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Backtraces are broken on OSX #7821

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staticfloat opened this issue Aug 3, 2014 · 17 comments
Closed

Backtraces are broken on OSX #7821

staticfloat opened this issue Aug 3, 2014 · 17 comments
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@Keno
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bug Indicates an unexpected problem or unintended behavior system:mac Affects only macOS

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@staticfloat
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Well this is new. Backtraces appear to be broken on OSX, but only for C code. Example with my favorite call graph exploration utility @profile:

julia> @profile peakflops()
1.6386590022993734e10

julia> Profile.print()
33 task.jl; anonymous; line: 96
 32 REPL.jl; eval_user_input; line: 54
  32 profile.jl; anonymous; line: 14
   32 linalg/generic.jl; peakflops; line: 324
    5  linalg/generic.jl; peakflops; line: 69
     5 linalg/matmul.jl; gemm_wrapper!; line: 285
      5 linalg/blas.jl; gemm!; line: 526
    27 linalg/generic.jl; peakflops; line: 326
     27 random.jl; rand!; line: 129
 1  REPL.jl; eval_user_input; line: 55

julia> Profile.print(C=true)
...
33 ???; ???; line: 92035753
 33 ???; ???; line: 92041358
  33 task.jl; anonymous; line: 96
   33 ???; ???; line: 91703924
    33 ???; ???; line: 113759015
     32 REPL.jl; eval_user_input; line: 54
      32 ???; ???; line: 91725559
       32 ???; ???; line: 92069246
        32 profile.jl; anonymous; line: 14
         32 linalg/generic.jl; peakflops; line: 324
          5  linalg/generic.jl; peakflops; line: 69
           5 linalg/matmul.jl; gemm_wrapper!; line: 285
            5 linalg/blas.jl; gemm!; line: 526
             5 ???; ???; line: 131770600
              5 ???; ???; line: 133001818
               5 ???; ???; line: 133002515
                5 ???; ???; line: 134195766
                 4 ???; ???; line: 133003899
                  1 ???; ???; line: 153704009
                  1 ???; ???; line: 153704064
                  1 ???; ???; line: 153704084
...

This is running on:

julia> versioninfo()
Julia Version 0.3.0-rc1+314
Commit e8e461e* (2014-08-02 21:40 UTC)
Platform Info:
  System: Darwin (x86_64-apple-darwin13.3.0)
  CPU: Intel(R) Core(TM) i5-4258U CPU @ 2.40GHz
  WORD_SIZE: 64
  BLAS: libopenblas (USE64BITINT DYNAMIC_ARCH NO_AFFINITY Haswell)
  LAPACK: libopenblas
  LIBM: libopenlibm
  LLVM: libLLVM-3.3
@staticfloat staticfloat added the mac label Aug 3, 2014
@Keno
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Keno commented Aug 3, 2014

Working on it.

@Keno
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Keno commented Aug 3, 2014

Actually, never mind. This issue is simple. You need the .dSYM files for libjulia. Try dsymutil libjulia.dylib.

@Keno
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Keno commented Aug 3, 2014

I suppose we should give you approximations to the backtrace (function names only, no line numbers), if the debug info is not available.

@staticfloat
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I ran dsymutil on libjulia.dylib and libjulia-debug.dylib, but that didn't fix it. I deleted the .dSYM files in case they had been there before and I didn't notice it, re-ran dsymutil, and that didn't fix it either.

@Keno
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Keno commented Aug 3, 2014

Ok, will have another look.

@JeffBezanson
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Same thing on linux. We should also print nothing instead of the ??? and crazy numbers.

@Keno
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Keno commented Aug 3, 2014

Ok, there is a similar issue with profiling in that I/O time is not reported properly on OS X because our unwinder fails miserably (also potentially a problem for ^C and one of the reasons we can segfault in I/O):

julia> @profile sleep(10)

julia> Profile.print(C=true)
8399 ???; ???; line: -1794431414

Just noting it down while we're talking about backtraces. I'll have a look at the other issue though.

@staticfloat
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While working on the tests/netload/ltests.jl stuff, I've found that I can get segfaults a pretty good chunk of the time when waiting on I/O code as well. I'll try to make some reproducible test cases and submit them as issues.

@Keno
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Keno commented Aug 3, 2014

Ok, so this turns out to be mostly easy. I'll enable debug symbols in the release binaries and add a fallback mode that finds the function but bails on line numbers.

@staticfloat
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I should note that the debug build fares much better, but is not perfect:

$ cat test.jl
@profile peakflops()
Profile.print(C=true)
$ julia test.jl
37 ???; ???; line: 262313206
 37 ...e/src/julia/src/task.c; rec_backtrace_ctx; line: 606
  37 ???; ???; line: 262311876
   37 ???; ???; line: 262312789
    37 ...e/src/julia/src/gf.c; jl_gf_invoke; line: 1489
     37 ...e/src/julia/src/gf.c; jl_method_list_insert; line: 1121
      37 ...julia/src/builtins.c; jl_f_union; line: 846
       37 ...ulia/src/builtins.c; jl_f_top_eval; line: 406
        37 ???; ???; line: 290817769
         37 ./client.jl; _start; line: 354
          37 ./client.jl; process_options; line: 285
           37 ...rc/julia/src/gf.c; jl_gf_invoke; line: 1509
            37 ...rc/julia/src/gf.c; jl_method_list_insert; line: 1121
             37 ...ia/src/builtins.c; jl_f_union; line: 846
              37 ...ia/src/builtins.c; jl_f_top_eval; line: 406
               37 loading.jl; include_from_node1; line: 128
                37 .../julia/src/gf.c; jl_gf_invoke; line: 1489
                 37 .../julia/src/gf.c; jl_method_list_insert; line: 1121
                  37 ./boot.jl; include; line: 245
                   37 .../src/toplevel.c; jl_method_def; line: 709
                    37 ...src/toplevel.c; jl_method_def; line: 703
                     1  ...src/toplevel.c; jl_method_def; line: 682
                      1 ...ulia/src/ast.c; jl_lam_args; line: 603
                       1 ...flisp/./read.c; strtoull_0b0o; line: 24
                        1 ...lisp/./read.c; isnumtok_base; line: 73
                         1 ..././cvalues.c; fl_neg; line: 1021
                          1 ..././cvalues.c; cvalue_relocate; line: 562
                           1 ..../cvalues.c; fl_neg; line: 1021
                            1 ..../cvalues.c; cvalue_relocate; line: 562
                             1 ...isp/flisp.c; apply_cl; line: 1220
                     36 ...src/toplevel.c; jl_method_def; line: 690
                      36 ...rc/toplevel.c; jl_is_toplevel_only_expr; line: 363
                       36 ...rc/toplevel.c; jl_method_def; line: 673
                        36 ...rc/builtins.c; jl_f_union; line: 846
                         36 ...c/builtins.c; jl_f_top_eval; line: 406
                          36 profile.jl; anonymous; line: 14
                           36 .../generic.jl; peakflops; line: 324
                            8  .../generic.jl; peakflops; line: 69
                             8 ...g/matmul.jl; gemm_wrapper!; line: 285
                              8 linalg/blas.jl; gemm!; line: 526
                               8 ???; ???; line: 303835368
                                8 ???; ???; line: 305066586
                                 8 ???; ???; line: 305067283
                                  8 ???; ???; line: 306260534
                                   4 ???; ???; line: 305068667
                                    1 ???; ???; line: 325768730
                                    1 ???; ???; line: 325768756
                                    1 ???; ???; line: 325768832
                                    1 ???; ???; line: 325768852
                                   4 ???; ???; line: 305069442
                                    1 ???; ???; line: 325770121
                                    2 ???; ???; line: 325770131
                                    1 ???; ???; line: 325770157
                            28 .../generic.jl; peakflops; line: 326
                             28 random.jl; rand!; line: 129
                              2 ???; ???; line: 409812660
                              1 ???; ???; line: 409812752
                              1 ???; ???; line: 409812760
                              1 ???; ???; line: 409812777
                              1 ???; ???; line: 409812781
                              2 ???; ???; line: 409812825
                              3 ???; ???; line: 409812833
                              2 ???; ???; line: 409812841
1  ???; ???; line: 325754199
1  ???; ???; line: 325754246
1  ???; ???; line: 325754473
1  ???; ???; line: 325754590
... (many more lines)

@timholy
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timholy commented Aug 3, 2014

I noticed this on Linux ever since I upgraded to Kubuntu 14.04. It was better on 12.04.

@Keno Keno self-assigned this Aug 3, 2014
@Keno Keno closed this as completed in b26ff92 Aug 3, 2014
@timholy
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timholy commented Aug 3, 2014

It's working fine for me locally, and wow is this a nice improvement!

But very curiously it looks like this has Travis failures. It's not finding ucontext_t. Travis is running Ubuntu 12.04, so maybe the header files are different. Do we need to #include <ucontext.h>?

@Keno
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Keno commented Aug 3, 2014

Fixed in the next commit.

@timholy
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timholy commented Aug 3, 2014

I should have checked. Thanks.

@staticfloat
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@Keno wow, this is so much better. Thank you!

Just one final note, there is still a single ??? line when running @profile peakflops():

julia> Profile.print(C=true)
30  ...sabae/src/julia/./julia; main; (unknown line)
 30 .../src/julia/src/init.c; julia_trampoline; line: 1002
  30 .../src/julia/src/task.c; jl_handle_stack_switch; line: 434
   30 .../src/julia/src/task.c; jl_switch_stack; line: 217
    30 .../src/julia/src/task.c; switch_stack; line: 209
     30 ...src/julia/src/task.c; start_task; line: 426
      30 .../julia/src/./julia.h; jl_apply; line: 975
       30 ...ulia/src/builtins.c; jl_trampoline; line: 786
        30 ...julia/src/./julia.h; jl_apply; line: 975
         30 task.jl; anonymous; line: 96
          30 ...src/julia/src/gf.c; jl_apply_generic; line: 1428
           30 ...ulia/src/./julia.h; jl_apply; line: 975
            30 ...ia/src/builtins.c; jl_trampoline; line: 786
             30 ...lia/src/./julia.h; jl_apply; line: 975
              30 ???; ???; line: 176047015
               29 REPL.jl; eval_user_input; line: 54
                29 ...a/src/builtins.c; jl_f_top_eval; line: 396
                 29 .../src/toplevel.c; jl_toplevel_eval; line: 516
...

Looking at show_backtrace(), I see there's some special handling of eval_user_input, could that have anything to do with this?

@JeffBezanson
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In the case where we print the instruction pointer, we should print ip = #### instead of line:. Handling unknown locations more gracefully will make it look much less buggy.

@Keno
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Keno commented Aug 4, 2014

Yep, will do. I do think I can fix this one though.

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@staticfloat @JeffBezanson @Keno @timholy