-- Best regards, LIU Hao From eeb30bf621baa3af1a73e84444e91bff297ef478 Mon Sep 17 00:00:00 2001 From: LIU Hao <lh_mo...@126.com> Date: Tue, 29 Apr 2025 10:43:06 +0800 Subject: [PATCH] i386/cygming: Decrease default preferred stack boundary for 32-bit targets This commit decreases the default preferred stack boundary to 4. In i386-options.cc, there's ix86_default_incoming_stack_boundary = PREFERRED_STACK_BOUNDARY; which sets the default incoming stack boundary to this value, if it's not overridden by other options or attributes. Previously, GCC preferred 16-byte alignment like other platforms, unless `-miamcu` was specified. However, the Microsoft x86 ABI only requires the stack be aligned to 4-byte boundaries. Callback functions from MSVC code may break this assumption by GCC (see reference below), causing local variables to be misaligned. For compatibility reasons, when the attribute `force_align_arg_pointer` is attached to a function, it continues to ensure the stack is at least aligned to a 16-byte boundary, as the documentation seems to suggest. After this change, `STACK_REALIGN_DEFAULT` no longer has an effect on this target, so it is removed. Reference: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111107#c9 Signed-off-by: LIU Hao <lh_mo...@126.com> gcc/ChangeLog: PR 111107 * config/i386/cygming.h (PREFERRED_STACK_BOUNDARY_DEFAULT): Override definition from i386.h. (STACK_REALIGN_DEFAULT): Undefine, as it no longer has an effect. * config/i386/i386.cc (ix86_update_stack_boundary): Force minimum 128-bit alignment if `force_align_arg_pointer`. Signed-off-by: LIU Hao <lh_mo...@126.com> --- gcc/config/i386/cygming.h | 9 ++++----- gcc/config/i386/i386.cc | 9 +++++++++ 2 files changed, 13 insertions(+), 5 deletions(-) diff --git a/gcc/config/i386/cygming.h b/gcc/config/i386/cygming.h index 3ddcbecb22fd..743cc38f5852 100644 --- a/gcc/config/i386/cygming.h +++ b/gcc/config/i386/cygming.h @@ -28,16 +28,15 @@ along with GCC; see the file COPYING3. If not see #undef TARGET_SEH #define TARGET_SEH (TARGET_64BIT_MS_ABI && flag_unwind_tables) +#undef PREFERRED_STACK_BOUNDARY_DEFAULT +#define PREFERRED_STACK_BOUNDARY_DEFAULT \ + (TARGET_64BIT ? 128 : MIN_STACK_BOUNDARY) + /* Win64 with SEH cannot represent DRAP stack frames. Disable its use. Force the use of different mechanisms to allocate aligned local data. */ #undef MAX_STACK_ALIGNMENT #define MAX_STACK_ALIGNMENT (TARGET_SEH ? 128 : MAX_OFILE_ALIGNMENT) -/* 32-bit Windows aligns the stack on a 4-byte boundary but SSE instructions - may require 16-byte alignment. */ -#undef STACK_REALIGN_DEFAULT -#define STACK_REALIGN_DEFAULT TARGET_SSE - /* Support hooks for SEH. */ #undef TARGET_ASM_UNWIND_EMIT #define TARGET_ASM_UNWIND_EMIT i386_pe_seh_unwind_emit diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc index 38df84f7db24..61e2acc53b7d 100644 --- a/gcc/config/i386/i386.cc +++ b/gcc/config/i386/i386.cc @@ -7920,6 +7920,15 @@ ix86_update_stack_boundary (void) if (ix86_tls_descriptor_calls_expanded_in_cfun && crtl->preferred_stack_boundary < 128) crtl->preferred_stack_boundary = 128; + + /* For 32-bit MS ABI, both the incoming and preferred stack boundaries + are 32 bits, but if force_align_arg_pointer is specified, it should + prefer 128 bits for a backward-compatibility reason, which is also + what the doc suggests. */ + if (lookup_attribute ("force_align_arg_pointer", + TYPE_ATTRIBUTES (TREE_TYPE (current_function_decl))) + && crtl->preferred_stack_boundary < 128) + crtl->preferred_stack_boundary = 128; } /* Handle the TARGET_GET_DRAP_RTX hook. Return NULL if no DRAP is -- 2.49.0
From eeb30bf621baa3af1a73e84444e91bff297ef478 Mon Sep 17 00:00:00 2001 From: LIU Hao <lh_mo...@126.com> Date: Tue, 29 Apr 2025 10:43:06 +0800 Subject: [PATCH] i386/cygming: Decrease default preferred stack boundary for 32-bit targets This commit decreases the default preferred stack boundary to 4. In i386-options.cc, there's ix86_default_incoming_stack_boundary = PREFERRED_STACK_BOUNDARY; which sets the default incoming stack boundary to this value, if it's not overridden by other options or attributes. Previously, GCC preferred 16-byte alignment like other platforms, unless `-miamcu` was specified. However, the Microsoft x86 ABI only requires the stack be aligned to 4-byte boundaries. Callback functions from MSVC code may break this assumption by GCC (see reference below), causing local variables to be misaligned. For compatibility reasons, when the attribute `force_align_arg_pointer` is attached to a function, it continues to ensure the stack is at least aligned to a 16-byte boundary, as the documentation seems to suggest. After this change, `STACK_REALIGN_DEFAULT` no longer has an effect on this target, so it is removed. Reference: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111107#c9 Signed-off-by: LIU Hao <lh_mo...@126.com> gcc/ChangeLog: PR 111107 * config/i386/cygming.h (PREFERRED_STACK_BOUNDARY_DEFAULT): Override definition from i386.h. (STACK_REALIGN_DEFAULT): Undefine, as it no longer has an effect. * config/i386/i386.cc (ix86_update_stack_boundary): Force minimum 128-bit alignment if `force_align_arg_pointer`. Signed-off-by: LIU Hao <lh_mo...@126.com> --- gcc/config/i386/cygming.h | 9 ++++----- gcc/config/i386/i386.cc | 9 +++++++++ 2 files changed, 13 insertions(+), 5 deletions(-) diff --git a/gcc/config/i386/cygming.h b/gcc/config/i386/cygming.h index 3ddcbecb22fd..743cc38f5852 100644 --- a/gcc/config/i386/cygming.h +++ b/gcc/config/i386/cygming.h @@ -28,16 +28,15 @@ along with GCC; see the file COPYING3. If not see #undef TARGET_SEH #define TARGET_SEH (TARGET_64BIT_MS_ABI && flag_unwind_tables) +#undef PREFERRED_STACK_BOUNDARY_DEFAULT +#define PREFERRED_STACK_BOUNDARY_DEFAULT \ + (TARGET_64BIT ? 128 : MIN_STACK_BOUNDARY) + /* Win64 with SEH cannot represent DRAP stack frames. Disable its use. Force the use of different mechanisms to allocate aligned local data. */ #undef MAX_STACK_ALIGNMENT #define MAX_STACK_ALIGNMENT (TARGET_SEH ? 128 : MAX_OFILE_ALIGNMENT) -/* 32-bit Windows aligns the stack on a 4-byte boundary but SSE instructions - may require 16-byte alignment. */ -#undef STACK_REALIGN_DEFAULT -#define STACK_REALIGN_DEFAULT TARGET_SSE - /* Support hooks for SEH. */ #undef TARGET_ASM_UNWIND_EMIT #define TARGET_ASM_UNWIND_EMIT i386_pe_seh_unwind_emit diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc index 38df84f7db24..61e2acc53b7d 100644 --- a/gcc/config/i386/i386.cc +++ b/gcc/config/i386/i386.cc @@ -7920,6 +7920,15 @@ ix86_update_stack_boundary (void) if (ix86_tls_descriptor_calls_expanded_in_cfun && crtl->preferred_stack_boundary < 128) crtl->preferred_stack_boundary = 128; + + /* For 32-bit MS ABI, both the incoming and preferred stack boundaries + are 32 bits, but if force_align_arg_pointer is specified, it should + prefer 128 bits for a backward-compatibility reason, which is also + what the doc suggests. */ + if (lookup_attribute ("force_align_arg_pointer", + TYPE_ATTRIBUTES (TREE_TYPE (current_function_decl))) + && crtl->preferred_stack_boundary < 128) + crtl->preferred_stack_boundary = 128; } /* Handle the TARGET_GET_DRAP_RTX hook. Return NULL if no DRAP is -- 2.49.0
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