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Support runtime CRC feature probing on NetBSD/ARM using sysctl().

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Commit aac831caf left this as a to-do; here's code to do it.
Like the previous patch, this is HEAD-only for now.

Discussion: https://postgr.es/m/4496616.iHFcN1HehY@portable-bastien
This commit is contained in:
Tom Lane 2024-11-25 11:53:26 -05:00
parent 32a2aa77ef
commit 4570b22666
1 changed files with 50 additions and 0 deletions
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50
src/port/pg_crc32c_armv8_choose.c
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@ -31,6 +31,13 @@
#endif
#endif
#if defined(__NetBSD__)
#include <sys/sysctl.h>
#if defined(__aarch64__)
#include <aarch64/armreg.h>
#endif
#endif
#include "port/pg_crc32c.h"
static bool
@ -52,6 +59,49 @@ pg_crc32c_armv8_available(void)
#else
return (getauxval(AT_HWCAP2) & HWCAP2_CRC32) != 0;
#endif
#elif defined(__NetBSD__)
/*
* On NetBSD we can read the Instruction Set Attribute Registers via
* sysctl. For doubtless-historical reasons the sysctl interface is
* completely different on 64-bit than 32-bit, but the underlying
* registers contain the same fields.
*/
#define ISAR0_CRC32_BITPOS 16
#define ISAR0_CRC32_BITWIDTH 4
#define WIDTHMASK(w) ((1 << (w)) - 1)
#define SYSCTL_CPU_ID_MAXSIZE 64
size_t len;
uint64 sysctlbuf[SYSCTL_CPU_ID_MAXSIZE];
#if defined(__aarch64__)
/* We assume cpu0 is representative of all the machine's CPUs. */
const char *path = "machdep.cpu0.cpu_id";
size_t expected_len = sizeof(struct aarch64_sysctl_cpu_id);
#define ISAR0 ((struct aarch64_sysctl_cpu_id *) sysctlbuf)->ac_aa64isar0
#else
const char *path = "machdep.id_isar";
size_t expected_len = 6 * sizeof(int);
#define ISAR0 ((int *) sysctlbuf)[5]
#endif
uint64 fld;
/* Fetch the appropriate set of register values. */
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? */
if (len != expected_len)
return false; /* kernel API change? */
/* Fetch the CRC32 field from ISAR0. */
fld = (ISAR0 >> ISAR0_CRC32_BITPOS) & WIDTHMASK(ISAR0_CRC32_BITWIDTH);
/*
* Current documentation defines only the field values 0 (No CRC32) and 1
* (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