[PATCH 17/23] perf script: Support -F brstackoff,dso

Arnaldo Carvalho de Melo
2017-06-20T02:00:07Z

From: Mark Santaniello <marksan@fb.com>

The idea here is to make AutoFDO easier in cloud environment with ASLR.
It's easiest to show how this is useful by example. I built a small test
akin to "while(1) { do_nothing(); }" where the do_nothing function is
loaded from a dso:

$ cat burncpu.cpp
#include <dlfcn.h>

int main() {
void* handle = dlopen("./dso.so", RTLD_LAZY);
if (!handle) return -1;

typedef void (*fp)();
fp do_nothing = (fp) dlsym(handle, "do_nothing");

while(1) {
do_nothing();
}
}

$ cat dso.cpp
extern "C" void do_nothing() {}

$ cat build.sh
#!/bin/bash
g++ -shared dso.cpp -o dso.so
g++ burncpu.cpp -o burncpu -ldl

I sampled the execution of this program with perf record -b.

Using the existing "brstack,dso", we get absolute addresses that are
affected by ASLR, and could be different on different hosts. The address
does not uniquely identify a branch/target in the binary:

$ perf script -F brstack,dso | sed 's/\/0 /\/0\n/g' | grep burncpu | grep dso.so | head -n 1
0x7f967139b6aa(/tmp/burncpu/dso.so)/0x4006b1(/tmp/burncpu/exe)/P/-/-/0

Using the existing "brstacksym,dso" is a little better, because the
symbol plus offset and dso name *does* uniquely identify a branch/target
in the binary. Ultimately, however, AutoFDO wants a simple offset into
the binary, so we'd have to undo all the work perf did to symbolize in
the first place:

$ perf script -F brstacksym,dso | sed 's/\/0 /\/0\n/g' | grep burncpu | grep dso.so | head -n 1
do_nothing+0x5(/tmp/burncpu/dso.so)/main+0x44(/tmp/burncpu/exe)/P/-/-/0

With the new "brstackoff,dso" we get what we need: a simple offset into a
specific dso/binary that uniquely identifies a branch/target:
$ perf script -F brstackoff,dso | sed 's/\/0 /\/0\n/g' | grep burncpu | grep dso.so | head -n 1
0x6aa(/tmp/burncpu/dso.so)/0x4006b1(/tmp/burncpu/exe)/P/-/-/0

Signed-off-by: Mark Santaniello <marksan@fb.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20170619163825.2012979-2-marksan@fb.com
[ Updated documentation about 'brstackoff' using text from above ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/Documentation/perf-script.txt | 4 ++-
tools/perf/builtin-script.c | 56 +++++++++++++++++++++++++++++---
2 files changed, 55 insertions(+), 5 deletions(-)

diff --git a/tools/perf/Documentation/perf-script.txt b/tools/perf/Documentation/perf-script.txt
index 3eca8c0d3c7b..e2468ed6a307 100644
--- a/tools/perf/Documentation/perf-script.txt
+++ b/tools/perf/Documentation/perf-script.txt
@@ -116,7 +116,7 @@ OPTIONS
--fields::
Comma separated list of fields to print. Options are:
comm, tid, pid, time, cpu, event, trace, ip, sym, dso, addr, symoff,
- srcline, period, iregs, brstack, brstacksym, flags, bpf-output, brstackinsn,
+ srcline, period, iregs, brstack, brstacksym, flags, bpf-output, brstackinsn, brstackoff,
callindent, insn, insnlen. Field list can be prepended with the type, trace, sw or hw,
to indicate to which event type the field list applies.
e.g., -F sw:comm,tid,time,ip,sym and -F trace:time,cpu,trace
@@ -211,6 +211,8 @@ OPTIONS
is printed. This is the full execution path leading to the sample. This is only supported when the
sample was recorded with perf record -b or -j any.

+ The brstackoff field will print an offset into a specific dso/binary.
+
-k::
--vmlinux=<file>::
vmlinux pathname
diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
index 3c21089f5273..db5261c3f719 100644
--- a/tools/perf/builtin-script.c
+++ b/tools/perf/builtin-script.c
@@ -85,6 +85,7 @@ enum perf_output_field {
PERF_OUTPUT_INSN = 1U << 21,
PERF_OUTPUT_INSNLEN = 1U << 22,
PERF_OUTPUT_BRSTACKINSN = 1U << 23,
+ PERF_OUTPUT_BRSTACKOFF = 1U << 24,
};

struct output_option {
@@ -115,6 +116,7 @@ struct output_option {
{.str = "insn", .field = PERF_OUTPUT_INSN},
{.str = "insnlen", .field = PERF_OUTPUT_INSNLEN},
{.str = "brstackinsn", .field = PERF_OUTPUT_BRSTACKINSN},
+ {.str = "brstackoff", .field = PERF_OUTPUT_BRSTACKOFF},
};

/* default set to maintain compatibility with current format */
@@ -299,10 +301,9 @@ static int perf_evsel__check_attr(struct perf_evsel *evsel,
return -EINVAL;
}
if (PRINT_FIELD(DSO) && !PRINT_FIELD(IP) && !PRINT_FIELD(ADDR) &&
- !PRINT_FIELD(BRSTACK) && !PRINT_FIELD(BRSTACKSYM)) {
- pr_err("Display of DSO requested but none of sample IP, sample address, "
- "brstack\nor brstacksym are selected. Hence, no addresses to "
- "convert to DSO.\n");
+ !PRINT_FIELD(BRSTACK) && !PRINT_FIELD(BRSTACKSYM) && !PRINT_FIELD(BRSTACKOFF)) {
+ pr_err("Display of DSO requested but no address to convert. Select\n"
+ "sample IP, sample address, brstack, brstacksym, or brstackoff.\n");
return -EINVAL;
}
if (PRINT_FIELD(SRCLINE) && !PRINT_FIELD(IP)) {
@@ -606,6 +607,51 @@ static void print_sample_brstacksym(struct perf_sample *sample,
}
}

+static void print_sample_brstackoff(struct perf_sample *sample,
+ struct thread *thread,
+ struct perf_event_attr *attr)
+{
+ struct branch_stack *br = sample->branch_stack;
+ struct addr_location alf, alt;
+ u64 i, from, to;
+
+ if (!(br && br->nr))
+ return;
+
+ for (i = 0; i < br->nr; i++) {
+
+ memset(&alf, 0, sizeof(alf));
+ memset(&alt, 0, sizeof(alt));
+ from = br->entries[i].from;
+ to = br->entries[i].to;
+
+ thread__find_addr_map(thread, sample->cpumode, MAP__FUNCTION, from, &alf);
+ if (alf.map && !alf.map->dso->adjust_symbols)
+ from = map__map_ip(alf.map, from);
+
+ thread__find_addr_map(thread, sample->cpumode, MAP__FUNCTION, to, &alt);
+ if (alt.map && !alt.map->dso->adjust_symbols)
+ to = map__map_ip(alt.map, to);
+
+ printf("0x%"PRIx64, from);
+ if (PRINT_FIELD(DSO)) {
+ printf("(");
+ map__fprintf_dsoname(alf.map, stdout);
+ printf(")");
+ }
+ printf("/0x%"PRIx64, to);
+ if (PRINT_FIELD(DSO)) {
+ printf("(");
+ map__fprintf_dsoname(alt.map, stdout);
+ printf(")");
+ }
+ printf("/%c/%c/%c/%d ",
+ mispred_str(br->entries + i),
+ br->entries[i].flags.in_tx ? 'X' : '-',
+ br->entries[i].flags.abort ? 'A' : '-',
+ br->entries[i].flags.cycles);
+ }
+}
#define MAXBB 16384UL

static int grab_bb(u8 *buffer, u64 start, u64 end,
@@ -1227,6 +1273,8 @@ static void process_event(struct perf_script *script,
print_sample_brstack(sample, thread, attr);
else if (PRINT_FIELD(BRSTACKSYM))
print_sample_brstacksym(sample, thread, attr);
+ else if (PRINT_FIELD(BRSTACKOFF))
+ print_sample_brstackoff(sample, thread, attr);

if (perf_evsel__is_bpf_output(evsel) && PRINT_FIELD(BPF_OUTPUT))
print_sample_bpf_output(sample);
--
2.9.4