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/*-------------------------------------------------------------------------
*
* pg_crc32c_armv8_choose.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).
*
* Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/port/pg_crc32c_armv8_choose.c
*
*-------------------------------------------------------------------------
*/
#ifndef FRONTEND
#include "postgres.h"
#else
#include "postgres_fe.h"
#endif
#include <setjmp.h>
#include <signal.h>
#include "port/pg_crc32c.h"
static sigjmp_buf illegal_instruction_jump;
/*
* Probe by trying to execute pg_comp_crc32c_armv8(). If the instruction
* isn't available, we expect to get SIGILL, which we can trap.
*/
static void
illegal_instruction_handler(SIGNAL_ARGS)
{
siglongjmp(illegal_instruction_jump, 1);
}
static bool
pg_crc32c_armv8_available(void)
{
uint64 data = 42;
int result;
/*
* Be careful not to do anything that might throw an error while we have
* the SIGILL handler set to a nonstandard value.
*/
pqsignal(SIGILL, illegal_instruction_handler);
if (sigsetjmp(illegal_instruction_jump, 1) == 0)
{
/* Rather than hard-wiring an expected result, compare to SB8 code */
result = (pg_comp_crc32c_armv8(0, &data, sizeof(data)) ==
pg_comp_crc32c_sb8(0, &data, sizeof(data)));
}
else
{
/* We got the SIGILL trap */
result = -1;
}
pqsignal(SIGILL, SIG_DFL);
#ifndef FRONTEND
/* We don't expect this case, so complain loudly */
if (result == 0)
elog(ERROR, "crc32 hardware and software results disagree");
elog(DEBUG1, "using armv8 crc32 hardware = %d", (result > 0));
#endif
return (result > 0);
}
/*
* 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);
}
pg_crc32c (*pg_comp_crc32c) (pg_crc32c crc, const void *data, size_t len) = pg_comp_crc32c_choose;
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