0-rc1+/build/vmlinux) ABI:2 AX:0xffffffffffffffda BP:0x7ffc8679abb0 SP:0x7ffc8679ab78 IP:0x7fa75223a0db
perf 1729 [000] 211.268014: 1 cycles: ffffffffba06a7c4 native_write_msr+0x4 (/lib/modules/5.2.0-rc1+/build/vmlinux) ABI:2 AX:0xffffffffffffffda BP:0x7ffc8679abb0 SP:0x7ffc8679ab78 IP:0x7fa75223a0db
perf 1729 [000] 211.268017: 5 cycles: ffffffffba06a7c4 native_write_msr+0x4 (/lib/modules/5.2.0-rc1+/build/vmlinux) ABI:2 AX:0xffffffffffffffda BP:0x7ffc8679abb0 SP:0x7ffc8679ab78 IP:0x7fa75223a0db
perf 1729 [000] 211.268020: 48 cycles: ffffffffba06a7c6 native_write_msr+0x6 (/lib/modules/5.2.0-rc1+/build/vmlinux) ABI:2 AX:0xffffffffffffffda BP:0x7ffc8679abb0 SP:0x7ffc8679ab78 IP:0x7fa75223a0db
perf 1729 [000] 211.268024: 490 cycles: ffffffffba00e471 intel_bts_enable_local+0x21 (/lib/modules/5.2.0-rc1+/build/vmlinux) ABI:2 AX:0xffffffffffffffda BP:0x7ffc8679abb0 SP:0x7ffc8679ab78 IP:0x7fa75223a0db
#

Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/e7fd37b1-af22-0d94-a0dc-5895e803bbfe@linux.intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/util/evsel.c | 9 ++++++++-
tools/perf/util/perf_regs.h | 4 ++++
2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index a6f572a40deb..cc6e7a0dda92 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -702,7 +702,14 @@ 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 && DWARF_MINIMAL_REGS != PERF_REGS_MASK) {
+ 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 {
diff --git a/tools/perf/util/perf_regs.h b/tools/perf/util/perf_regs.h
index cb9c246c8962..47fe34e5f7d5 100644
--- a/tools/perf/util/perf_regs.h
+++ b/tools/perf/util/perf_regs.h
@@ -29,12 +29,16 @@ uint64_t arch__user_reg_mask(void);
#ifdef HAVE_PERF_REGS_SUPPORT
#include <perf_regs.h>

+#define DWARF_MINIMAL_REGS ((1ULL << PERF_REG_IP) | (1ULL << PERF_REG_SP))
+
int perf_reg_value(u64 *valp, struct regs_dump *regs, int id);

#else
#define PERF_REGS_MASK 0
#define PERF_REGS_MAX 0

+#define DWARF_MINIMAL_REGS PERF_REGS_MASK
+
static inline const char *perf_reg_name(int id __maybe_unused)
{
return NULL;
--
2.20.1
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