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authorMarek Polacek <polacek@redhat.com>2020-03-05 14:07:25 -0500
committerMarek Polacek <polacek@redhat.com>2020-03-09 09:24:55 -0400
commit8475f2902a2e2ca5f7ace8bc5265bd1a815dda20 (patch)
tree616f67587661f17ab966cc152b5fd8cd25917fb0
parent157e23d8803dda38d7d38404bcc4284ce2dce3b5 (diff)
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c++: Fix ABI issue with alignas on armv7hl [PR94050]
The static_assert in the following test was failing on armv7hl because we were disregarding the alignas specifier on Cell. BaseShape's data takes up 20B on 32-bit architectures, but we failed to round up its TYPE_SIZE. This happens since the <https://gcc.gnu.org/ml/gcc-patches/2019-06/msg01189.html> patch: here, in layout_class_type for TenuredCell, we see that the size of TenuredCell and its CLASSTYPE_AS_BASE match, so we set CLASSTYPE_AS_BASE (t) = t; While TYPE_USER_ALIGN of TenuredCell was 0, because finalize_type_size called from finish_record_layout reset it, TYPE_USER_ALIGN of its CLASSTYPE_AS_BASE still remained 1. After we replace it, it's no longer 1. Then we perform layout_empty_base_or_field for TenuredCell and since TYPE_USER_ALIGN of its CLASSTYPE_AS_BASE is now 0, we don't do this adjustment: if (CLASSTYPE_USER_ALIGN (type)) { rli->record_align = MAX (rli->record_align, CLASSTYPE_ALIGN (type)); if (warn_packed) rli->unpacked_align = MAX (rli->unpacked_align, CLASSTYPE_ALIGN (type)); TYPE_USER_ALIGN (rli->t) = 1; } where rli->t is BaseShape. Then finalize_record_size won't use the correct rli->record_align and therefore /* Round the size up to be a multiple of the required alignment. */ TYPE_SIZE (rli->t) = round_up (unpadded_size, TYPE_ALIGN (rli->t)); after this we end up with the wrong size. Since the original fix was to avoid creating extra copies for LTO purposes, I think the following fix should be acceptable. PR c++/94050 - ABI issue with alignas on armv7hl. * class.c (layout_class_type): Don't replace a class's CLASSTYPE_AS_BASE if their TYPE_USER_ALIGN don't match. * g++.dg/abi/align3.C: New test.
-rw-r--r--gcc/cp/ChangeLog6
-rw-r--r--gcc/cp/class.c4
-rw-r--r--gcc/testsuite/ChangeLog5
-rw-r--r--gcc/testsuite/g++.dg/abi/align3.C12
4 files changed, 27 insertions, 0 deletions
diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 128880b..5fc3e7d 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,9 @@
+2020-03-09 Marek Polacek <polacek@redhat.com>
+
+ PR c++/94050 - ABI issue with alignas on armv7hl.
+ * class.c (layout_class_type): Don't replace a class's
+ CLASSTYPE_AS_BASE if their TYPE_USER_ALIGN don't match.
+
2020-03-09 Bin Cheng <bin.cheng@linux.alibaba.com>
* coroutines.cc (build_actor_fn): Factor out code inserting the
diff --git a/gcc/cp/class.c b/gcc/cp/class.c
index b3787f7..5340799 100644
--- a/gcc/cp/class.c
+++ b/gcc/cp/class.c
@@ -6705,6 +6705,10 @@ layout_class_type (tree t, tree *virtuals_p)
/* If we didn't end up needing an as-base type, don't use it. */
if (CLASSTYPE_AS_BASE (t) != t
+ /* If T's CLASSTYPE_AS_BASE is TYPE_USER_ALIGN, but T is not,
+ replacing the as-base type would change CLASSTYPE_USER_ALIGN,
+ causing us to lose the user-specified alignment as in PR94050. */
+ && TYPE_USER_ALIGN (t) == TYPE_USER_ALIGN (CLASSTYPE_AS_BASE (t))
&& tree_int_cst_equal (TYPE_SIZE (t),
TYPE_SIZE (CLASSTYPE_AS_BASE (t))))
CLASSTYPE_AS_BASE (t) = t;
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index d8719a4..6c0fab6 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2020-03-09 Marek Polacek <polacek@redhat.com>
+
+ PR c++/94050 - ABI issue with alignas on armv7hl.
+ * g++.dg/abi/align3.C: New test.
+
2020-03-09 Christophe Lyon <christophe.lyon@linaro.org>
* gcc.target/arm/fuse-caller-save.c: Fix DejaGnu typo.
diff --git a/gcc/testsuite/g++.dg/abi/align3.C b/gcc/testsuite/g++.dg/abi/align3.C
new file mode 100644
index 0000000..a56693a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/abi/align3.C
@@ -0,0 +1,12 @@
+// PR c++/94050 - ABI issue with alignas on armv7hl.
+// { dg-do compile { target c++11 } }
+
+struct alignas(8) Cell {};
+struct TenuredCell : public Cell {};
+struct BaseShape : public TenuredCell {
+ void *p;
+ unsigned q, r;
+ void *s;
+ __UINTPTR_TYPE__ t;
+};
+static_assert (sizeof (BaseShape) % 8 == 0, "");