[commit: ghc] ghc-7.8: driver: pass '-fPIC' option to assembler as well (39d0cad)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : ghc-7.8
Link       : http://ghc.haskell.org/trac/ghc/changeset/39d0cad37a91591ae5be22200753206b57d0f169/ghc

>---------------------------------------------------------------

commit 39d0cad37a91591ae5be22200753206b57d0f169
Author: Sergei Trofimovich <slyfox at gentoo.org>
Date:   Wed Aug 27 22:19:52 2014 +0300

    driver: pass '-fPIC' option to assembler as well
    
    Summary:
    Before the patch '-fPIC' was passed only to C compiler,
    but not to assembler itself.
    
    It led to runtime crash in GHC_DYNAMIC_PROGRAMS=YES mode
    on sparc32.
    
    Technical details are in 'Note [-fPIC for assembler]'.
    
    Signed-off-by: Sergei Trofimovich <slyfox at gentoo.org>
    
    Test Plan: validate on sparc
    
    Reviewers: simonmar, austin, kgardas
    
    Reviewed By: austin
    
    Subscribers: simonmar, ezyang, carter
    
    Differential Revision: https://phabricator.haskell.org/D177
    
    (cherry picked from commit a93ab43ab5f40cadbedea2f6342b93c245e91434)


>---------------------------------------------------------------

39d0cad37a91591ae5be22200753206b57d0f169
 compiler/main/DriverPipeline.hs | 44 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/compiler/main/DriverPipeline.hs b/compiler/main/DriverPipeline.hs
index d2d2bc0..745199e 100644
--- a/compiler/main/DriverPipeline.hs
+++ b/compiler/main/DriverPipeline.hs
@@ -1208,6 +1208,7 @@ runPhase (RealPhase (As with_cpp)) input_fn dflags
 
         as_prog <- whichAsProg
         let cmdline_include_paths = includePaths dflags
+        let pic_c_flags = picCCOpts dflags
 
         next_phase <- maybeMergeStub
         output_fn <- phaseOutputFilename next_phase
@@ -1221,6 +1222,9 @@ runPhase (RealPhase (As with_cpp)) input_fn dflags
                 = liftIO $ as_prog dflags
                        ([ SysTools.Option ("-I" ++ p) | p <- cmdline_include_paths ]
 
+                       -- See Note [-fPIC for assembler]
+                       ++ map SysTools.Option pic_c_flags
+
         -- We only support SparcV9 and better because V8 lacks an atomic CAS
         -- instruction so we have to make sure that the assembler accepts the
         -- instruction set. Note that the user can still override this
@@ -1262,6 +1266,8 @@ runPhase (RealPhase SplitAs) _input_fn dflags
             osuf = objectSuf dflags
             split_odir  = base_o ++ "_" ++ osuf ++ "_split"
 
+        let pic_c_flags = picCCOpts dflags
+
         -- this also creates the hierarchy
         liftIO $ createDirectoryIfMissing True split_odir
 
@@ -1295,6 +1301,9 @@ runPhase (RealPhase SplitAs) _input_fn dflags
                            then [SysTools.Option "-mcpu=v9"]
                            else []) ++
 
+                          -- See Note [-fPIC for assembler]
+                          map SysTools.Option pic_c_flags ++
+
                           [ SysTools.Option "-c"
                           , SysTools.Option "-o"
                           , SysTools.FileOption "" (split_obj n)
@@ -2210,3 +2219,38 @@ haveRtsOptsFlags dflags =
          isJust (rtsOpts dflags) || case rtsOptsEnabled dflags of
                                         RtsOptsSafeOnly -> False
                                         _ -> True
+
+-- Note [-fPIC for assembler]
+-- When compiling .c source file GHC's driver pipeline basically
+-- does the following two things:
+--   1. ${CC}              -S 'PIC_CFLAGS' source.c
+--   2. ${CC} -x assembler -c 'PIC_CFLAGS' source.S
+--
+-- Why do we need to pass 'PIC_CFLAGS' both to C compiler and assembler?
+-- Because on some architectures (at least sparc32) assembler also choses
+-- relocation type!
+-- Consider the following C module:
+--
+--     /* pic-sample.c */
+--     int v;
+--     void set_v (int n) { v = n; }
+--     int  get_v (void)  { return v; }
+--
+--     $ gcc -S -fPIC pic-sample.c
+--     $ gcc -c       pic-sample.s -o pic-sample.no-pic.o # incorrect binary
+--     $ gcc -c -fPIC pic-sample.s -o pic-sample.pic.o    # correct binary
+--
+--     $ objdump -r -d pic-sample.pic.o    > pic-sample.pic.o.od
+--     $ objdump -r -d pic-sample.no-pic.o > pic-sample.no-pic.o.od
+--     $ diff -u pic-sample.pic.o.od pic-sample.no-pic.o.od
+--
+-- Most of architectures won't show any difference in this test, but on sparc32
+-- the following assembly snippet:
+--
+--    sethi   %hi(_GLOBAL_OFFSET_TABLE_-8), %l7
+--
+-- generates two kinds or relocations, only 'R_SPARC_PC22' is correct:
+--
+--       3c:  2f 00 00 00     sethi  %hi(0), %l7
+--    -                       3c: R_SPARC_PC22        _GLOBAL_OFFSET_TABLE_-0x8
+--    +                       3c: R_SPARC_HI22        _GLOBAL_OFFSET_TABLE_-0x8