v4-0006-Centralize-detection-of-CPU-features-Arm-take-1.patch

From a3e9a1302d710f9fa6c48594144a82fe0c3988d6 Mon Sep 17 00:00:00 2001
From: John Naylor <john.naylor@postgresql.org>
Date: Thu, 19 Feb 2026 18:27:02 +0700
Subject: [PATCH v4 6/6] Centralize detection of CPU features Arm, take 1

---
 src/include/port/pg_cpu.h      | 25 ++++++++++++
 src/port/pg_cpu_armv8.c        | 74 +++++++++++++++-------------------
 src/port/pg_crc32c_armv8.c     | 20 +++++++++
 src/port/pg_popcount_aarch64.c | 26 +-----------
 4 files changed, 80 insertions(+), 65 deletions(-)

diff --git a/src/include/port/pg_cpu.h b/src/include/port/pg_cpu.h
index 3c70fd43a23..3687e025083 100644
--- a/src/include/port/pg_cpu.h
+++ b/src/include/port/pg_cpu.h
@@ -48,6 +48,31 @@ x86_feature_available(X86FeatureId feature)
 	return X86Features[feature];
 }
 
+#elif defined(__arm__) || defined(__arm) || defined(__aarch64__)
+
+typedef enum ArmFeatureId
+{
+	/* Have we run feature detection? */
+	INIT_PG_ARM,
+
+	PG_ARM_CRC32,
+	PG_ARM_SVE,
+}			ArmFeatureId;
+#define ArmFeaturesSize (PG_ARM_SVE + 1)
+
+extern PGDLLIMPORT bool ArmFeatures[];
+
+extern void set_arm_features(void);
+
+static inline bool
+arm_feature_available(ArmFeatureId feature)
+{
+	if (ArmFeatures[INIT_PG_ARM] == false)
+		set_arm_features();
+
+	return ArmFeatures[feature];
+}
+
 #endif							/* defined(USE_SSE2) || defined(__i386__) */
 
 #endif							/* PG_CPU_H */
diff --git a/src/port/pg_cpu_armv8.c b/src/port/pg_cpu_armv8.c
index 6c22704b5fa..59a9229b71d 100644
--- a/src/port/pg_cpu_armv8.c
+++ b/src/port/pg_cpu_armv8.c
@@ -1,12 +1,7 @@
 /*-------------------------------------------------------------------------
  *
  * pg_cpu_armv8.c
- *	  Choose between ARMv8 and software CRC-32C implementation.
- *
- * On first call, checks if the CPU we're running on supports the ARMv8
- * CRC Extension. If it does, use the special instructions for CRC-32C
- * computation. Otherwise, fall back to the pure software implementation
- * (slicing-by-8).
+ *	  Runtime CPU feature detection for Arm-v8
  *
  * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
@@ -41,27 +36,41 @@
 #endif
 #endif
 
-#include "port/pg_crc32c.h"
+#include "port/pg_cpu.h"
+
+
+bool		ArmFeatures[ArmFeaturesSize] = {0};
 
-static bool
-pg_crc32c_armv8_available(void)
+static inline unsigned long
+pg_getauxval(unsigned long at_hwcap)
 {
 #if defined(HAVE_ELF_AUX_INFO)
 	unsigned long value;
 
-#ifdef __aarch64__
-	return elf_aux_info(AT_HWCAP, &value, sizeof(value)) == 0 &&
-		(value & HWCAP_CRC32) != 0;
-#else
-	return elf_aux_info(AT_HWCAP2, &value, sizeof(value)) == 0 &&
-		(value & HWCAP2_CRC32) != 0;
-#endif
+	if (elf_aux_info(at_hwcap, &value, sizeof(value)) == 0)
+		return value;
+	else
+		return 0;
 #elif defined(HAVE_GETAUXVAL)
+	return getauxval(at_hwcap);
+#endif
+}
+
+void
+set_arm_features(void)
+{
+#if HAVE_GETAUXVAL || HAVE_ELF_AUX_INFO
 #ifdef __aarch64__
-	return (getauxval(AT_HWCAP) & HWCAP_CRC32) != 0;
+	unsigned long hwcap = pg_getauxval(AT_HWCAP);
+
+	ArmFeatures[PG_ARM_CRC32] = (hwcap & HWCAP_CRC32) != 0;
+	ArmFeatures[PG_ARM_SVE] = (hwcap & HWCAP_SVE) != 0;
 #else
-	return (getauxval(AT_HWCAP2) & HWCAP2_CRC32) != 0;
+	unsigned long hwcap2 = pg_getauxval(AT_HWCAP2);
+
+	ArmFeatures[PG_ARM_CRC32] = (hwcap2 & HWCAP2_CRC32) != 0;
 #endif
+
 #elif defined(__NetBSD__)
 	/*
 	 * On NetBSD we can read the Instruction Set Attribute Registers via
@@ -92,9 +101,9 @@ pg_crc32c_armv8_available(void)
 	len = sizeof(sysctlbuf);
 	memset(sysctlbuf, 0, len);
 	if (sysctlbyname(path, sysctlbuf, &len, NULL, 0) != 0)
-		return false;			/* perhaps kernel is 64-bit and we aren't? */
+		return;					/* perhaps kernel is 64-bit and we aren't? */
 	if (len != expected_len)
-		return false;			/* kernel API change? */
+		return;					/* kernel API change? */
 
 	/* Fetch the CRC32 field from ISAR0. */
 	fld = (ISAR0 >> ISAR0_CRC32_BITPOS) & WIDTHMASK(ISAR0_CRC32_BITWIDTH);
@@ -104,27 +113,10 @@ pg_crc32c_armv8_available(void)
 	 * (CRC32B/CRC32H/CRC32W/CRC32X/CRC32CB/CRC32CH/CRC32CW/CRC32CX).  Assume
 	 * that any future nonzero value will be a superset of 1.
 	 */
-	return (fld != 0);
-#else
-	return false;
-#endif
-}
+	ArmFeatures[PG_ARM_CRC32] = (fld != 0);
+#endif							/* __NetBSD__ */
 
-/*
- * This gets called on the first call. It replaces the function pointer
- * so that subsequent calls are routed directly to the chosen implementation.
- */
-static pg_crc32c
-pg_comp_crc32c_choose(pg_crc32c crc, const void *data, size_t len)
-{
-	if (pg_crc32c_armv8_available())
-		pg_comp_crc32c = pg_comp_crc32c_armv8;
-	else
-		pg_comp_crc32c = pg_comp_crc32c_sb8;
-
-	return pg_comp_crc32c(crc, data, len);
+	ArmFeatures[INIT_PG_ARM] = true;
 }
 
-pg_crc32c	(*pg_comp_crc32c) (pg_crc32c crc, const void *data, size_t len) = pg_comp_crc32c_choose;
-
-#endif      /* __arm__ || __arm || __aarch64__ */
+#endif							/* __arm__ || __arm || __aarch64__ */
diff --git a/src/port/pg_crc32c_armv8.c b/src/port/pg_crc32c_armv8.c
index 9ca0f728d39..a02264a00dc 100644
--- a/src/port/pg_crc32c_armv8.c
+++ b/src/port/pg_crc32c_armv8.c
@@ -20,8 +20,11 @@
 #include <arm_acle.h>
 #endif
 
+#include "port/pg_cpu.h"
 #include "port/pg_crc32c.h"
 
+static pg_crc32c pg_comp_crc32c_choose(pg_crc32c crc, const void *data, size_t len);
+
 pg_crc32c
 pg_comp_crc32c_armv8(pg_crc32c crc, const void *data, size_t len)
 {
@@ -77,3 +80,20 @@ pg_comp_crc32c_armv8(pg_crc32c crc, const void *data, size_t len)
 
 	return crc;
 }
+
+/*
+ * This gets called on the first call. It replaces the function pointer
+ * so that subsequent calls are routed directly to the chosen implementation.
+ */
+static pg_crc32c
+pg_comp_crc32c_choose(pg_crc32c crc, const void *data, size_t len)
+{
+	if (arm_feature_available(PG_ARM_CRC32))
+		pg_comp_crc32c = pg_comp_crc32c_armv8;
+	else
+		pg_comp_crc32c = pg_comp_crc32c_sb8;
+
+	return pg_comp_crc32c(crc, data, len);
+}
+
+pg_crc32c	(*pg_comp_crc32c) (pg_crc32c crc, const void *data, size_t len) = pg_comp_crc32c_choose;
diff --git a/src/port/pg_popcount_aarch64.c b/src/port/pg_popcount_aarch64.c
index f474ef45510..37adff67ce8 100644
--- a/src/port/pg_popcount_aarch64.c
+++ b/src/port/pg_popcount_aarch64.c
@@ -18,17 +18,10 @@
 
 #ifdef USE_SVE_POPCNT_WITH_RUNTIME_CHECK
 #include <arm_sve.h>
-
-#if defined(HAVE_ELF_AUX_INFO) || defined(HAVE_GETAUXVAL)
-#include <sys/auxv.h>
-/* Ancient glibc releases don't include the HWCAPxxx macros in sys/auxv.h */
-#if defined(__linux__) && !defined(HWCAP_SVE)
-#include <asm/hwcap.h>
-#endif
-#endif
 #endif
 
 #include "port/pg_bitutils.h"
+#include "port/pg_cpu.h"
 
 /*
  * The Neon versions are built regardless of whether we are building the SVE
@@ -56,25 +49,10 @@ static uint64 pg_popcount_masked_choose(const char *buf, int bytes, bits8 mask);
 uint64		(*pg_popcount_optimized) (const char *buf, int bytes) = pg_popcount_choose;
 uint64		(*pg_popcount_masked_optimized) (const char *buf, int bytes, bits8 mask) = pg_popcount_masked_choose;
 
-static inline bool
-pg_popcount_sve_available(void)
-{
-#ifdef HAVE_ELF_AUX_INFO
-	unsigned long value;
-
-	return elf_aux_info(AT_HWCAP, &value, sizeof(value)) == 0 &&
-		(value & HWCAP_SVE) != 0;
-#elif defined(HAVE_GETAUXVAL)
-	return (getauxval(AT_HWCAP) & HWCAP_SVE) != 0;
-#else
-	return false;
-#endif
-}
-
 static inline void
 choose_popcount_functions(void)
 {
-	if (pg_popcount_sve_available())
+	if (arm_feature_available(PG_ARM_SVE))
 	{
 		pg_popcount_optimized = pg_popcount_sve;
 		pg_popcount_masked_optimized = pg_popcount_masked_sve;
-- 
2.53.0