diff options
| -rw-r--r-- | includes/Stg.h | 30 |
1 files changed, 29 insertions, 1 deletions
diff --git a/includes/Stg.h b/includes/Stg.h index 1707c9b9a4..9edb6a0f2b 100644 --- a/includes/Stg.h +++ b/includes/Stg.h @@ -213,7 +213,35 @@ 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() +#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 |