Hi HJ,
I am trying to track down a misalignment of the stack on Darwin (pr78444).
In r163971 you applied this:
--- gcc/config/i386/darwin.h (revision 163970)
+++ gcc/config/i386/darwin.h (revision 163971)
@@ -79,7 +79,9 @@
Failure to ensure this will lead to a crash in the system libraries
or dynamic loader. */
#undef STACK_BOUNDARY
-#define STACK_BOUNDARY 128
+#define STACK_BOUNDARY \
+ ((profile_flag || (TARGET_64BIT && ix86_abi == MS_ABI)) \
+ ? 128 : BITS_PER_WORD)
#undef MAIN_STACK_BOUNDARY
#define MAIN_STACK_BOUNDARY 128
@@ -91,7 +93,7 @@
it's below the minimum. */
#undef PREFERRED_STACK_BOUNDARY
#define PREFERRED_STACK_BOUNDARY \
- MAX (STACK_BOUNDARY, ix86_preferred_stack_boundary)
+ MAX (128, ix86_preferred_stack_boundary
===
I realise it’s a long time ago …
.. but, have you any pointer to the reasoning here or what problem was being
solved?
(perhaps mail list discussion?)
===
Darwin’s 32b ABI mandates 128b alignment at functions calls:
"The function calling conventions used in the IA-32 environment are the same
as those used in the System V IA-32 ABI, with the following exceptions:
■ Different rules for returning structures
■ The stack is 16-byte aligned at the point of function calls
“
Darwin’s 64b ABI refers directly to the SysV document, which also mandates
[section 3.2.2] 128b (or 256b when __m256 is passed).
===
The following patch resolves pr78444 - but it’s not clear if it’s a correct fix
- or we should be looking for an alternate solution to whatever r193671 was
intending to achieve.
thanks,
Iain
[PATCH] Fix for PR78444.
maybe.
---
gcc/config/i386/i386.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index 163682bdff..405bfd082b 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -11530,6 +11530,15 @@ ix86_compute_frame_layout (void)
crtl->preferred_stack_boundary = 128;
crtl->stack_alignment_needed = 128;
}
+ else if (TARGET_MACHO && crtl->preferred_stack_boundary < 128
+ && !crtl->is_leaf)
+ {
+ /* Darwin's ABI specifies 128b alignment for both 32 and
+ 64 bit variants at call sites. So we apply this if the
+ current function is not a leaf. */
+ crtl->preferred_stack_boundary = 128;
+ crtl->stack_alignment_needed = 128;
+ }
stack_alignment_needed = crtl->stack_alignment_needed / BITS_PER_UNIT;
preferred_alignment = crtl->preferred_stack_boundary / BITS_PER_UNIT;
--
2.17.1
