This is an attempt to make GHC build reproducible. The name of .c files may end

up in the resulting binary (in the debug section), but not the directory.

Instead of using the process id, create a hash from the command line arguments,

and assume that is going to be unique.

Index: ghc-8.0.2/compiler/main/SysTools.hs

===================================================================

--- ghc-8.0.2.orig/compiler/main/SysTools.hs

+++ ghc-8.0.2/compiler/main/SysTools.hs

@@ -65,6 +65,7 @@

 import Util

 import DynFlags

 import Exception

+import Fingerprint

 import LlvmCodeGen.Base (llvmVersionStr, supportedLlvmVersion)

@@ -1145,8 +1146,8 @@

     mapping <- readIORef dir_ref

     case Map.lookup tmp_dir mapping of

         Nothing -> do

-            pid <- getProcessID

-            let prefix = tmp_dir  "ghc" ++ show pid ++ "_"

+            pid <- getStableProcessID

+            let prefix = tmp_dir  "ghc" ++ pid ++ "_"

             mask_ $ mkTempDir prefix

         Just dir -> return dir

   where

@@ -1562,6 +1563,13 @@

 getProcessID = System.Posix.Internals.c_getpid >>= return . fromIntegral

 #endif

+-- Debian-specific hack to get reproducible output, by not using the "random"

+-- pid, but rather something determinisic

+getStableProcessID :: IO String

+getStableProcessID = do

+    args <- getArgs

+    return $ take 4 $ show $ fingerprintString $ unwords args

+

 -- Divvy up text stream into lines, taking platform dependent

 -- line termination into account.

 linesPlatform :: String -> [String]