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Commitaac831c

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Use auxv to check for CRC32 instructions on ARM.
Previously we probed for CRC32 instructions by testing if they causedSIGILL. Some have expressed doubts about that technique, the Linuxdocumentation advises not to use it, and it's not exactly beautiful.Now that more operating systems expose CPU features to userspace via theELF loader in approximately the same way, let's use that instead.This is expected to work on Linux, FreeBSD and recent OpenBSD.OpenBSD/ARM has not been tested and is not present in our build farm,but the API matches FreeBSD.On macOS, compilers use a more recent baseline ISA so the runtime testmechanism isn't reached. (A similar situation is expected forWindows/ARM when that port lands.)On NetBSD, runtime feature probing is lost for armv8-a builds. It lookspotentially doable with sysctl following the example of the cpuctlprogram; patches are welcome.No back-patch for now, since we don't have any evidence of actualbreakage from the previous technique.Suggested-by: Bastien Roucariès <rouca@debian.org>Discussion:https://postgr.es/m/4496616.iHFcN1HehY%40portable-bastien
1 parentea15816 commitaac831c

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5 files changed

+34
-44
lines changed

5 files changed

+34
-44
lines changed

‎configure

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -15144,7 +15144,7 @@ fi
1514415144
LIBS_including_readline="$LIBS"
1514515145
LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
1514615146

15147-
for ac_func in backtrace_symbols copyfile copy_file_range getifaddrs getpeerucred inet_pton kqueue mbstowcs_l memset_s posix_fallocate ppoll pthread_is_threaded_np setproctitle setproctitle_fast strchrnul strsignal syncfs sync_file_range uselocale wcstombs_l
15147+
for ac_func in backtrace_symbols copyfile copy_file_rangeelf_aux_info getauxvalgetifaddrs getpeerucred inet_pton kqueue mbstowcs_l memset_s posix_fallocate ppoll pthread_is_threaded_np setproctitle setproctitle_fast strchrnul strsignal syncfs sync_file_range uselocale wcstombs_l
1514815148
do :
1514915149
as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
1515015150
ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"

‎configure.ac

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1723,6 +1723,8 @@ AC_CHECK_FUNCS(m4_normalize([
17231723
backtrace_symbols
17241724
copyfile
17251725
copy_file_range
1726+
elf_aux_info
1727+
getauxval
17261728
getifaddrs
17271729
getpeerucred
17281730
inet_pton

‎meson.build

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2623,7 +2623,9 @@ func_checks = [
26232623
# when enabling asan the dlopen check doesn't notice that -ldl is actually
26242624
# required. Just checking for dlsym() ought to suffice.
26252625
['dlsym', {'dependencies': [dl_dep],'define':false}],
2626+
['elf_aux_info'],
26262627
['explicit_bzero'],
2628+
['getauxval'],
26272629
['getifaddrs'],
26282630
['getopt', {'dependencies': [getopt_dep, gnugetopt_dep],'skip': always_replace_getopt}],
26292631
['getopt_long', {'dependencies': [getopt_dep, gnugetopt_dep],'skip': always_replace_getopt_long}],

‎src/include/pg_config.h.in

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -125,6 +125,9 @@
125125
/* Define to 1 if you have the <editline/readline.h> header file. */
126126
#undef HAVE_EDITLINE_READLINE_H
127127

128+
/* Define to 1 if you have the `elf_aux_info' function. */
129+
#undef HAVE_ELF_AUX_INFO
130+
128131
/* Define to 1 if you have the <execinfo.h> header file. */
129132
#undef HAVE_EXECINFO_H
130133

@@ -154,6 +157,9 @@
154157
*/
155158
#undef HAVE_GCC__SYNC_INT64_CAS
156159

160+
/* Define to 1 if you have the `getauxval' function. */
161+
#undef HAVE_GETAUXVAL
162+
157163
/* Define to 1 if you have the `getifaddrs' function. */
158164
#undef HAVE_GETIFADDRS
159165

‎src/port/pg_crc32c_armv8_choose.c

Lines changed: 23 additions & 43 deletions
Original file line numberDiff line numberDiff line change
@@ -24,57 +24,37 @@
2424
#include"postgres_fe.h"
2525
#endif
2626

27-
#include<setjmp.h>
28-
#include<signal.h>
27+
#if defined(HAVE_ELF_AUX_INFO)|| defined(HAVE_GETAUXVAL)
28+
#include<sys/auxv.h>
29+
#if defined(__linux__)&& !defined(__aarch64__)&& !defined(HWCAP2_CRC32)
30+
#include<asm/hwcap.h>
31+
#endif
32+
#endif
2933

3034
#include"port/pg_crc32c.h"
3135

32-
33-
staticsigjmp_bufillegal_instruction_jump;
34-
35-
/*
36-
* Probe by trying to execute pg_comp_crc32c_armv8(). If the instruction
37-
* isn't available, we expect to get SIGILL, which we can trap.
38-
*/
39-
staticvoid
40-
illegal_instruction_handler(SIGNAL_ARGS)
41-
{
42-
siglongjmp(illegal_instruction_jump,1);
43-
}
44-
4536
staticbool
4637
pg_crc32c_armv8_available(void)
4738
{
48-
uint64data=42;
49-
intresult;
39+
#if defined(HAVE_ELF_AUX_INFO)
40+
unsigned longvalue;
5041

51-
/*
52-
* Be careful not to do anything that might throw an error while we have
53-
* the SIGILL handler set to a nonstandard value.
54-
*/
55-
pqsignal(SIGILL,illegal_instruction_handler);
56-
if (sigsetjmp(illegal_instruction_jump,1)==0)
57-
{
58-
/* Rather than hard-wiring an expected result, compare to SB8 code */
59-
result= (pg_comp_crc32c_armv8(0,&data,sizeof(data))==
60-
pg_comp_crc32c_sb8(0,&data,sizeof(data)));
61-
}
62-
else
63-
{
64-
/* We got the SIGILL trap */
65-
result=-1;
66-
}
67-
pqsignal(SIGILL,SIG_DFL);
68-
69-
#ifndefFRONTEND
70-
/* We don't expect this case, so complain loudly */
71-
if (result==0)
72-
elog(ERROR,"crc32 hardware and software results disagree");
73-
74-
elog(DEBUG1,"using armv8 crc32 hardware = %d", (result>0));
42+
#ifdef__aarch64__
43+
returnelf_aux_info(AT_HWCAP,&value,sizeof(value))==0&&
44+
(value&HWCAP_CRC32)!=0;
45+
#else
46+
returnelf_aux_info(AT_HWCAP2,&value,sizeof(value))==0&&
47+
(value&HWCAP2_CRC32)!=0;
48+
#endif
49+
#elif defined(HAVE_GETAUXVAL)
50+
#ifdef__aarch64__
51+
return (getauxval(AT_HWCAP)&HWCAP_CRC32)!=0;
52+
#else
53+
return (getauxval(AT_HWCAP2)&HWCAP2_CRC32)!=0;
54+
#endif
55+
#else
56+
return false;
7557
#endif
76-
77-
return (result>0);
7858
}
7959

8060
/*

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