Re: Incorrect data detected in the nested float struct with x86/libffi on Linux/64bit

[Anthony Green <green@moxielogic.com>]

Thank you, Jakub!  This has been committed.

AG

On Tue, Jun 15, 2021 at 3:02 PM Jakub Jelinek <jakub@redhat.com> wrote:

> On Tue, Jun 15, 2021 at 08:02:56PM +0200, Jakub Jelinek via Libffi-discuss
> wrote:
> > On Wed, Jun 09, 2021 at 12:50:08PM -0400, Anthony Green wrote:
> > > Thank you, Cheng.  Are you able to submit this test case as a github
> pull
> > > request?  The resulting CI testing will give us a broader picture of
> where
> > > we have problems.
> >
> > Comparing gcc/config/i386/ classify_argument and libffi
> classify_argument,
> > I found two important differences.
> >
> > The first one seems the most important one, even GCC 3.2 included the bit
> > offset (byte offset in libffi) in the calculation of number of words.
> > And the other change is https://gcc.gnu.org/PR38781.
> >
> > With this patch the posted testcase works and the testsuite on
> x86_64-linux
> > still passes, but haven't done more testing than that.
> >
> > Haven't tried yet to adapt one of the
> > libffi/testsuite/libffi.call/nested_struct*.c tests to cover this though.
>
> And here is one with a testcase (modified nested_struct2.c for it).
>
> I'm unsure about the current relationship between the github and gcc
> copy of libffi, shall it go to both, or just one of them and be
> cherry-picked from there?
>
> Tested on x86_64-linux.
>
> 2021-06-15  Jakub Jelinek  <jakub@redhat.com>
>
>         * src/x86/ffi64.c (classify_argument): For FFI_TYPE_STRUCT set
> words
>         to number of words needed for type->size + byte_offset bytes rather
>         than just type->size bytes.  Compute pos before the loop and check
>         total size of the structure.
>         * testsuite/libffi.call/nested_struct12.c: New test.
>
> --- libffi/src/x86/ffi64.c.jj   2020-01-14 20:02:48.557583260 +0100
> +++ libffi/src/x86/ffi64.c      2021-06-15 19:50:06.059108230 +0200
> @@ -217,7 +217,8 @@ classify_argument (ffi_type *type, enum
>      case FFI_TYPE_STRUCT:
>        {
>         const size_t UNITS_PER_WORD = 8;
> -       size_t words = (type->size + UNITS_PER_WORD - 1) / UNITS_PER_WORD;
> +       size_t words = (type->size + byte_offset + UNITS_PER_WORD - 1)
> +                      / UNITS_PER_WORD;
>         ffi_type **ptr;
>         int i;
>         enum x86_64_reg_class subclasses[MAX_CLASSES];
> @@ -241,16 +242,16 @@ classify_argument (ffi_type *type, enum
>         /* Merge the fields of structure.  */
>         for (ptr = type->elements; *ptr != NULL; ptr++)
>           {
> -           size_t num;
> +           size_t num, pos;
>
>             byte_offset = ALIGN (byte_offset, (*ptr)->alignment);
>
>             num = classify_argument (*ptr, subclasses, byte_offset % 8);
>             if (num == 0)
>               return 0;
> -           for (i = 0; i < num; i++)
> +           pos = byte_offset / 8;
> +           for (i = 0; i < num && (i + pos) < words; i++)
>               {
> -               size_t pos = byte_offset / 8;
>                 classes[i + pos] =
>                   merge_classes (subclasses[i], classes[i + pos]);
>               }
> --- libffi/testsuite/libffi.call/nested_struct12.c.jj   2021-06-15
> 20:31:43.327144303 +0200
> +++ libffi/testsuite/libffi.call/nested_struct12.c      2021-06-15
> 20:47:13.129489263 +0200
> @@ -0,0 +1,107 @@
> +/* Area:       ffi_call, closure_call
> +   Purpose:    Check structure passing.
> +   Limitations:        none.
> +   PR:         none.
> +   Originator: <jincheng@ca.ibm.com> and <jakub@redhat.com> 20210609
> */
> +
> +/* { dg-do run } */
> +#include "ffitest.h"
> +
> +typedef struct A {
> +  float a, b;
> +} A;
> +
> +typedef struct B {
> +  float x;
> +  struct A y;
> +} B;
> +
> +B B_fn(float b0, struct B b1)
> +{
> +  struct B result;
> +
> +  result.x = b0 + b1.x;
> +  result.y.a = b0 + b1.y.a;
> +  result.y.b = b0 + b1.y.b;
> +
> +  printf("%g %g %g %g: %g %g %g\n", b0, b1.x, b1.y.a, b1.y.b,
> +        result.x, result.y.a, result.y.b);
> +
> +  return result;
> +}
> +
> +static void
> +B_gn(ffi_cif* cif __UNUSED__, void* resp, void** args,
> +     void* userdata __UNUSED__)
> +{
> +  float b0;
> +  struct B b1;
> +
> +  b0 = *(float*)(args[0]);
> +  b1 = *(struct B*)(args[1]);
> +
> +  *(B*)resp = B_fn(b0, b1);
> +}
> +
> +int main (void)
> +{
> +  ffi_cif cif;
> +  void *code;
> +  ffi_closure *pcl = ffi_closure_alloc(sizeof(ffi_closure), &code);
> +  void* args_dbl[3];
> +  ffi_type* cls_struct_fields[3];
> +  ffi_type* cls_struct_fields1[3];
> +  ffi_type cls_struct_type, cls_struct_type1;
> +  ffi_type* dbl_arg_types[3];
> +
> +  float e_dbl = 12.125f;
> +  struct B f_dbl = { 24.75f, { 31.625f, 32.25f } };
> +
> +  struct B res_dbl;
> +
> +  cls_struct_type.size = 0;
> +  cls_struct_type.alignment = 0;
> +  cls_struct_type.type = FFI_TYPE_STRUCT;
> +  cls_struct_type.elements = cls_struct_fields;
> +
> +  cls_struct_type1.size = 0;
> +  cls_struct_type1.alignment = 0;
> +  cls_struct_type1.type = FFI_TYPE_STRUCT;
> +  cls_struct_type1.elements = cls_struct_fields1;
> +
> +  cls_struct_fields[0] = &ffi_type_float;
> +  cls_struct_fields[1] = &ffi_type_float;
> +  cls_struct_fields[2] = NULL;
> +
> +  cls_struct_fields1[0] = &ffi_type_float;
> +  cls_struct_fields1[1] = &cls_struct_type;
> +  cls_struct_fields1[2] = NULL;
> +
> +
> +  dbl_arg_types[0] = &ffi_type_float;
> +  dbl_arg_types[1] = &cls_struct_type1;
> +  dbl_arg_types[2] = NULL;
> +
> +  CHECK(ffi_prep_cif(&cif, FFI_DEFAULT_ABI, 2, &cls_struct_type1,
> +                    dbl_arg_types) == FFI_OK);
> +
> +  args_dbl[0] = &e_dbl;
> +  args_dbl[1] = &f_dbl;
> +  args_dbl[2] = NULL;
> +
> +  ffi_call(&cif, FFI_FN(B_fn), &res_dbl, args_dbl);
> +  /* { dg-output "12.125 24.75 31.625 32.25: 36.875 43.75 44.375" } */
> +  CHECK( res_dbl.x == (e_dbl + f_dbl.x));
> +  CHECK( res_dbl.y.a == (e_dbl + f_dbl.y.a));
> +  CHECK( res_dbl.y.b == (e_dbl + f_dbl.y.b));
> +
> +  CHECK(ffi_prep_closure_loc(pcl, &cif, B_gn, NULL, code) == FFI_OK);
> +
> +  res_dbl = ((B(*)(float, B))(code))(e_dbl, f_dbl);
> +  /* { dg-output "\n12.125 24.75 31.625 32.25: 36.875 43.75 44.375" } */
> +  CHECK( res_dbl.x == (e_dbl + f_dbl.x));
> +  CHECK( res_dbl.y.a == (e_dbl + f_dbl.y.a));
> +  CHECK( res_dbl.y.b == (e_dbl + f_dbl.y.b));
> +
> +  exit(0);
> +}
>
>
>         Jakub
>
>