[dpdk-dev] [PATCH v2 2/2] eal: resolve getentropy at run time for random seed

[Dan Gora]

The getentropy() function was introduced into glibc v2.25 and so is
not available on all supported platforms.  Previously, if DPDK was
compiled (using meson) on a system which has getentropy(), it would
introduce a dependency on glibc v2.25 which would prevent that binary
from running on a system with an older glibc.  Similarly if DPDK was
compiled on a system which did not have getentropy(), getentropy()
could not be used even if the execution system supported it.

Introduce a new static function, __rte_getentropy() which will try to
resolve the getentropy() function dynamically using dlopen()/dlsym(),
returning failure if the getentropy() function cannot be resolved or
if it fails.

This also allows getentropy() to be used as the random seed source
when the traditional Makefile build for DPDK is used.

Signed-off-by: Dan Gora <dg at adax.com>
---
 lib/librte_eal/common/rte_random.c | 35 +++++++++++++++++++++++++-----
 lib/librte_eal/meson.build         |  3 ---
 2 files changed, 29 insertions(+), 9 deletions(-)

diff --git a/lib/librte_eal/common/rte_random.c b/lib/librte_eal/common/rte_random.c
index 2c84c8527..3a05b23db 100644
--- a/lib/librte_eal/common/rte_random.c
+++ b/lib/librte_eal/common/rte_random.c
@@ -7,6 +7,7 @@
 #endif
 #include <stdlib.h>
 #include <unistd.h>
+#include <dlfcn.h>
 
 #include <rte_branch_prediction.h>
 #include <rte_cycles.h>
@@ -176,18 +177,40 @@ rte_rand_max(uint64_t upper_bound)
 	return res;
 }
 
+/* Try to use the getentropy() function from glibc >= 2.25 */
+static int
+__rte_getentropy(uint64_t *ge_seed)
+{
+	void *handle = NULL;
+	void **sym;
+	int (*getentropy_p)(void *__buffer, size_t __length);
+	int gc_rc;
+
+	handle = dlopen("libc.so.6", RTLD_LAZY);
+	if (!handle)
+		return -1;
+
+	sym = dlsym(handle, "getentropy");
+	if (!sym || !*sym) {
+		/* Cannot resolve getentropy */
+		dlclose(handle);
+		return -1;
+	}
+
+	getentropy_p = (int (*)(void *, size_t)) sym;
+	gc_rc = (*getentropy_p)((void *)ge_seed, sizeof(*ge_seed));
+	dlclose(handle);
+	return gc_rc;
+}
+
 static uint64_t
 __rte_random_initial_seed(void)
 {
-#ifdef RTE_LIBEAL_USE_GETENTROPY
-	int ge_rc;
 	uint64_t ge_seed;
 
-	ge_rc = getentropy(&ge_seed, sizeof(ge_seed));
-
-	if (ge_rc == 0)
+	if (__rte_getentropy(&ge_seed) == 0)
 		return ge_seed;
-#endif
+
 #if defined(RTE_ARCH_X86)
 	/* first fallback: rdseed instruction, if available */
 	if (rte_cpu_get_flag_enabled(RTE_CPUFLAG_RDSEED)) {
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
-- 
2.24.1.425.g7034cd094b