Re: [PATCH 4/6] perf thread-stack: Represent jmps to the start of a different symbol

Adrian Hunter
2019-02-06T13:27:09Z

On 6/02/19 2:39 PM, Arnaldo Carvalho de Melo wrote:
> Em Wed, Jan 09, 2019 at 11:18:33AM +0200, Adrian Hunter escreveu:
>> The compiler might optimize a call/ret combination by making it a jmp.
>> However the thread-stack does not presently cater for that, so that such
>> control flow is not visible in the call graph. Make it visible by recording
>> on the stack a branch to the start of a different symbol. Note, that means
>> when a ret pops the stack, all jmps must be popped off first.
>>
>> Example:
>>
>> $ cat jmp-to-fn.c
>> __attribute__((noinline)) int bar(void)
>> {
>> return -1;
>> }
>>
>> __attribute__((noinline)) int foo(void)
>> {
>> return bar() + 1;
>> }
>>
>> int main()
>> {
>> return foo();
>> }
>> $ gcc -ggdb3 -Wall -Wextra -O2 -o jmp-to-fn jmp-to-fn.c
>> $ objdump -d jmp-to-fn
>> <SNIP>
>> 0000000000001040 :
>> 1040: 31 c0 xor %eax,%eax
>> 1042: e9 09 01 00 00 jmpq 1150 <foo>
>> <SNIP>
>> 0000000000001140 <bar>:
>> 1140: b8 ff ff ff ff mov $0xffffffff,%eax
>> 1145: c3 retq
>> <SNIP>
>> 0000000000001150 <foo>:
>> 1150: 31 c0 xor %eax,%eax
>> 1152: e8 e9 ff ff ff callq 1140 <bar>
>> 1157: 83 c0 01 add $0x1,%eax
>> 115a: c3 retq
>> <SNIP>
>> $ perf record -o jmp-to-fn.perf.data -e intel_pt/cyc/u ./jmp-to-fn
>> [ perf record: Woken up 1 times to write data ]
>> [ perf record: Captured and wrote 0,017 MB jmp-to-fn.perf.data ]
>> $ perf script -i jmp-to-fn.perf.data --itrace=be -s ~/libexec/perf-core/scripts/python/export-to-sqlite.py jmp-to-fn.db branches calls
>> 2019-01-08 13:24:58.783069 Creating database...
>> 2019-01-08 13:24:58.794650 Writing records...
>> 2019-01-08 13:24:59.008050 Adding indexes
>> 2019-01-08 13:24:59.015802 Done
>> $ ~/libexec/perf-core/scripts/python/exported-sql-viewer.py jmp-to-fn.db
>
> So, while testing this I notice that we need to do the python3
> conversions for these scripts as well:

I will look at it, but an you take these patches as they are for now?

>
> [acme@quaco adrian]$ objdump -d jmp-to-fn > /tmp/bla
> [acme@quaco adrian]$ vim /tmp/bla
> [acme@quaco adrian]$ perf record -o jmp-to-fn.perf.data -e intel_pt/cyc/u ./jmp-to-fn
> Couldn't synthesize bpf events.
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.017 MB jmp-to-fn.perf.data ]
> [acme@quaco adrian]$ perf script -i jmp-to-fn.perf.data --itrace=be -s ~/libexec/perf-core/scripts/python/export-to-sqlite.py jmp-to-fn.db branches calls
> File "/home/acme/libexec/perf-core/scripts/python/export-to-sqlite.py", line 103
> print datetime.datetime.today(), "Creating database..."
> ^
> SyntaxError: invalid syntax
> Error running python script /home/acme/libexec/perf-core/scripts/python/export-to-sqlite.py
> [acme@quaco adrian]$
>
> Mostly are simple, i.e. in this case we need something like:
>
> print(str(datetime.datetime.today()) + "Creating database...")
>
>
> for a really crude conversion, but one that would make this work with
> both python2 and python3 (make PYTHON=python3 when building perf).
>
>
>> Before:
>>
>> main
>> -> bar
>>
>> After:
>>
>> main
>> -> foo
>> -> bar
>>
>> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
>> ---
>> .../scripts/python/export-to-postgresql.py | 2 +-
>> tools/perf/scripts/python/export-to-sqlite.py | 2 +-
>> tools/perf/util/thread-stack.c | 30 +++++++++++++++++--
>> tools/perf/util/thread-stack.h | 3 ++
>> 4 files changed, 33 insertions(+), 4 deletions(-)
>>
>> diff --git a/tools/perf/scripts/python/export-to-postgresql.py b/tools/perf/scripts/python/export-to-postgresql.py
>> index 0564dd7377f2..30130213da7e 100644
>> --- a/tools/perf/scripts/python/export-to-postgresql.py
>> +++ b/tools/perf/scripts/python/export-to-postgresql.py
>> @@ -478,7 +478,7 @@ if perf_db_export_calls:
>> 'branch_count,'
>> 'call_id,'
>> 'return_id,'
>> - 'CASE WHEN flags=1 THEN \'no call\' WHEN flags=2 THEN \'no return\' WHEN flags=3 THEN \'no call/return\' ELSE \'\' END AS flags,'
>> + 'CASE WHEN flags=0 THEN \'\' WHEN flags=1 THEN \'no call\' WHEN flags=2 THEN \'no return\' WHEN flags=3 THEN \'no call/return\' WHEN flags=6 THEN \'jump\' ELSE flags END AS flags,'
>> 'parent_call_path_id'
>> ' FROM calls INNER JOIN call_paths ON call_paths.id = call_path_id')
>>
>> diff --git a/tools/perf/scripts/python/export-to-sqlite.py b/tools/perf/scripts/python/export-to-sqlite.py
>> index 245caf2643ed..ed237f2ed03f 100644
>> --- a/tools/perf/scripts/python/export-to-sqlite.py
>> +++ b/tools/perf/scripts/python/export-to-sqlite.py
>> @@ -320,7 +320,7 @@ if perf_db_export_calls:
>> 'branch_count,'
>> 'call_id,'
>> 'return_id,'
>> - 'CASE WHEN flags=1 THEN \'no call\' WHEN flags=2 THEN \'no return\' WHEN flags=3 THEN \'no call/return\' ELSE \'\' END AS flags,'
>> + 'CASE WHEN flags=0 THEN \'\' WHEN flags=1 THEN \'no call\' WHEN flags=2 THEN \'no return\' WHEN flags=3 THEN \'no call/return\' WHEN flags=6 THEN \'jump\' ELSE flags END AS flags,'
>> 'parent_call_path_id'
>> ' FROM calls INNER JOIN call_paths ON call_paths.id = call_path_id')
>>
>> diff --git a/tools/perf/util/thread-stack.c b/tools/perf/util/thread-stack.c
>> index 7f8eff018c16..f52c0f90915d 100644
>> --- a/tools/perf/util/thread-stack.c
>> +++ b/tools/perf/util/thread-stack.c
>> @@ -38,6 +38,7 @@
>> * @cp: call path
>> * @no_call: a 'call' was not seen
>> * @trace_end: a 'call' but trace ended
>> + * @non_call: a branch but not a 'call' to the start of a different symbol
>> */
>> struct thread_stack_entry {
>> u64 ret_addr;
>> @@ -47,6 +48,7 @@ struct thread_stack_entry {
>> struct call_path *cp;
>> bool no_call;
>> bool trace_end;
>> + bool non_call;
>> };
>>
>> /**
>> @@ -268,6 +270,8 @@ static int thread_stack__call_return(struct thread *thread,
>> cr.flags |= CALL_RETURN_NO_CALL;
>> if (no_return)
>> cr.flags |= CALL_RETURN_NO_RETURN;
>> + if (tse->non_call)
>> + cr.flags |= CALL_RETURN_NON_CALL;
>>
>> return crp->process(&cr, crp->data);
>> }
>> @@ -510,6 +514,7 @@ static int thread_stack__push_cp(struct thread_stack *ts, u64 ret_addr,
>> tse->cp = cp;
>> tse->no_call = no_call;
>> tse->trace_end = trace_end;
>> + tse->non_call = false;
>>
>> return 0;
>> }
>> @@ -531,14 +536,16 @@ static int thread_stack__pop_cp(struct thread *thread, struct thread_stack *ts,
>> timestamp, ref, false);
>> }
>>
>> - if (ts->stack[ts->cnt - 1].ret_addr == ret_addr) {
>> + if (ts->stack[ts->cnt - 1].ret_addr == ret_addr &&
>> + !ts->stack[ts->cnt - 1].non_call) {
>> return thread_stack__call_return(thread, ts, --ts->cnt,
>> timestamp, ref, false);
>> } else {
>> size_t i = ts->cnt - 1;
>>
>> while (i--) {
>> - if (ts->stack[i].ret_addr != ret_addr)
>> + if (ts->stack[i].ret_addr != ret_addr ||
>> + ts->stack[i].non_call)
>> continue;
>> i += 1;
>> while (ts->cnt > i) {
>> @@ -757,6 +764,25 @@ int thread_stack__process(struct thread *thread, struct comm *comm,
>> err = thread_stack__trace_begin(thread, ts, sample->time, ref);
>> } else if (sample->flags & PERF_IP_FLAG_TRACE_END) {
>> err = thread_stack__trace_end(ts, sample, ref);
>> + } else if (sample->flags & PERF_IP_FLAG_BRANCH &&
>> + from_al->sym != to_al->sym && to_al->sym &&
>> + to_al->addr == to_al->sym->start) {
>> + struct call_path_root *cpr = ts->crp->cpr;
>> + struct call_path *cp;
>> +
>> + /*
>> + * The compiler might optimize a call/ret combination by making
>> + * it a jmp. Make that visible by recording on the stack a
>> + * branch to the start of a different symbol. Note, that means
>> + * when a ret pops the stack, all jmps must be popped off first.
>> + */
>> + cp = call_path__findnew(cpr, ts->stack[ts->cnt - 1].cp,
>> + to_al->sym, sample->addr,
>> + ts->kernel_start);
>> + err = thread_stack__push_cp(ts, 0, sample->time, ref, cp, false,
>> + false);
>> + if (!err)
>> + ts->stack[ts->cnt - 1].non_call = true;
>> }
>>
>> return err;
>> diff --git a/tools/perf/util/thread-stack.h b/tools/perf/util/thread-stack.h
>> index 1f626f4a1c40..b7c04e19ad41 100644
>> --- a/tools/perf/util/thread-stack.h
>> +++ b/tools/perf/util/thread-stack.h
>> @@ -35,10 +35,13 @@ struct call_path;
>> *
>> * CALL_RETURN_NO_CALL: 'return' but no matching 'call'
>> * CALL_RETURN_NO_RETURN: 'call' but no matching 'return'
>> + * CALL_RETURN_NON_CALL: a branch but not a 'call' to the start of a different
>> + * symbol
>> */
>> enum {
>> CALL_RETURN_NO_CALL = 1 << 0,
>> CALL_RETURN_NO_RETURN = 1 << 1,
>> + CALL_RETURN_NON_CALL = 1 << 2,
>> };
>>
>> /**
>> --
>> 2.17.1
>