Re: [PATCH, PowerPC] Fix PR57949 (ABI alignment issue)

[Alan Modra <amodra@gmail.com>]

On Wed, Aug 14, 2013 at 10:32:01AM -0500, Bill Schmidt wrote:
> This fixes a long-standing problem with GCC's implementation of the
> PPC64 ELF ABI.  If a structure contains a member requiring 128-bit
> alignment, and that structure is passed as a parameter, the parameter
> currently receives only 64-bit alignment.  This is an error, and is
> incompatible with correct code generated by the IBM XL compilers.

This caused multiple failures in the libffi testsuite:
libffi.call/cls_align_longdouble.c
libffi.call/cls_align_longdouble_split.c
libffi.call/cls_align_longdouble_split2.c
libffi.call/nested_struct5.c

Fixed by making the same alignment adjustment in libffi to structures
passed by value.  Bill, I think your patch needs to go on all active
gcc branches as otherwise we'll need different versions of libffi for
the next gcc releases.

The following was bootstrapped and regression checked powerpc64-linux.
OK for mainline, and the 4.7 and 4.8 branches when/if Bill's patch
goes in there?

	* src/powerpc/ffi.c (ffi_prep_args64): Align FFI_TYPE_STRUCT.
	(ffi_closure_helper_LINUX64): Likewise.

Index: libffi/src/powerpc/ffi.c
===================================================================
--- libffi/src/powerpc/ffi.c	(revision 202428)
+++ libffi/src/powerpc/ffi.c	(working copy)
@@ -462,6 +462,7 @@ ffi_prep_args64 (extended_cif *ecif, unsigned long
     double **d;
   } p_argv;
   unsigned long gprvalue;
+  unsigned long align;
 
   stacktop.c = (char *) stack + bytes;
   gpr_base.ul = stacktop.ul - ASM_NEEDS_REGISTERS64 - NUM_GPR_ARG_REGISTERS64;
@@ -532,6 +533,10 @@ ffi_prep_args64 (extended_cif *ecif, unsigned long
 #endif
 
 	case FFI_TYPE_STRUCT:
+	  align = (*ptr)->alignment;
+	  if (align > 16)
+	    align = 16;
+	  next_arg.ul = ALIGN (next_arg.ul, align);
 	  words = ((*ptr)->size + 7) / 8;
 	  if (next_arg.ul >= gpr_base.ul && next_arg.ul + words > gpr_end.ul)
 	    {
@@ -1349,6 +1354,7 @@ ffi_closure_helper_LINUX64 (ffi_closure *closure,
   long i, avn;
   ffi_cif *cif;
   ffi_dblfl *end_pfr = pfr + NUM_FPR_ARG_REGISTERS64;
+  unsigned long align;
 
   cif = closure->cif;
   avalue = alloca (cif->nargs * sizeof (void *));
@@ -1399,6 +1405,10 @@ ffi_closure_helper_LINUX64 (ffi_closure *closure,
 	  break;
 
 	case FFI_TYPE_STRUCT:
+	  align = arg_types[i]->alignment;
+	  if (align > 16)
+	    align = 16;
+	  pst = ALIGN (pst, align);
 #ifndef __LITTLE_ENDIAN__
 	  /* Structures with size less than eight bytes are passed
 	     left-padded.  */


-- 
Alan Modra
Australia Development Lab, IBM