# How to debug a crash?

**URL:** <https://discourse.julialang.org/t/how-to-debug-a-crash/15544>\
**Category:** General Usage\
**Created:** [September 27, 2018, 6:19am UTC](https://discourse.julialang.org/t/how-to-debug-a-crash/15544 "2018-09-27T06:19:58Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![pochoi](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pochoi/32/3742_2.png) [@pochoi](https://discourse.julialang.org/u/pochoi)\
**Post date:** [September 27, 2018, 6:19am UTC](https://discourse.julialang.org/t/how-to-debug-a-crash/15544/1 "2018-09-27T06:19:58Z")

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Meet a crash like this when running certain part of my codes.

```julia
Unreachable reached at 0x11a03de66

signal (4): Illegal instruction: 4
in expression starting at no file:0
top-level scope at ./REPL[17]:2 [inlined]
top-level scope at ./none:0
jl_fptr_trampoline at /Users/osx/buildbot/slave/package_osx64/build/src/gf.c:1829
jl_toplevel_eval_flex at /Users/osx/buildbot/slave/package_osx64/build/src/toplevel.c:825
jl_toplevel_eval_in at /Users/osx/buildbot/slave/package_osx64/build/src/builtins.c:633
eval at ./boot.jl:319
eval_user_input at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v0.7/REPL/src/REPL.jl:85
macro expansion at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v0.7/REPL/src/REPL.jl:117 [inlined]
#28 at ./task.jl:262
jl_apply at /Users/osx/buildbot/slave/package_osx64/build/src/./julia.h:1538 [inlined]
start_task at /Users/osx/buildbot/slave/package_osx64/build/src/task.c:268
Allocations: 58071594 (Pool: 58060526; Big: 11068); GC: 287
Illegal instruction: 4

```

My question is, how to track down the causes of such crash?

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<div class="post-metadata">

**Author:** ![tim.holy](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tim.holy/32/52_2.png) [@tim.holy](https://discourse.julialang.org/u/tim.holy)\
**Post date:** [September 27, 2018, 1:42pm UTC](https://discourse.julialang.org/t/how-to-debug-a-crash/15544/2 "2018-09-27T13:42:43Z")

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The easiest way to (hopefully) fix this is to do a fresh (as of a few hours ago) source build of the `release-1.0` branch of Julia; as advertised [here](https://discourse.julialang.org/t/julia-1-0-1-testing-period/15534) that branch will likely become Julia 1.0.1, and your crash may have already been fixed there.

If that doesn’t fix it, then you really will need to debug it. There are some very helpful [gdb tips in devdocs](https://docs.julialang.org/en/latest/devdocs/debuggingtips/).

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**Author:** ![tobias.knopp](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tobias.knopp/32/7551_2.png) [@tobias.knopp](https://discourse.julialang.org/u/tobias.knopp)\
**Post date:** [September 27, 2018, 1:59pm UTC](https://discourse.julialang.org/t/how-to-debug-a-crash/15544/3 "2018-09-27T13:59:45Z")

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That one is beeing worked on by jeff. See github

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<div class="post-metadata">

**Author:** ![lobingera](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/lobingera/32/211_2.png) [@lobingera](https://discourse.julialang.org/u/lobingera)\
**Post date:** [September 27, 2018, 2:33pm UTC](https://discourse.julialang.org/t/how-to-debug-a-crash/15544/4 "2018-09-27T14:33:01Z")

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> [@tobias.knopp](#):
>
> See github

All github, or a special place, like an issue/PR?

SCNR

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<div class="post-metadata">

**Author:** ![tobias.knopp](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tobias.knopp/32/7551_2.png) [@tobias.knopp](https://discourse.julialang.org/u/tobias.knopp)\
**Post date:** [September 27, 2018, 2:56pm UTC](https://discourse.julialang.org/t/how-to-debug-a-crash/15544/5 "2018-09-27T14:56:58Z")

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[https://github.com/JuliaLang/julia/pull/29380](https://github.com/JuliaLang/julia/pull/29380)

Sorry, I am on the phone and just wanted to inform that this is a known bug