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Improve our method for probing the availability of ARM CRC instructions.

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Instead of depending on glibc's getauxval() function, just try to execute
the CRC code, and trap SIGILL if that happens.

Thomas Munro

Discussion: https://postgr.es/m/HE1PR0801MB1323D171938EABC04FFE7FA9E3110@HE1PR0801MB1323.eurprd08.prod.outlook.com
This commit is contained in:
Tom Lane
2018-05-02 18:06:43 -04:00
parent 40f52b16dd
commit 1c72ec6f49
4 changed files with 29 additions and 73 deletions
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3
src/include/pg_config.h.in
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@ -239,9 +239,6 @@
/* Define to 1 if you have the `getaddrinfo' function. */
#undef HAVE_GETADDRINFO
/* Define to 1 if you have the `getauxval' function. */
#undef HAVE_GETAUXVAL
/* Define to 1 if you have the `gethostbyname_r' function. */
#undef HAVE_GETHOSTBYNAME_R

33
src/port/pg_crc32c_armv8_choose.c
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@ -8,10 +8,6 @@
* computation. Otherwise, fall back to the pure software implementation
* (slicing-by-8).
*
* XXX: The glibc-specific getauxval() function, with the HWCAP_CRC32
* flag, is used to determine if the CRC Extension is available on the
* current platform. Is there a more portable way to determine that?
*
* Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
@ -24,17 +20,38 @@
#include "c.h"
#include <sys/auxv.h>
#include <asm/hwcap.h>
#include <setjmp.h>
#include "libpq/pqsignal.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(int signo)
{
siglongjmp(illegal_instruction_jump, 1);
}
static bool
pg_crc32c_armv8_available(void)
{
unsigned long auxv = getauxval(AT_HWCAP);
uint64 data = 42;
bool result;
return (auxv & HWCAP_CRC32) != 0;
pqsignal(SIGILL, illegal_instruction_handler);
if (sigsetjmp(illegal_instruction_jump, 1) == 0)
result = (pg_comp_crc32c_armv8(0, &data, sizeof(data)) == 0xdd439b0d);
else
result = false;
pqsignal(SIGILL, SIG_DFL);
return result;
}
/*