[tor-bugs] #13157 [Tor]: [patch] Clang Analyzer: Spurious Warnings 2

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#13157: [patch] Clang Analyzer: Spurious Warnings 2
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 Reporter:  teor       |          Owner:
     Type:  defect     |         Status:  new
 Priority:  minor      |      Milestone:
Component:  Tor        |        Version:  Tor: unspecified
 Keywords:  tor-relay  |  Actual Points:
Parent ID:             |         Points:
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 After #13036 was committed, clang --analyze continued to produce 2
 existing NULL pointer dereference warnings; and 1 new uninitialised
 variable warning. I am compiling tor from git source on OS X.

 == 01-in6-addr32-not-null.patch

 The NULL pointer warnings on the return value of tor_addr_to_in6_addr32()
 are incorrect. But clang can't work this out itself due to limited
 analysis depth. To teach the analyser that the return value is safe to
 dereference, I applied tor_assert to the return value. This assert can
 optionally be wrapped in:
 {{{#!c
 #if !defined(__clang_analyzer__) || PARANOIA
 }}}
 or similar, if performance is an issue in this code. The assertion
 silences the spurious warning.


 == 02-dirserv-init-msg.patch

 At this point in the code, msg has been set to a string constant. But the
 tor code checks that msg is not NULL, and the redundant NULL check
 confuses the analyser:
 {{{#!c
       log_info(LD_DIRSERV, "Router %s is now rejected: %s",
                description, msg?msg:"");
 }}}
 To avoid this spurious warning, the patch initialises msg to NULL.

 == clang --analyze clean!

 Once these patches are applied, tor is clang --analyze clean, except for
 dead stores. (Which I trust the optimiser to remove in most cases.)

 == git version

 These warnings occur in the git source of tor 0.2.6.?-alpha around 14
 September 2014
 e.g. commit d6b2a1709d28c656dadc019fb24145e6ac400771

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/13157>
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