96 lines
2.4 KiB
C
96 lines
2.4 KiB
C
/*-------------------------------------------------------------------------
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*
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* pg_crc32c_armv8_choose.c
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* Choose between ARMv8 and software CRC-32C implementation.
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*
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* On first call, checks if the CPU we're running on supports the ARMv8
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* CRC Extension. If it does, use the special instructions for CRC-32C
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* computation. Otherwise, fall back to the pure software implementation
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* (slicing-by-8).
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*
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* Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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*
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* IDENTIFICATION
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* src/port/pg_crc32c_armv8_choose.c
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef FRONTEND
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#include "postgres.h"
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#else
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#include "postgres_fe.h"
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#endif
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#include <setjmp.h>
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#include <signal.h>
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#include "port/pg_crc32c.h"
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static sigjmp_buf illegal_instruction_jump;
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/*
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* Probe by trying to execute pg_comp_crc32c_armv8(). If the instruction
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* isn't available, we expect to get SIGILL, which we can trap.
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*/
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static void
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illegal_instruction_handler(SIGNAL_ARGS)
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{
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siglongjmp(illegal_instruction_jump, 1);
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}
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static bool
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pg_crc32c_armv8_available(void)
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{
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uint64 data = 42;
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int result;
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/*
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* Be careful not to do anything that might throw an error while we have
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* the SIGILL handler set to a nonstandard value.
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*/
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pqsignal(SIGILL, illegal_instruction_handler);
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if (sigsetjmp(illegal_instruction_jump, 1) == 0)
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{
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/* Rather than hard-wiring an expected result, compare to SB8 code */
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result = (pg_comp_crc32c_armv8(0, &data, sizeof(data)) ==
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pg_comp_crc32c_sb8(0, &data, sizeof(data)));
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}
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else
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{
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/* We got the SIGILL trap */
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result = -1;
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}
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pqsignal(SIGILL, SIG_DFL);
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#ifndef FRONTEND
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/* We don't expect this case, so complain loudly */
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if (result == 0)
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elog(ERROR, "crc32 hardware and software results disagree");
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elog(DEBUG1, "using armv8 crc32 hardware = %d", (result > 0));
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#endif
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return (result > 0);
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}
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/*
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* This gets called on the first call. It replaces the function pointer
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* so that subsequent calls are routed directly to the chosen implementation.
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*/
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static pg_crc32c
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pg_comp_crc32c_choose(pg_crc32c crc, const void *data, size_t len)
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{
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if (pg_crc32c_armv8_available())
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pg_comp_crc32c = pg_comp_crc32c_armv8;
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else
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pg_comp_crc32c = pg_comp_crc32c_sb8;
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return pg_comp_crc32c(crc, data, len);
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}
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pg_crc32c (*pg_comp_crc32c) (pg_crc32c crc, const void *data, size_t len) = pg_comp_crc32c_choose;
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