[GHC] #11489: Segmentation fault when .prof file not writeable

[GHC]

#11489: Segmentation fault when .prof file not writeable
-------------------------------------+-------------------------------------
        Reporter:  thomie            |                Owner:  thomie
            Type:  bug               |               Status:  new
        Priority:  low               |            Milestone:  8.0.1
       Component:  Profiling         |              Version:  7.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #7149             |  Differential Rev(s):  Phab:D1849
       Wiki Page:                    |
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Comment (by Thomas Miedema <thomasmiedema@…>):

 In [changeset:"6d2bdfd8d40b926d7a11d003213220022a63d9f5/ghc"
 6d2bdfd8/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="6d2bdfd8d40b926d7a11d003213220022a63d9f5"
 Fix segmentation fault when .prof file not writeable

 There are two ways to do retainer profiling. Quoting from the user's
 guide:
   1. `+RTS -hr` "Breaks down the graph by retainer set"
   2. `+RTS -hr<cc> -h<x>`, where `-h<x>` is one of normal heap profiling
      break-down options (e.g. `-hc`), and `-hr<cc> means "Restrict the
      profile to closures with retainer sets containing cost-centre
      stacks with one of the specified cost centres at the top."

 Retainer profiling writes to a .hp file, like the other heap profiling
 options, but also to a .prof file. Therefore, when the .prof file is not
 writeable for whatever reason, retainer profiling should be turned off
 completely.

 This worked ok when running the program with `+RTS -hr` (option 1), but a
 segfault would occur when using `+RTS -hr<cc> -h<x>`, with `x!=r` (option
 2).

 This commit fixes that.

 Reviewed by: bgamari

 Differential Revision: https://phabricator.haskell.org/D1849

 GHC Trac Issues: #11489
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11489#comment:4>
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