[tor-bugs] #7305 [Tor]: enum variables with defined bit width

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#7305: enum variables with defined bit width
-----------------------+----------------------------------------------------
 Reporter:  ultramage  |          Owner:     
     Type:  defect     |         Status:  new
 Priority:  normal     |      Milestone:     
Component:  Tor        |        Version:     
 Keywords:  msvc       |         Parent:     
   Points:             |   Actualpoints:     
-----------------------+----------------------------------------------------
 The signedness of an enum type according to the C standard is
 implementation-defined, and thus shouldn't be relied on. However, the code
 implicitly assumes it's unsigned (a gcc-specific thing?), and uses
 constructs like this:
 {{{
 typedef enum {
   ADDR_POLICY_ACCEPT=1,
   ADDR_POLICY_REJECT=2,
 } addr_policy_action_t;

 addr_policy_action_t policy_type:2;
 }}}

 What happens to the above case with the MSVC compiler is that it treats
 the enum type as signed, and writing a '2' makes two's-complement math
 kick in, so '2' becomes '-2'. One unit test fails because of this, which
 is how I noticed it. The consequence is that Tor's state can easily
 destabilize, and impossible execution paths like this could occur:
 {{{
 test = 2;
 assert( test == 2 ); // triggers
 }}}

 There are workarounds, like wrapping the enum in a struct (very ugly), or
 using an integer type for storage (loss of type info). Ideally stop using
 bit packing entirely in memory-only structures, and serialize to integer
 types of exact size when crafting packets (an enum's size is variable in
 gcc, fixed in msvc).

 Here's a list of all offending places for patterns ":N" and ": N", N=1..9:
  * circ_id_type_t circ_id_type:2;
  * addr_policy_action_t policy_type:2;
  * path_state_t path_state : 2;
  * addressmap_entry_source_t source:3;
  * } state : 3;
  * } dir_spool_src : 3;
  * saved_location_t saved_location : 3;

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/7305>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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