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help / color / mirror / Atom feedFrom: Greg Burd <[email protected]>
To: PostgreSQL Hackers <[email protected]>
Subject: Re: Trying out <stdatomic.h>
Date: Sun, 23 Nov 2025 10:22:47 -0500
Message-ID: <[email protected]> (raw)
In-Reply-To: <CA+hUKGKFvu3zyvv3aaj5hHs9VtWcjFAmisOwOc7aOZNc5AF3NA@mail.gmail.com>
References: <CA+hUKGKFvu3zyvv3aaj5hHs9VtWcjFAmisOwOc7aOZNc5AF3NA@mail.gmail.com>
On Mon, Nov 10, 2025, at 8:17 AM, Thomas Munro wrote:
> Hi,
>
> Here is an experimental patch to try out standard C (and C++) atomics
> to implement port/atomics.h, and also add more types and operations.
> It's mostly just redirecting our names to the standard ones, except
> for our barriers and slightly extended pg_atomic_flag, so there isn't
> much left of the code.
>
> Here also is a semi-independent patch to implement storage/spin.h with
> pg_atomic_flag. It keeps a small amount of the architecture-specific
> magic, but moves it out to src/port/spin_delay.h.
>
> I'm not saying they're correct, performant or portable yet, that'll
> require studying codegen and performance on a bunch of weird and
> wonderful systems, but they at least passes basic testing on the usual
> suspects and CI systems, except for Windows which needs a newer
> toolchain so I haven't tried yet. It should hopefully just work⢠on
> VS 2022 (same version that provides <threads.h>, about which more
> soon).
>
> All that being the case, it's not far enough along to be a serious
> proposal, but I imagine others will be looking into things like this
> since we pulled the trigger on C11 and I figured I might as well share
> a basic working patch set to avoid duplicated effort... Hopefully it
> works well enough to kick the tyres and try to find the difficult
> problems, test it out on weird systems, etc etc.
>
> Attachments:
> * v1-0001-Add-some-missing-include-limits.h.patch
> * v1-0002-Redefine-port-atomics.h-on-top-of-stdatomic.h.patch
> * v1-0003-Use-atomics-API-to-implement-spinlocks.patch
> * v1-0004-Remove-configure-meson-checks-for-atomics.patch
Hello Thomas,
First off, thanks for working on this set of changes. I like your changes in general, except for removing Solaris/Illumos (but I get it). ;-P
As mentioned on a separate thread about fixing ARM64 support when building with MSVC on Win11 [1] I tried out this patch. The reply on that thread had an issue with _mm_pause() in spin_delay(), it turns out we need to use __yield() [2]. I went ahead and fixed that, so ignore that patch on the other thread [1]. The new patch attached that layers on top of your work and supports that platform, there was one minor change that was required:
#ifdef _MSC_VER
/*
* If using Visual C++ on Win64, inline assembly is unavailable. Use a
* _mm_pause intrinsic instead of rep nop. For ARM64, use the __yield()
* intrinsic which emits the YIELD instruction as a hint to the processor.
*/
#if defined(_M_ARM64)
__yield();
#elif defined(_WIN64)
_mm_pause();
#else
/* See comment for gcc code. Same code, MASM syntax */
__asm rep nop;
#endif
#endif /* _MSC_VER */
Visual Studio 2026 (Community)
cl (msvc 19.50.35718 "Microsoft (R) C/C++ Optimizing Compiler Version 19.50.35718 for ARM64")
link 14.50.35718.0
tests are passing, best.
-greg
[1] https://www.postgresql.org/message-id/3c576ad7-d2da-4137-b791-5821da7cc370%40app.fastmail.com
[2] https://learn.microsoft.com/en-us/cpp/intrinsics/arm64-intrinsics?view=msvc-180
Attachments:
[application/octet-stream] v20251123-0001-WIP-ARM64-MSVC-stdatomic.patch (4.4K, 2-v20251123-0001-WIP-ARM64-MSVC-stdatomic.patch)
download | inline diff:
From 295161e09c41658841a902c57f99da54395b20dd Mon Sep 17 00:00:00 2001
From: Greg Burd <[email protected]>
Date: Sun, 23 Nov 2025 07:58:47 -0500
Subject: [PATCH v20251123] WIP ARM64/MSVC stdatomic
---
doc/src/sgml/installation.sgml | 2 +-
meson.build | 15 ++++++++++++++-
src/include/port/spin_delay.h | 7 +++++--
src/port/pg_crc32c_armv8.c | 2 ++
src/tools/msvc_gendef.pl | 8 ++++----
5 files changed, 26 insertions(+), 8 deletions(-)
diff --git a/doc/src/sgml/installation.sgml b/doc/src/sgml/installation.sgml
index fe8d73e1f8c..3f8d512a906 100644
--- a/doc/src/sgml/installation.sgml
+++ b/doc/src/sgml/installation.sgml
@@ -3967,7 +3967,7 @@ configure ... LDFLAGS="-R /usr/sfw/lib:/opt/sfw/lib:/usr/local/lib"
<sect3 id="install-windows-full-64-bit">
<title>Special Considerations for 64-Bit Windows</title>
<para>
- PostgreSQL will only build for the x64 architecture on 64-bit Windows.
+ PostgreSQL will only build for the x64 and ARM64 architectures on 64-bit Windows.
</para>
<para>
Mixing 32- and 64-bit versions in the same build tree is not supported.
diff --git a/meson.build b/meson.build
index 1a2005e75c4..18637180ab1 100644
--- a/meson.build
+++ b/meson.build
@@ -2158,6 +2158,11 @@ endforeach
if cc.get_id() == 'msvc'
+ # Add ARM64 architecture flag for Windows 11 ARM64 for correct intrensics
+ if host_machine.system() == 'windows' and host_machine.cpu_family() == 'aarch64'
+ add_project_arguments('/arch:armv9.4', language: ['c', 'cpp'])
+ endif
+
cflags_warn += [
# Warnings to disable:
# from /W1:
@@ -2367,6 +2372,11 @@ if host_cpu == 'x86' or host_cpu == 'x86_64'
else
prog = '''
+#ifdef _MSC_VER
+#include <intrin.h>
+#else
+#include <arm_acle.h>
+#endif
#include <nmmintrin.h>
unsigned int crc;
@@ -2450,7 +2460,10 @@ int main(void)
}
'''
- if cc.links(prog, name: '__crc32cb, __crc32ch, __crc32cw, and __crc32cd without -march=armv8-a+crc',
+ if cc.get_id() == 'msvc'
+ cdata.set('USE_ARMV8_CRC32C', 1)
+ have_optimized_crc = true
+ elif cc.links(prog, name: '__crc32cb, __crc32ch, __crc32cw, and __crc32cd without -march=armv8-a+crc',
args: test_c_args)
# Use ARM CRC Extension unconditionally
cdata.set('USE_ARMV8_CRC32C', 1)
diff --git a/src/include/port/spin_delay.h b/src/include/port/spin_delay.h
index c583698af8e..f944c8362da 100644
--- a/src/include/port/spin_delay.h
+++ b/src/include/port/spin_delay.h
@@ -69,9 +69,12 @@ pg_spin_delay(void)
/*
* If using Visual C++ on Win64, inline assembly is unavailable. Use a
- * _mm_pause intrinsic instead of rep nop.
+ * _mm_pause intrinsic instead of rep nop. For ARM64, use the __yield()
+ * intrinsic which emits the YIELD instruction as a hint to the processor.
*/
-#if defined(_WIN64)
+#if defined(_M_ARM64)
+ __yield();
+#elif defined(_WIN64)
_mm_pause();
#else
/* See comment for gcc code. Same code, MASM syntax */
diff --git a/src/port/pg_crc32c_armv8.c b/src/port/pg_crc32c_armv8.c
index 5ba070bb99d..6a155ddde1e 100644
--- a/src/port/pg_crc32c_armv8.c
+++ b/src/port/pg_crc32c_armv8.c
@@ -14,7 +14,9 @@
*/
#include "c.h"
+#ifndef _MSC_VER
#include <arm_acle.h>
+#endif
#include "port/pg_crc32c.h"
diff --git a/src/tools/msvc_gendef.pl b/src/tools/msvc_gendef.pl
index 868aad51b09..c92c94c4775 100644
--- a/src/tools/msvc_gendef.pl
+++ b/src/tools/msvc_gendef.pl
@@ -118,9 +118,9 @@ sub writedef
{
my $isdata = $def->{$f} eq 'data';
- # Strip the leading underscore for win32, but not x64
+ # Strip the leading underscore for win32, but not x64 and aarch64
$f =~ s/^_//
- unless ($arch eq "x86_64");
+ unless ($arch eq "x86_64" || $arch eq "aarch64");
# Emit just the name if it's a function symbol, or emit the name
# decorated with the DATA option for variables.
@@ -141,7 +141,7 @@ sub writedef
sub usage
{
die("Usage: msvc_gendef.pl --arch <arch> --deffile <deffile> --tempdir <tempdir> files-or-directories\n"
- . " arch: x86 | x86_64\n"
+ . " arch: x86 | x86_64 | aarch64\n"
. " deffile: path of the generated file\n"
. " tempdir: directory for temporary files\n"
. " files or directories: object files or directory containing object files\n"
@@ -158,7 +158,7 @@ GetOptions(
'tempdir:s' => \$tempdir,) or usage();
usage("arch: $arch")
- unless ($arch eq 'x86' || $arch eq 'x86_64');
+ unless ($arch eq 'x86' || $arch eq 'x86_64' || $arch eq 'aarch64');
my @files;
--
2.52.0.windows.1
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