releases/3.18.134/perf-unwind-take-pgoff-into-account-when-reporting-e.patch

   1 From 02cdb4e7c4828e9d3965f9192b21ec7e27310c57 Mon Sep 17 00:00:00 2001
   2 From: Milian Wolff <milian.wolff@kdab.com>
   3 Date: Mon, 29 Oct 2018 15:16:44 +0100
   4 Subject: perf unwind: Take pgoff into account when reporting elf to libdwfl
   5
   6 [ Upstream commit 1fe627da30331024f453faef04d500079b901107 ]
   7
   8 libdwfl parses an ELF file itself and creates mappings for the
   9 individual sections. perf on the other hand sees raw mmap events which
  10 represent individual sections. When we encounter an address pointing
  11 into a mapping with pgoff != 0, we must take that into account and
  12 report the file at the non-offset base address.
  13
  14 This fixes unwinding with libdwfl in some cases. E.g. for a file like:
  15
  16 ```
  17
  18 using namespace std;
  19
  20 mutex g_mutex;
  21
  22 double worker()
  23 {
  24     lock_guard<mutex> guard(g_mutex);
  25     uniform_real_distribution<double> uniform(-1E5, 1E5);
  26     default_random_engine engine;
  27     double s = 0;
  28     for (int i = 0; i < 1000; ++i) {
  29         s += norm(complex<double>(uniform(engine), uniform(engine)));
  30     }
  31     cout << s << endl;
  32     return s;
  33 }
  34
  35 int main()
  36 {
  37     vector<std::future<double>> results;
  38     for (int i = 0; i < 10000; ++i) {
  39         results.push_back(async(launch::async, worker));
  40     }
  41     return 0;
  42 }
  43 ```
  44
  45 Compile it with `g++ -g -O2 -lpthread cpp-locking.cpp  -o cpp-locking`,
  46 then record it with `perf record --call-graph dwarf -e
  47 sched:sched_switch`.
  48
  49 When you analyze it with `perf script` and libunwind, you should see:
  50
  51 ```
  52 cpp-locking 20038 [005] 54830.236589: sched:sched_switch: prev_comm=cpp-locking prev_pid=20038 prev_prio=120 prev_state=T ==> next_comm=swapper/5 next_pid=0 next_prio=120
  53         ffffffffb166fec5 __sched_text_start+0x545 (/lib/modules/4.14.78-1-lts/build/vmlinux)
  54         ffffffffb166fec5 __sched_text_start+0x545 (/lib/modules/4.14.78-1-lts/build/vmlinux)
  55         ffffffffb1670208 schedule+0x28 (/lib/modules/4.14.78-1-lts/build/vmlinux)
  56         ffffffffb16737cc rwsem_down_read_failed+0xec (/lib/modules/4.14.78-1-lts/build/vmlinux)
  57         ffffffffb1665e04 call_rwsem_down_read_failed+0x14 (/lib/modules/4.14.78-1-lts/build/vmlinux)
  58         ffffffffb1672a03 down_read+0x13 (/lib/modules/4.14.78-1-lts/build/vmlinux)
  59         ffffffffb106bd85 __do_page_fault+0x445 (/lib/modules/4.14.78-1-lts/build/vmlinux)
  60         ffffffffb18015f5 page_fault+0x45 (/lib/modules/4.14.78-1-lts/build/vmlinux)
  61             7f38e4252591 new_heap+0x101 (/usr/lib/libc-2.28.so)
  62             7f38e4252d0b arena_get2.part.4+0x2fb (/usr/lib/libc-2.28.so)
  63             7f38e4255b1c tcache_init.part.6+0xec (/usr/lib/libc-2.28.so)
  64             7f38e42569e5 __GI___libc_malloc+0x115 (inlined)
  65             7f38e4241790 __GI__IO_file_doallocate+0x90 (inlined)
  66             7f38e424fbbf __GI__IO_doallocbuf+0x4f (inlined)
  67             7f38e424ee47 __GI__IO_file_overflow+0x197 (inlined)
  68             7f38e424df36 _IO_new_file_xsputn+0x116 (inlined)
  69             7f38e4242bfb __GI__IO_fwrite+0xdb (inlined)
  70             7f38e463fa6d std::basic_streambuf<char, std::char_traits<char> >::sputn(char const*, long)+0x1cd (inlined)
  71             7f38e463fa6d std::ostreambuf_iterator<char, std::char_traits<char> >::_M_put(char const*, long)+0x1cd (inlined)
  72             7f38e463fa6d std::ostreambuf_iterator<char, std::char_traits<char> > std::__write<char>(std::ostreambuf_iterator<char, std::char_traits<char> >, char const*, int)+0x1cd (inlined)
  73             7f38e463fa6d std::ostreambuf_iterator<char, std::char_traits<char> > std::num_put<char, std::ostreambuf_iterator<char, std::char_traits<char> > >::_M_insert_float<double>(std::ostreambuf_iterator<c>
  74             7f38e464bd70 std::num_put<char, std::ostreambuf_iterator<char, std::char_traits<char> > >::put(std::ostreambuf_iterator<char, std::char_traits<char> >, std::ios_base&, char, double) const+0x90 (inl>
  75             7f38e464bd70 std::ostream& std::ostream::_M_insert<double>(double)+0x90 (/usr/lib/libstdc++.so.6.0.25)
  76             563b9cb502f7 std::ostream::operator<<(double)+0xb7 (inlined)
  77             563b9cb502f7 worker()+0xb7 (/ssd/milian/projects/kdab/rnd/hotspot/build/tests/test-clients/cpp-locking/cpp-locking)
  78             563b9cb506fb double std::__invoke_impl<double, double (*)()>(std::__invoke_other, double (*&&)())+0x2b (inlined)
  79             563b9cb506fb std::__invoke_result<double (*)()>::type std::__invoke<double (*)()>(double (*&&)())+0x2b (inlined)
  80             563b9cb506fb decltype (__invoke((_S_declval<0ul>)())) std::thread::_Invoker<std::tuple<double (*)()> >::_M_invoke<0ul>(std::_Index_tuple<0ul>)+0x2b (inlined)
  81             563b9cb506fb std::thread::_Invoker<std::tuple<double (*)()> >::operator()()+0x2b (inlined)
  82             563b9cb506fb std::__future_base::_Task_setter<std::unique_ptr<std::__future_base::_Result<double>, std::__future_base::_Result_base::_Deleter>, std::thread::_Invoker<std::tuple<double (*)()> >, dou>
  83             563b9cb506fb std::_Function_handler<std::unique_ptr<std::__future_base::_Result_base, std::__future_base::_Result_base::_Deleter> (), std::__future_base::_Task_setter<std::unique_ptr<std::__future_>
  84             563b9cb507e8 std::function<std::unique_ptr<std::__future_base::_Result_base, std::__future_base::_Result_base::_Deleter> ()>::operator()() const+0x28 (inlined)
  85             563b9cb507e8 std::__future_base::_State_baseV2::_M_do_set(std::function<std::unique_ptr<std::__future_base::_Result_base, std::__future_base::_Result_base::_Deleter> ()>*, bool*)+0x28 (/ssd/milian/>
  86             7f38e46d24fe __pthread_once_slow+0xbe (/usr/lib/libpthread-2.28.so)
  87             563b9cb51149 __gthread_once+0xe9 (inlined)
  88             563b9cb51149 void std::call_once<void (std::__future_base::_State_baseV2::*)(std::function<std::unique_ptr<std::__future_base::_Result_base, std::__future_base::_Result_base::_Deleter> ()>*, bool*)>
  89             563b9cb51149 std::__future_base::_State_baseV2::_M_set_result(std::function<std::unique_ptr<std::__future_base::_Result_base, std::__future_base::_Result_base::_Deleter> ()>, bool)+0xe9 (inlined)
  90             563b9cb51149 std::__future_base::_Async_state_impl<std::thread::_Invoker<std::tuple<double (*)()> >, double>::_Async_state_impl(std::thread::_Invoker<std::tuple<double (*)()> >&&)::{lambda()#1}::op>
  91             563b9cb51149 void std::__invoke_impl<void, std::__future_base::_Async_state_impl<std::thread::_Invoker<std::tuple<double (*)()> >, double>::_Async_state_impl(std::thread::_Invoker<std::tuple<double>
  92             563b9cb51149 std::__invoke_result<std::__future_base::_Async_state_impl<std::thread::_Invoker<std::tuple<double (*)()> >, double>::_Async_state_impl(std::thread::_Invoker<std::tuple<double (*)()> >>
  93             563b9cb51149 decltype (__invoke((_S_declval<0ul>)())) std::thread::_Invoker<std::tuple<std::__future_base::_Async_state_impl<std::thread::_Invoker<std::tuple<double (*)()> >, double>::_Async_state_>
  94             563b9cb51149 std::thread::_Invoker<std::tuple<std::__future_base::_Async_state_impl<std::thread::_Invoker<std::tuple<double (*)()> >, double>::_Async_state_impl(std::thread::_Invoker<std::tuple<dou>
  95             563b9cb51149 std::thread::_State_impl<std::thread::_Invoker<std::tuple<std::__future_base::_Async_state_impl<std::thread::_Invoker<std::tuple<double (*)()> >, double>::_Async_state_impl(std::thread>
  96             7f38e45f0062 execute_native_thread_routine+0x12 (/usr/lib/libstdc++.so.6.0.25)
  97             7f38e46caa9c start_thread+0xfc (/usr/lib/libpthread-2.28.so)
  98             7f38e42ccb22 __GI___clone+0x42 (inlined)
  99 ```
 100
 101 Before this patch, using libdwfl, you would see:
 102
 103 ```
 104 cpp-locking 20038 [005] 54830.236589: sched:sched_switch: prev_comm=cpp-locking prev_pid=20038 prev_prio=120 prev_state=T ==> next_comm=swapper/5 next_pid=0 next_prio=120
 105         ffffffffb166fec5 __sched_text_start+0x545 (/lib/modules/4.14.78-1-lts/build/vmlinux)
 106         ffffffffb166fec5 __sched_text_start+0x545 (/lib/modules/4.14.78-1-lts/build/vmlinux)
 107         ffffffffb1670208 schedule+0x28 (/lib/modules/4.14.78-1-lts/build/vmlinux)
 108         ffffffffb16737cc rwsem_down_read_failed+0xec (/lib/modules/4.14.78-1-lts/build/vmlinux)
 109         ffffffffb1665e04 call_rwsem_down_read_failed+0x14 (/lib/modules/4.14.78-1-lts/build/vmlinux)
 110         ffffffffb1672a03 down_read+0x13 (/lib/modules/4.14.78-1-lts/build/vmlinux)
 111         ffffffffb106bd85 __do_page_fault+0x445 (/lib/modules/4.14.78-1-lts/build/vmlinux)
 112         ffffffffb18015f5 page_fault+0x45 (/lib/modules/4.14.78-1-lts/build/vmlinux)
 113             7f38e4252591 new_heap+0x101 (/usr/lib/libc-2.28.so)
 114         a041161e77950c5c [unknown] ([unknown])
 115 ```
 116
 117 With this patch applied, we get a bit further in unwinding:
 118
 119 ```
 120 cpp-locking 20038 [005] 54830.236589: sched:sched_switch: prev_comm=cpp-locking prev_pid=20038 prev_prio=120 prev_state=T ==> next_comm=swapper/5 next_pid=0 next_prio=120
 121         ffffffffb166fec5 __sched_text_start+0x545 (/lib/modules/4.14.78-1-lts/build/vmlinux)
 122         ffffffffb166fec5 __sched_text_start+0x545 (/lib/modules/4.14.78-1-lts/build/vmlinux)
 123         ffffffffb1670208 schedule+0x28 (/lib/modules/4.14.78-1-lts/build/vmlinux)
 124         ffffffffb16737cc rwsem_down_read_failed+0xec (/lib/modules/4.14.78-1-lts/build/vmlinux)
 125         ffffffffb1665e04 call_rwsem_down_read_failed+0x14 (/lib/modules/4.14.78-1-lts/build/vmlinux)
 126         ffffffffb1672a03 down_read+0x13 (/lib/modules/4.14.78-1-lts/build/vmlinux)
 127         ffffffffb106bd85 __do_page_fault+0x445 (/lib/modules/4.14.78-1-lts/build/vmlinux)
 128         ffffffffb18015f5 page_fault+0x45 (/lib/modules/4.14.78-1-lts/build/vmlinux)
 129             7f38e4252591 new_heap+0x101 (/usr/lib/libc-2.28.so)
 130             7f38e4252d0b arena_get2.part.4+0x2fb (/usr/lib/libc-2.28.so)
 131             7f38e4255b1c tcache_init.part.6+0xec (/usr/lib/libc-2.28.so)
 132             7f38e42569e5 __GI___libc_malloc+0x115 (inlined)
 133             7f38e4241790 __GI__IO_file_doallocate+0x90 (inlined)
 134             7f38e424fbbf __GI__IO_doallocbuf+0x4f (inlined)
 135             7f38e424ee47 __GI__IO_file_overflow+0x197 (inlined)
 136             7f38e424df36 _IO_new_file_xsputn+0x116 (inlined)
 137             7f38e4242bfb __GI__IO_fwrite+0xdb (inlined)
 138             7f38e463fa6d std::basic_streambuf<char, std::char_traits<char> >::sputn(char const*, long)+0x1cd (inlined)
 139             7f38e463fa6d std::ostreambuf_iterator<char, std::char_traits<char> >::_M_put(char const*, long)+0x1cd (inlined)
 140             7f38e463fa6d std::ostreambuf_iterator<char, std::char_traits<char> > std::__write<char>(std::ostreambuf_iterator<char, std::char_traits<char> >, char const*, int)+0x1cd (inlined)
 141             7f38e463fa6d std::ostreambuf_iterator<char, std::char_traits<char> > std::num_put<char, std::ostreambuf_iterator<char, std::char_traits<char> > >::_M_insert_float<double>(std::ostreambuf_iterator<c>
 142             7f38e464bd70 std::num_put<char, std::ostreambuf_iterator<char, std::char_traits<char> > >::put(std::ostreambuf_iterator<char, std::char_traits<char> >, std::ios_base&, char, double) const+0x90 (inl>
 143             7f38e464bd70 std::ostream& std::ostream::_M_insert<double>(double)+0x90 (/usr/lib/libstdc++.so.6.0.25)
 144             563b9cb502f7 std::ostream::operator<<(double)+0xb7 (inlined)
 145             563b9cb502f7 worker()+0xb7 (/ssd/milian/projects/kdab/rnd/hotspot/build/tests/test-clients/cpp-locking/cpp-locking)
 146         6eab825c1ee3e4ff [unknown] ([unknown])
 147 ```
 148
 149 Note that the backtrace is still stopping too early, when compared to
 150 the nice results obtained via libunwind. It's unclear so far what the
 151 reason for that is.
 152
 153 Committer note:
 154
 155 Further comment by Milian on the thread started on the Link: tag below:
 156
 157  ---
 158 The remaining issue is due to a bug in elfutils:
 159
 160 https://sourceware.org/ml/elfutils-devel/2018-q4/msg00089.html
 161
 162 With both patches applied, libunwind and elfutils produce the same output for
 163 the above scenario.
 164  ---
 165
 166 Signed-off-by: Milian Wolff <milian.wolff@kdab.com>
 167 Acked-by: Jiri Olsa <jolsa@kernel.org>
 168 Link: http://lkml.kernel.org/r/20181029141644.3907-1-milian.wolff@kdab.com
 169 Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
 170 Signed-off-by: Sasha Levin <sashal@kernel.org>
 171 ---
 172  tools/perf/util/unwind-libdw.c |    4 ++--
 173  1 file changed, 2 insertions(+), 2 deletions(-)
 174
 175 --- a/tools/perf/util/unwind-libdw.c
 176 +++ b/tools/perf/util/unwind-libdw.c
 177 @@ -41,13 +41,13 @@ static int __report_module(struct addr_l
 178                 Dwarf_Addr s;
 179
 180                 dwfl_module_info(mod, NULL, &s, NULL, NULL, NULL, NULL, NULL);
 181 -               if (s != al->map->start)
 182 +               if (s != al->map->start - al->map->pgoff)
 183                         mod = 0;
 184         }
 185
 186         if (!mod)
 187                 mod = dwfl_report_elf(ui->dwfl, dso->short_name,
 188 -                                     (dso->symsrc_filename ? dso->symsrc_filename : dso->long_name), -1, al->map->start,
 189 +                                     (dso->symsrc_filename ? dso->symsrc_filename : dso->long_name), -1, al->map->start - al->map->pgoff,
 190                                       false);
 191
 192         return mod && dwfl_addrmodule(ui->dwfl, ip) == mod ? 0 : -1;