[GHC] #9351: add ability to version symbols .c for packages with C code

[GHC]

#9351: add ability to version symbols .c for packages with C code
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       Reporter:  slyfox             |                   Owner:
           Type:  feature request    |                  Status:  new
       Priority:  normal             |               Milestone:
      Component:  Compiler           |                 Version:  7.8.3
       Keywords:  backpack           |        Operating System:
   Architecture:  Unknown/Multiple   |  Unknown/Multiple
     Difficulty:  Unknown            |         Type of failure:
     Blocked By:                     |  None/Unknown
Related Tickets:                     |               Test Case:
                                     |                Blocking:
                                     |  Differential Revisions:
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 Let's consider an example:

 We have a haskell package with some C code imported in
 haskell:
 {{{
 // a.h file
 int get_something(void);

 // a.c file
 #include "a.h"
 int get_something(void) { return 42; }

 // M.hs file
 module M where

 foreign import ccall "a.h get_something" :: IO Int
 }}}

 The problem here is we can't mix that package with other
 packages having global 'get_something' symbol.

 Sometimes it happens when a package copies part of
 implementation from another package with .c bits under different
 haskell namespace. Haskell parts would coexist freely, but
 not C symbols.

 Would be great if ghc would export some unique
 package identifier in a way C code could attach
 it to all exported symbols making linking possible.

 Something like that:
 {{{
 // a.h file
 #include "HsFFI.h" /* #define FOR_HASKELL(__sym) package_id_##__sym */
 int FOR_HASKELL(get_something)(void);

 // a.c file
 #include "a.h"
 int FOR_HASKELL(get_something)(void) { return 42; }

 // M.hs file
 module M where

 foreign import ccall-for-haskell "a.h get_something" :: IO Int
 }}}

 That way we explicitly mark symbol as inaccessible to
 external plain C code.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9351>
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