[PATCH v2] libstdc++: Add support for POWER9 DARN instruction to std::random_device
Jonathan Wakely
jwakely@redhat.com
Wed Nov 3 15:02:38 GMT 2021
On Wed, 3 Nov 2021 at 15:01, Jonathan Wakely wrote:
> Any feedback from POWER maintainers about this? I'd like to push it soon
> if there's nothing wrong with it.
>
With the updated patch attached again this time ...
> On Wed, 20 Oct 2021 at 14:00, Jonathan Wakely via Libstdc++ <
> libstdc++@gcc.gnu.org> wrote:
>
>> On 20/10/21 10:12 +0100, Jonathan Wakely wrote:
>> >On 19/10/21 17:47 +0100, Jonathan Wakely wrote:
>> >>The ISA-3.0 instruction set includes DARN ("deliver a random number")
>> >>which can be used similar to the existing support for RDRAND and RDSEED.
>> >>
>> >>libstdc++-v3/ChangeLog:
>> >>
>> >> * src/c++11/random.cc (USE_DARN): Define.
>> >> (__ppc_darn): New function to use POWER9 DARN instruction.
>> >> (Which): Add 'darn' enumerator.
>> >> (which_source): Check for __ppc_darn.
>> >> (random_device::_M_init): Support "darn" and "hw" tokens.
>> >> (random_device::_M_getentropy): Add darn to switch.
>> >> * testsuite/26_numerics/random/random_device/cons/token.cc:
>> >> Check "darn" token.
>> >> * testsuite/26_numerics/random/random_device/entropy.cc:
>> >> Likewise.
>> >>
>> >>Tested powerpc64le-linux (power8 and power9) and x86_64-linux.
>> >>
>> >>The new "darn" (power-specific) and "hw" (x86 and power)
>> >>strings should be documented, but I'll do that if this gets committed.
>> >>
>> >>Most of this patch is just "more of the same", similar to the existing
>> >>code for RDRAND and RDSEED on x86, but the parts of the patch I'd like
>> >>more eyes on are:
>> >>
>> >>
>> >>+#elif defined __powerpc__ && defined __BUILTIN_CPU_SUPPORTS__
>> >>+# define USE_DARN 1
>> >>#endif
>> >
>> >This means DARN can only be used when __builtin_cpu_supports is
>> >available, which means glibc 2.23 ... is that acceptable? It means
>> >RHEL 7 wouldn't be able to use DARN, but RHEL 8 would.
>> >
>> >There certainly are POWER9 machines running RHEL 7 and similar
>> >vintages (the GCC compile farm has one) so if there's another way to
>> >check for ISA 3.0 then I could use that.
>> >
>> >If __POWER9_VECTOR__ is defined when building libstdc++, presumably
>> >that means the whole library can only be run on POWER9 hardware. So
>> >would that mean we don't need to check __builtin_cpu_supports("darn")
>> >when __POWER9_VECTOR__ is defined? Or is it possible to build with
>> >-mcpu=power8 -mpower9-vector and run it on h/w without the DARN
>> >instruction?
>> >
>> >Also, I forgot to add a configure check that the assembler supports
>> >darn, which is another prerequisite for using it here.
>> >
>> >>@@ -135,6 +137,15 @@ namespace std _GLIBCXX_VISIBILITY(default)
>> >>#endif
>> >>#endif
>> >>
>> >>+#ifdef USE_DARN
>> >>+ unsigned int
>> >>+ __attribute__((target("power9")))
>> >
>> >Oops, that should be "cpu=power9".
>> >
>> >With that change it works on a POWER9 machine (9009-42A) with glibc
>> >2.34 and binutils 2.35.
>> >
>>
>> Here's the updated patch with a configure check for assembler support,
>> and the target attribute fixed.
>>
>> This still requires Glibc 2.23 for __builtin_cpu_supports, which I'm
>> assuming is acceptable.
>>
>>
>>
-------------- next part --------------
commit a6f925407dd05c593b230da1627435adc53584f8
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Wed Oct 20 09:25:24 2021
libstdc++: Add support for POWER9 DARN instruction to std::random_device
The ISA-3.0 instruction set includes DARN ("deliver a random number")
which can be used similar to the existing support for RDRAND and RDSEED.
libstdc++-v3/ChangeLog:
* acinclude.m4 (GLIBCXX_CHECK_PPC_DARN): Check assembler.
* config.h.in: Regenerate.
* configure: Regenerate.
* configure.ac: Use GLIBCXX_CHECK_PPC_DARN.
* src/c++11/random.cc [_GLIBCXX_PPC_DARN] (USE_DARN): Define.
(__ppc_darn): New function to use POWER9 DARN instruction.
(Which): Add 'darn' enumerator.
(which_source): Check for __ppc_darn.
(random_device::_M_init): Support "darn" and "hw" tokens.
(random_device::_M_getentropy): Add darn to switch.
* testsuite/26_numerics/random/random_device/cons/token.cc:
Check "darn" token.
* testsuite/26_numerics/random/random_device/entropy.cc:
Likewise.
diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
index 90ecc4a87a2..9ff9ceb20ac 100644
--- a/libstdc++-v3/acinclude.m4
+++ b/libstdc++-v3/acinclude.m4
@@ -4100,6 +4100,27 @@ AC_DEFUN([GLIBCXX_CHECK_X86_RDSEED], [
AC_MSG_RESULT($ac_cv_x86_rdseed)
])
+dnl
+dnl Check whether darn is supported in the assembler.
+AC_DEFUN([GLIBCXX_CHECK_PPC_DARN], [
+ AC_MSG_CHECKING([for darn support in assembler])
+ AC_CACHE_VAL(ac_cv_ppc_darn, [
+ ac_cv_ppc_darn=no
+ case "$target" in
+ powerpc*-*-*)
+ AC_TRY_COMPILE(, [
+ signed int x;
+ __asm__ __volatile__ (".machine power9; darn %0,0;": "=r" (x));
+ ], [ac_cv_ppc_darn=yes], [ac_cv_ppc_darn=no])
+ esac
+ ])
+ if test $ac_cv_ppc_darn = yes; then
+ AC_DEFINE(_GLIBCXX_PPC_DARN, 1,
+ [ Defined if as can handle darn. ])
+ fi
+ AC_MSG_RESULT($ac_cv_ppc_darn)
+])
+
dnl
dnl Check whether get_nprocs is available in <sys/sysinfo.h>, and define _GLIBCXX_USE_GET_NPROCS.
dnl
diff --git a/libstdc++-v3/configure.ac b/libstdc++-v3/configure.ac
index 2d68b3672b9..1189c68c380 100644
--- a/libstdc++-v3/configure.ac
+++ b/libstdc++-v3/configure.ac
@@ -467,6 +467,8 @@ GCC_CHECK_ASSEMBLER_HWCAP
GLIBCXX_CHECK_X86_RDRAND
# Check if assembler supports rdseed opcode.
GLIBCXX_CHECK_X86_RDSEED
+# Check if assembler supports darn opcode.
+GLIBCXX_CHECK_PPC_DARN
# This depends on GLIBCXX_ENABLE_SYMVERS and GLIBCXX_IS_NATIVE.
GLIBCXX_CONFIGURE_TESTSUITE
diff --git a/libstdc++-v3/src/c++11/random.cc b/libstdc++-v3/src/c++11/random.cc
index 4b64bde00ea..213ad691837 100644
--- a/libstdc++-v3/src/c++11/random.cc
+++ b/libstdc++-v3/src/c++11/random.cc
@@ -37,6 +37,9 @@
# ifdef _GLIBCXX_X86_RDSEED
# define USE_RDSEED 1
# endif
+#elif defined __powerpc__ && defined __BUILTIN_CPU_SUPPORTS__ \
+ && defined _GLIBCXX_PPC_DARN
+# define USE_DARN 1
#endif
#include <cerrno>
@@ -69,7 +72,7 @@
#if defined _GLIBCXX_USE_CRT_RAND_S || defined _GLIBCXX_USE_DEV_RANDOM
// The OS provides a source of randomness we can use.
# pragma GCC poison _M_mt
-#elif defined USE_RDRAND || defined USE_RDSEED
+#elif defined USE_RDRAND || defined USE_RDSEED || defined USE_DARN
// Hardware instructions might be available, but use cpuid checks at runtime.
# pragma GCC poison _M_mt
// If the runtime cpuid checks fail we'll use a linear congruential engine.
@@ -135,6 +138,15 @@ namespace std _GLIBCXX_VISIBILITY(default)
#endif
#endif
+#ifdef USE_DARN
+ unsigned int
+ __attribute__((target("cpu=power9")))
+ __ppc_darn(void*)
+ {
+ return __builtin_darn_32();
+ }
+#endif
+
#ifdef _GLIBCXX_USE_CRT_RAND_S
unsigned int
__winxp_rand_s(void*)
@@ -193,11 +205,16 @@ namespace std _GLIBCXX_VISIBILITY(default)
}
#endif
- enum Which {
- rand_s = 1, rdseed = 2, rdrand = 4, device_file = 8, prng = 16,
+ enum Which : unsigned {
+ device_file = 1, prng = 2, rand_s = 4,
+ rdseed = 64, rdrand = 128, darn = 256,
any = 0xffff
};
+ constexpr Which
+ operator|(Which l, Which r) noexcept
+ { return Which(unsigned(l) | unsigned(r)); }
+
inline Which
which_source(random_device::result_type (*func [[maybe_unused]])(void*),
void* file [[maybe_unused]])
@@ -221,6 +238,11 @@ namespace std _GLIBCXX_VISIBILITY(default)
return rdrand;
#endif
+#ifdef USE_DARN
+ if (func == &__ppc_darn)
+ return darn;
+#endif
+
#ifdef _GLIBCXX_USE_DEV_RANDOM
if (file != nullptr)
return device_file;
@@ -269,6 +291,14 @@ namespace std _GLIBCXX_VISIBILITY(default)
else if (token == "rdrand" || token == "rdrnd")
which = rdrand;
#endif // USE_RDRAND
+#ifdef USE_DARN
+ else if (token == "darn")
+ which = darn;
+#endif
+#if defined USE_RDRAND || defined USE_RDSEED || defined USE_DARN
+ else if (token == "hw" || token == "hardware")
+ which = rdrand | rdseed | darn;
+#endif
#ifdef _GLIBCXX_USE_CRT_RAND_S
else if (token == "rand_s")
which = rand_s;
@@ -346,6 +376,17 @@ namespace std _GLIBCXX_VISIBILITY(default)
}
#endif // USE_RDRAND
+#ifdef USE_DARN
+ if (which & darn)
+ {
+ if (__builtin_cpu_supports("darn"))
+ {
+ _M_func = &__ppc_darn;
+ return;
+ }
+ }
+#endif // USE_DARN
+
#ifdef _GLIBCXX_USE_DEV_RANDOM
if (which & device_file)
{
@@ -497,6 +538,7 @@ namespace std _GLIBCXX_VISIBILITY(default)
{
case rdrand:
case rdseed:
+ case darn:
return (double) max;
case rand_s:
case prng:
diff --git a/libstdc++-v3/testsuite/26_numerics/random/random_device/cons/token.cc b/libstdc++-v3/testsuite/26_numerics/random/random_device/cons/token.cc
index aeb7403e830..d6ac3a37c64 100644
--- a/libstdc++-v3/testsuite/26_numerics/random/random_device/cons/token.cc
+++ b/libstdc++-v3/testsuite/26_numerics/random/random_device/cons/token.cc
@@ -51,8 +51,9 @@ test03()
{
// At least one of these tokens should be valid.
const std::string tokens[] = {
- "rdseed", "rdrand", "rand_s", "/dev/urandom", "/dev/random", "mt19937",
- "prng"
+ "rdseed", "rdrand", "darn",
+ "rand_s", "/dev/urandom", "/dev/random",
+ "mt19937", "prng"
};
int count = 0;
for (const std::string& token : tokens)
diff --git a/libstdc++-v3/testsuite/26_numerics/random/random_device/entropy.cc b/libstdc++-v3/testsuite/26_numerics/random/random_device/entropy.cc
index 9ef1538d2bb..6f3ebb1b38e 100644
--- a/libstdc++-v3/testsuite/26_numerics/random/random_device/entropy.cc
+++ b/libstdc++-v3/testsuite/26_numerics/random/random_device/entropy.cc
@@ -22,7 +22,7 @@ test01()
VERIFY( entropy <= max );
}
- for (auto token : { "rdrand", "rdseed" })
+ for (auto token : { "rdrand", "rdseed", "darn", "hw" })
if (__gnu_test::random_device_available(token))
{
const double entropy = std::random_device(token).entropy();
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