On 2020-04-16 01:59, Dan Gora wrote:
> Instead of choosing to use getentropy() or the rdseed instruction for
> the random number generator entropy source using compilation flags,
> determine the best source at run time.
I like this idea.
> This is accomplished by defining a weak symbol for getentropy(),
> checking that the compiler can generate the rdseed instruction even if
> the compilation platform does not natively support it, and checking for
> the availability of the rdseed instruction on the execution platform
> using rte_cpu_get_flag_enabled().
>
> If neither getentropy() or rdseed is available, rte_get_timer_cycles()
> will be continue to be used as the entropy source.
>
> This also allows non-meson builds to use getentropy().
>
> Signed-off-by: Dan Gora <d...@adax.com>
> ---
> v2:
> * Rebase to latest master.
> * Fix spelling of "meson".
>
> config/x86/meson.build | 7 +++++++
> lib/librte_eal/common/rte_random.c | 29 ++++++++++++++++++++++++-----
> lib/librte_eal/meson.build | 3 ---
> mk/rte.cpuflags.mk | 8 ++++++++
> 4 files changed, 39 insertions(+), 8 deletions(-)
>
> diff --git a/config/x86/meson.build b/config/x86/meson.build
> index adc857ba2..214b16f2a 100644
> --- a/config/x86/meson.build
> +++ b/config/x86/meson.build
> @@ -20,6 +20,13 @@ if cc.get_define('__SSE4_2__', args: machine_args) == ''
> machine_args += '-msse4'
> endif
>
> +# set -mrdseed if necessary so _rdseed32_step compiles if the
> +# compilation host does not support the RDSEED instruction.
> +if cc.get_define('__RDSEED__', args: machine_args) == '' and
> cc.has_argument('-mrdseed')
> + machine_args += '-mrdseed'
> + message('RDSEED not enabled by default, explicitly setting -mrdseed')
> +endif
> +
> base_flags = ['SSE', 'SSE2', 'SSE3','SSSE3', 'SSE4_1', 'SSE4_2']
> foreach f:base_flags
> dpdk_conf.set('RTE_MACHINE_CPUFLAG_' + f, 1)
> diff --git a/lib/librte_eal/common/rte_random.c
> b/lib/librte_eal/common/rte_random.c
> index 57ec8fb2b..40f8b5aab 100644
> --- a/lib/librte_eal/common/rte_random.c
> +++ b/lib/librte_eal/common/rte_random.c
> @@ -25,6 +25,8 @@ struct rte_rand_state {
>
> static struct rte_rand_state rand_states[RTE_MAX_LCORE];
>
> +__rte_weak int getentropy(void *__buffer, size_t __length);
> +
> static uint32_t
> __rte_rand_lcg32(uint32_t *seed)
> {
> @@ -176,10 +178,24 @@ rte_rand_max(uint64_t upper_bound)
> return res;
> }
>
> +/* Use rte_get_timer_cycles() if the system does not have
> + * genentropy() or the rdseed instruction.
> + */
> +__rte_weak int
> +getentropy(void *__buffer, size_t __length __rte_unused)
> +{
Just make the weak getentropy() to return -1, always.
> + uint64_t *ge_seed = __buffer;
> +#ifdef RTE_MACHINE_CPUFLAG_RDSEED
> + if (rte_cpu_get_flag_enabled(RTE_CPUFLAG_RDSEED))
> + return -1;
> +#endif
> + *ge_seed = rte_get_timer_cycles();
> + return 0;
> +}
> +
> static uint64_t
> __rte_random_initial_seed(void)
> {
> -#ifdef RTE_LIBEAL_USE_GETENTROPY
> int ge_rc;
> uint64_t ge_seed;
>
> @@ -187,15 +203,18 @@ __rte_random_initial_seed(void)
>
> if (ge_rc == 0)
> return ge_seed;
> -#endif
> +
> #ifdef RTE_MACHINE_CPUFLAG_RDSEED
> unsigned int rdseed_low;
> unsigned int rdseed_high;
>
> /* first fallback: rdseed instruction, if available */
> - if (_rdseed32_step(&rdseed_low) == 1 &&
> - _rdseed32_step(&rdseed_high) == 1)
> - return (uint64_t)rdseed_low | ((uint64_t)rdseed_high << 32);
> + if (rte_cpu_get_flag_enabled(RTE_CPUFLAG_RDSEED)) {
Move the variable declarations into this scope.
> + if (_rdseed32_step(&rdseed_low) == 1 &&
> + _rdseed32_step(&rdseed_high) == 1)
> + return (uint64_t)rdseed_low |
> + ((uint64_t)rdseed_high << 32);
> + }
> #endif
> /* second fallback: seed using rdtsc */
> return rte_get_timer_cycles();
> diff --git a/lib/librte_eal/meson.build b/lib/librte_eal/meson.build
> index 0267c3b9d..748359b8c 100644
> --- a/lib/librte_eal/meson.build
> +++ b/lib/librte_eal/meson.build
> @@ -15,9 +15,6 @@ deps += 'kvargs'
> if dpdk_conf.has('RTE_USE_LIBBSD')
> ext_deps += libbsd
> endif
> -if cc.has_function('getentropy', prefix : '#include <unistd.h>')
> - cflags += '-DRTE_LIBEAL_USE_GETENTROPY'
> -endif
> if cc.has_header('getopt.h')
> cflags += ['-DHAVE_GETOPT_H', '-DHAVE_GETOPT', '-DHAVE_GETOPT_LONG']
> endif
> diff --git a/mk/rte.cpuflags.mk b/mk/rte.cpuflags.mk
> index fa8753531..fb7bf8a53 100644
> --- a/mk/rte.cpuflags.mk
> +++ b/mk/rte.cpuflags.mk
> @@ -53,6 +53,14 @@ endif
>
> ifneq ($(filter $(AUTO_CPUFLAGS),__RDSEED__),)
> CPUFLAGS += RDSEED
> +else
> +# If the native environment doesn't define __RDSEED__, see
> +# if the compiler supports -mrdseed.
For which environments is this true?
> +RDSEED_CPUFLAGS := $(shell $(CC) $(MACHINE_CFLAGS) $(WERROR_FLAGS)
> $(EXTRA_CFLAGS) -mrdseed -dM -E - < /dev/null)
> +ifneq ($(filter $(RDSEED_CPUFLAGS),__RDSEED__),)
There are no better ways to achieve this? It seems like a bit of a hack.
> +CPUFLAGS += RDSEED
> +MACHINE_CFLAGS += -mrdseed
> +endif
> endif
>
> ifneq ($(filter $(AUTO_CPUFLAGS),__FSGSBASE__),)
