Hello, Jonathan,
On May 9, 2020, Jonathan Wakely <jwak...@redhat.com> wrote:
> On 08/05/20 17:22 -0300, Alexandre Oliva wrote:
>> (Couldn't r1->allocate(2, alignof(char)) possibly return a pointer
>> that's *not* aligned<max_align_t>? Maybe we should drop the test even
>> if !defined(BAD_MAX_ALIGN_T).)
> Yes.
> Different malloc implementations interpret the C standard differently
> here. One interpretation is that all allocations must be aligned to
> alignof(max_align_t) but another is that allocations smaller than that
> don't need to meet that requirement. An object that is two bytes in
> size cannot require 16-byte alignment (otherwise its sizeof would be
> 16 too).
I understand you're talking about malloc because that's what our
implementation ultimately uses, but my question was on language
lawyering, on whether C++ would mandate more alignment than requested by
the caller of allocate. If it were to do so, I wonder what the point of
specifying the alignment explicitly would be.
> Please do remove that line of the test, instead of wrapping it in the
> #ifdef.
> OK for master.
Thanks, here's what I'm installing in master.
x86-vxworks malloc aligns to 8 bytes like solaris
From: Alexandre Oliva <ol...@adacore.com>
Vxworks 7's malloc, like Solaris', only ensures 8-byte alignment of
returned pointers on 32-bit x86, though GCC's stddef.h defines
max_align_t with 16-byte alignment for __float128. This patch enables
on x86-vxworks the same memory_resource workaround used for x86-solaris.
The testsuite also had a workaround, defining BAD_MAX_ALIGN_T and
xfailing the test; extend those to x86-vxworks as well, and remove the
check for char-aligned requested allocation to be aligned like
max_align_t. With that change, the test passes on x86-vxworks; I'm
guessing that's the same reason for the test not to pass on
x86-solaris (and on x86_64-solaris -m32), so with the fix, I'm
tentatively removing the xfail.
for libstdc++-v3/ChangeLog
PR libstdc++/77691
* include/experimental/memory_resource
(__resource_adaptor_imp::do_allocate): Handle max_align_t on
x86-vxworks as on x86-solaris.
(__resource_adaptor_imp::do_deallocate): Likewise.
* testsuite/experimental/memory_resource/new_delete_resource.cc:
Drop xfail.
(BAD_MAX_ALIGN_T): Define on x86-vxworks as on x86-solaris.
(test03): Drop max-align test for char-aligned alloc.
---
libstdc++-v3/include/experimental/memory_resource | 4 ++--
.../memory_resource/new_delete_resource.cc | 4 +---
2 files changed, 3 insertions(+), 5 deletions(-)
diff --git a/libstdc++-v3/include/experimental/memory_resource
b/libstdc++-v3/include/experimental/memory_resource
index 850a78d..1c4de70 100644
--- a/libstdc++-v3/include/experimental/memory_resource
+++ b/libstdc++-v3/include/experimental/memory_resource
@@ -413,7 +413,7 @@ namespace pmr {
do_allocate(size_t __bytes, size_t __alignment) override
{
// Cannot use max_align_t on 32-bit Solaris x86, see PR libstdc++/77691
-#if ! (defined __sun__ && defined __i386__)
+#if ! ((defined __sun__ || defined __VXWORKS__) && defined __i386__)
if (__alignment == alignof(max_align_t))
return _M_allocate<alignof(max_align_t)>(__bytes);
#endif
@@ -439,7 +439,7 @@ namespace pmr {
do_deallocate(void* __ptr, size_t __bytes, size_t __alignment) noexcept
override
{
-#if ! (defined __sun__ && defined __i386__)
+#if ! ((defined __sun__ || defined __VXWORKS__) && defined __i386__)
if (__alignment == alignof(max_align_t))
return (void) _M_deallocate<alignof(max_align_t)>(__ptr, __bytes);
#endif
diff --git
a/libstdc++-v3/testsuite/experimental/memory_resource/new_delete_resource.cc
b/libstdc++-v3/testsuite/experimental/memory_resource/new_delete_resource.cc
index 8a98954..65a42da 100644
--- a/libstdc++-v3/testsuite/experimental/memory_resource/new_delete_resource.cc
+++ b/libstdc++-v3/testsuite/experimental/memory_resource/new_delete_resource.cc
@@ -17,13 +17,12 @@
// { dg-do run { target c++14 } }
// { dg-require-cstdint "" }
-// { dg-xfail-run-if "PR libstdc++/77691" { { i?86-*-solaris2.*
x86_64-*-solaris2.* } && ilp32 } }
#include <experimental/memory_resource>
#include <cstdlib>
#include <testsuite_hooks.h>
-#if defined __sun__ && defined __i386__
+#if (defined __sun__ || defined __VXWORKS__) && defined __i386__
// See PR libstdc++/77691
# define BAD_MAX_ALIGN_T 1
#endif
@@ -128,7 +127,6 @@ test03()
p = r1->allocate(2, alignof(char));
VERIFY( bytes_allocated == 2 );
- VERIFY( aligned<max_align_t>(p) );
r1->deallocate(p, 2, alignof(char));
VERIFY( bytes_allocated == 0 );
--
Alexandre Oliva, freedom fighter he/him https://FSFLA.org/blogs/lxo/
Free Software Evangelist Stallman was right, but he's left :(
GNU Toolchain Engineer Live long and free, and prosper ethically
