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Fixed bpo-29565: Corrected ctypes passing of large structs by value on Windows AMD64. (#168)

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* Fixed bpo-29565: Corrected ctypes passing of large structs by value.

Added code and test to check that when a structure passed by value
is large enough to need to be passed by reference, a copy of the
original structure is passed. The callee updates the passed-in value,
and the test verifies that the caller's copy is unchanged. A similar
change was also added to the test added for bpo-20160 (that test was
passing, but the changes should guard against regressions).

* Reverted unintended whitespace changes.
This commit is contained in:
Vinay Sajip 2017-02-20 00:16:33 +00:00 • committed by GitHub
parent 3eea8c67fa
commit a86339b83f
4 changed files with 57 additions and 0 deletions
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13
Modules/_ctypes/_ctypes_test.c
View file

@ -44,6 +44,19 @@ _testfunc_cbk_large_struct(Test in, void (*func)(Test))
func(in);
}
/*
* See issue 29565. Update a structure passed by value;
* the caller should not see any change.
*/
EXPORT(void)
_testfunc_large_struct_update_value(Test in)
{
in.first = 0x0badf00d;
in.second = 0x0badf00d;
in.third = 0x0badf00d;
}
EXPORT(void)testfunc_array(int values[4])
{
printf("testfunc_array %d %d %d %d\n",

10
Modules/_ctypes/libffi_msvc/ffi.c
View file

@ -239,6 +239,16 @@ ffi_call(/*@dependent@*/ ffi_cif *cif,
break;
#else
case FFI_SYSV:
/* If a single argument takes more than 8 bytes,
then a copy is passed by reference. */
for (unsigned i = 0; i < cif->nargs; i++) {
size_t z = cif->arg_types[i]->size;
if (z > 8) {
void *temp = alloca(z);
memcpy(temp, avalue[i], z);
avalue[i] = temp;
}
}
/*@-usedef@*/
return ffi_call_AMD64(ffi_prep_args, &ecif, cif->bytes,
cif->flags, ecif.rvalue, fn);