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.
commit a6f925407dd05c593b230da1627435adc53584f8
Author: Jonathan Wakely <jwak...@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();
