[tor-bugs] #29537 [Core Tor/Tor]: verify intptr_t round-trip through void *

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#29537: verify intptr_t round-trip through void *
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 Reporter:  catalyst                    |          Owner:  (none)
     Type:  defect                      |         Status:  needs_revision
 Priority:  Medium                      |      Milestone:  Tor:
                                        |  0.4.1.x-final
Component:  Core Tor/Tor                |        Version:
 Severity:  Normal                      |     Resolution:
 Keywords:  portability technical-debt  |  Actual Points:
Parent ID:                              |         Points:
 Reviewer:                              |        Sponsor:
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Comment (by rl1987):

 Replying to [ticket:29537 catalyst]:
 > Round-trip of `intptr_t` through `void *` isn't explicitly guaranteed by
 C99. There are implementation-defined behaviors for integer to `void *`,
 and vice versa. Only a round-trip of `void *` through `intptr_t` is
 guaranteed, not vice versa.

 Is that true though?

 From http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf:

 >7.18.1.4 Integer types capable of holding object pointers
 >1 The following type designates a signed integer type with the property
 that any valid
 >pointer to void can be converted to this type, then converted back to
 pointer to void,
 >and the result will compare equal to the original pointer:
 >intptr_t
 >The following type designates an unsigned integer type with the property
 that any valid
 >pointer to void can be converted to this type, then converted back to
 pointer to void,
 >and the result will compare equal to the original pointer:
 >uintptr_t
 >These types are optional.

 My reading of this is that it does guarantee the round-trip for all values
 between `INTPTR_MIN` and `INTPTR_MAX` provided that C implementation does
 have `intptr_t`. Or does C99 standard (which people are supposed to
 purchase from ISO) say differently?

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/29537#comment:5>
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