Isn't mixing and matching and mismatching somewhat inevitable? Libffi & gcc
don't always come along with each other? One must never change the ABI?
- Jay
On Sep 11, 2013, at 5:55 AM, Bill Schmidt <wschm...@linux.vnet.ibm.com> wrote:
> 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. */
>
