Re: [commit: ghc] master: Be less untruthful about the prototypes of external functions (5a31f23)

23 Apr 2014

Could we have a comment with the ticket number next to the prototype 
please?  Otherwise some well-meaning developer will "fix" it again in 
the future :-)

Cheers,
Simon

On 22/04/2014 05:40, git@git.haskell.org wrote:
...
Repository : ssh://git@git.haskell.org/ghc
On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/5a31f231eebfb8140f9b519b166094d9d4...
...
---------------------------------------------------------------
commit 5a31f231eebfb8140f9b519b166094d9d4fc2d79
Author: Colin Watson 
Date:   Sat Apr 12 01:55:07 2014 +0100
Be less untruthful about the prototypes of external functions
GHC's generated C code uses dummy prototypes for foreign imports.  At the
     moment these all claim to be (void), i.e. functions of zero arguments.  On
     most platforms this doesn't matter very much: calls to these functions put
     the parameters in the usual places anyway, and (with the exception of
     varargs) things just work.
However, the ELFv2 ABI on ppc64 optimises stack allocation
     (http://gcc.gnu.org/ml/gcc-patches/2013-11/msg01149.html): a call to a
     function that has a prototype, is not varargs, and receives all parameters
     in registers rather than on the stack does not require the caller to
     allocate an argument save area.  The incorrect prototypes cause GCC to
     believe that all functions declared this way can be called without an
     argument save area, but if the callee has sufficiently many arguments then
     it will expect that area to be present, and will thus corrupt the caller's
     stack.  This happens in particular with calls to runInteractiveProcess in
     libraries/process/cbits/runProcess.c.
The simplest fix appears to be to declare these external functions with an
     unspecified argument list rather than a void argument list.  This is no
     worse for platforms that don't care either way, and allows a successful
     bootstrap of GHC 7.8 on little-endian Linux ppc64 (which uses the ELFv2
     ABI).
Fixes #8965
Signed-off-by: Colin Watson 
     Signed-off-by: Austin Seipp 
...
---------------------------------------------------------------
5a31f231eebfb8140f9b519b166094d9d4fc2d79
  includes/Stg.h |    2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/includes/Stg.h b/includes/Stg.h
index be966aa..1707c9b 100644
--- a/includes/Stg.h
+++ b/includes/Stg.h
@@ -213,7 +213,7 @@ typedef StgFunPtr       F_;
  #define II_(X)          static StgWordArray (X) GNU_ATTRIBUTE(aligned (8))
  #define IF_(f)    static StgFunPtr GNUC3_ATTRIBUTE(used) f(void)
  #define FN_(f)    StgFunPtr f(void)
-#define EF_(f)    extern StgFunPtr f(void)
+#define EF_(f)    extern StgFunPtr f()
/* -----------------------------------------------------------------------------
     Tail calls
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Re: [commit: ghc] master: Be less untruthful about the prototypes of external functions (5a31f23)

Simon Marlow