On Wed, 2013-09-11 at 21:08 +0930, Alan Modra wrote: > 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.
Hm, the libffi case is unfortunate. :( The alternative is to leave libffi alone, and require code that calls these interfaces with "bad" structs passed by value to be built using -mcompat-align-parm, which was provided for such compatibility issues. Hopefully there is a small number of cases where this can happen, and this could be documented with libffi and gcc. What do you think? Thanks, Bill > > 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. */ > >