Commit 31a7bb46 authored by Simon Peyton Jones's avatar Simon Peyton Jones
Browse files

Add comments to explain the change to EF_ (Trac #8965)

parent 0a0115fe
...@@ -213,7 +213,35 @@ typedef StgFunPtr F_; ...@@ -213,7 +213,35 @@ typedef StgFunPtr F_;
#define II_(X) static StgWordArray (X) GNU_ATTRIBUTE(aligned (8)) #define II_(X) static StgWordArray (X) GNU_ATTRIBUTE(aligned (8))
#define IF_(f) static StgFunPtr GNUC3_ATTRIBUTE(used) f(void) #define IF_(f) static StgFunPtr GNUC3_ATTRIBUTE(used) f(void)
#define FN_(f) StgFunPtr f(void) #define FN_(f) StgFunPtr f(void)
#define EF_(f) extern StgFunPtr f() #define EF_(f) extern StgFunPtr f() /* See Note [External function prototypes] */
/* Note [External function prototypes] See Trac #8965
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The external-function macro EF_(F) used to be defined as
extern StgFunPtr f(void)
i.e a function 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, and led to Trac #8965.
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).
*/
/* ----------------------------------------------------------------------------- /* -----------------------------------------------------------------------------
Tail calls Tail calls
......
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