Re: [PATCH v4] perf record: collect user registers set jointly with dwarf stacks
From: Arnaldo Carvalho de Melo
Date: Wed May 29 2019 - 15:28:44 EST
Em Wed, May 29, 2019 at 05:30:49PM +0300, Alexey Budankov escreveu:
>
> When dwarf stacks are collected jointly with user specified register
> set using --user-regs option like below the full register context is
> still 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_regs)
> are collected anyways regardless of the --user-regs option value provided
> from the command line:
>
> -g call-graph dwarf,K full_regs
> -g call-graph dwarf,K --user-regs=user_regs user_regs + dwarf_regs
> --user-regs=user_regs user_regs
>
> $ perf record -g --call-graph dwarf,1024 --user-regs=BP -- ls
> WARNING: specified --user-regs register set doesn't include registers needed by also specified --call-graph=dwarf, auto adding IP, SP registers.
> 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.budankov@xxxxxxxxxxxxxxx>
> ---
> 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..426dfefeecda 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -669,6 +669,9 @@ int perf_evsel__group_desc(struct perf_evsel *evsel, char *buf, size_t size)
> return ret;
> }
>
> +#define DWARF_REGS_MASK ((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 +705,13 @@ 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) {
Where are you checking that opts->sample_user_regs doesn't have either
IP or SP?
So, __perf_evsel__config_callchain its the routine that sets up the
attr->sample_regs_user when callchains are asked for, and what was it
doing? Asking for _all_ user regs, right?
I.e. what you're saying is that when --callgraph-dwarf is asked for,
then only IP and BP are needed, and we should stop doing that, so that
would be a first patch, if that is the case. I.e. a patch that doesn't
even mention opts->sample_user_regs.
Then, a second patch would fix the opt->sample_user_regs request clash
with --callgraph dwarf, i.e. it would do something like:
if ((opts->sample_regs_user & DWARF_REGS_MASK) != DWARF_REGS_MASK) {
char * ip = (opts->sample_regs_user & (1ULL << PERF_REG_IP)) ? NULL : "IP",
* sp = (opts->sample_regs_user & (1ULL << PERF_REG_SP)) ? NULL : "SP",
* all = (!ip && !sp) ? "s" : "";
pr_warning("WARNING: specified --user-regs register set doesn't include register%s "
"needed by also specified --call-graph=dwarf, auto adding %s%s%s register%s.\n",
all, ip, all : ", " : "", sp, all);
}
This if and only if all the registers that are needed to do DWARF
unwinding are just IP and BP, which doesn't look like its true, since
when no --user_regs is set (i.e. opts->user_regs is not set) then we
continue asking for PERF_REGS_MASK...
Can you check where I'm missing something?
Jiri DWARF unwind uses just IP and SP? Looking at
tools/perf/util/unwind-libunwind-local.c's access_reg() I don't think
so, right?
- Arnaldo
> + attr->sample_regs_user |= DWARF_REGS_MASK;
> + pr_warning("WARNING: specified --user-regs register set doesn't include registers "
> + "needed by also specified --call-graph=dwarf, auto adding IP, SP registers.\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
--
- Arnaldo