[dpdk-dev] [PATCH] eal: abstract away the auxiliary vector

[Aaron Conole]

Rather than attempting to load the contents of the auxv directly,
prefer to use an exposed API - and if that doesn't exist then attempt
to load the vector.  This is because on some systems, when a user
is downgraded, the /proc/self/auxv file retains the old ownership
and permissions.  The original method of /proc/self/auxv is retained.

This also removes a potential abort() in the code when compiled with
NDEBUG.  A quick parse of the code shows that many (if not all) of
the CPU flag parsing isn't used internally, so it should be okay.

Signed-off-by: Aaron Conole <aconole at redhat.com>
Signed-off-by: Timothy Redaelli <tredaelli at redhat.com>
---
NOTE: These APIs aren't added to the map because I really want
      them to be internal-only.  No other component really needs
      access to them.  I couldn't find a good common internal
      include file which is why they're in the rte_cpuflags.h -
      but if there's a better one, we can spin another version.

 lib/librte_eal/common/arch/arm/rte_cpuflags.c      | 20 ++----
 lib/librte_eal/common/arch/ppc_64/rte_cpuflags.c   | 15 +----
 lib/librte_eal/common/eal_common_cpuflags.c        | 76 ++++++++++++++++++++++
 .../common/include/generic/rte_cpuflags.h          | 13 ++++
 4 files changed, 95 insertions(+), 29 deletions(-)

diff --git a/lib/librte_eal/common/arch/arm/rte_cpuflags.c b/lib/librte_eal/common/arch/arm/rte_cpuflags.c
index 88f1cbe37..496d8b21a 100644
--- a/lib/librte_eal/common/arch/arm/rte_cpuflags.c
+++ b/lib/librte_eal/common/arch/arm/rte_cpuflags.c
@@ -133,22 +133,10 @@ const struct feature_entry rte_cpu_feature_table[] = {
 static void
 rte_cpu_get_features(hwcap_registers_t out)
 {
-	int auxv_fd;
-	_Elfx_auxv_t auxv;
-
-	auxv_fd = open("/proc/self/auxv", O_RDONLY);
-	assert(auxv_fd != -1);
-	while (read(auxv_fd, &auxv, sizeof(auxv)) == sizeof(auxv)) {
-		if (auxv.a_type == AT_HWCAP) {
-			out[REG_HWCAP] = auxv.a_un.a_val;
-		} else if (auxv.a_type == AT_HWCAP2) {
-			out[REG_HWCAP2] = auxv.a_un.a_val;
-		} else if (auxv.a_type == AT_PLATFORM) {
-			if (!strcmp((const char *)auxv.a_un.a_val, PLATFORM_STR))
-				out[REG_PLATFORM] = 0x0001;
-		}
-	}
-	close(auxv_fd);
+	out[REG_HWCAP] = rte_cpu_getauxval(AT_HWCAP);
+	out[REG_HWCAP2] = rte_cpu_getauxval(AT_HWCAP2);
+	if (!rte_cpu_strcmp_auxval(AT_PLATFORM, PLATFORM_STR))
+		out[REG_PLATFORM] = 0x0001;
 }
 
 /*
diff --git a/lib/librte_eal/common/arch/ppc_64/rte_cpuflags.c b/lib/librte_eal/common/arch/ppc_64/rte_cpuflags.c
index 970a61c5e..e7a82452b 100644
--- a/lib/librte_eal/common/arch/ppc_64/rte_cpuflags.c
+++ b/lib/librte_eal/common/arch/ppc_64/rte_cpuflags.c
@@ -104,19 +104,8 @@ const struct feature_entry rte_cpu_feature_table[] = {
 static void
 rte_cpu_get_features(hwcap_registers_t out)
 {
-	int auxv_fd;
-	Elf64_auxv_t auxv;
-
-	auxv_fd = open("/proc/self/auxv", O_RDONLY);
-	assert(auxv_fd != -1);
-	while (read(auxv_fd, &auxv,
-		sizeof(Elf64_auxv_t)) == sizeof(Elf64_auxv_t)) {
-		if (auxv.a_type == AT_HWCAP)
-			out[REG_HWCAP] = auxv.a_un.a_val;
-		else if (auxv.a_type == AT_HWCAP2)
-			out[REG_HWCAP2] = auxv.a_un.a_val;
-	}
-	close(auxv_fd);
+	out[REG_HWCAP] = rte_cpu_getauxval(AT_HWCAP);
+	out[REG_HWCAP2] = rte_cpu_getauxval(AT_HWCAP2);
 }
 
 /*
diff --git a/lib/librte_eal/common/eal_common_cpuflags.c b/lib/librte_eal/common/eal_common_cpuflags.c
index 3a055f7c7..87c9539ad 100644
--- a/lib/librte_eal/common/eal_common_cpuflags.c
+++ b/lib/librte_eal/common/eal_common_cpuflags.c
@@ -2,11 +2,87 @@
  * Copyright(c) 2010-2014 Intel Corporation
  */
 
+#include <elf.h>
+#include <fcntl.h>
 #include <stdio.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#if defined(__GLIBC__) && defined(__GLIBC_PREREQ)
+#if __GLIBC_PREREQ(2, 16)
+#include <sys/auxv.h>
+#define HAS_AUXV 1
+#endif
+#endif
 
 #include <rte_common.h>
 #include <rte_cpuflags.h>
 
+#ifndef HAS_AUXV
+static unsigned long
+getauxval(unsigned long type)
+{
+	errno = ENOTSUP;
+	return 0;
+}
+#endif
+
+#if RTE_ARCH_64
+typedef Elf64_auxv_t Internal_Elfx_auxv_t;
+#else
+typedef Elf32_auxv_t Internal_Elfx_auxv_t;
+#endif
+
+
+/**
+ * Provides a method for retrieving values from the auxiliary vector and
+ * possibly running a string comparison.
+ */
+static unsigned long
+_rte_cpu_getauxval(unsigned long type, int cmp_str, const char *str)
+{
+	unsigned long val;
+
+	errno = 0;
+	val = getauxval(type);
+
+	if (!val && (errno == ENOTSUP || errno == ENOENT)) {
+		Internal_Elfx_auxv_t auxv;
+		int auxv_fd = open("/proc/self/auxv", O_RDONLY);
+
+		errno = ENOENT;
+		if (auxv_fd == -1)
+			return 0;
+
+		while (read(auxv_fd, &auxv, sizeof(auxv)) == sizeof(auxv)) {
+			if (auxv.a_type == type) {
+				errno = 0;
+				val = auxv.a_un.a_val;
+				if (cmp_str)
+					val = strcmp((const char *)val, str);
+				break;
+			}
+		}
+		close(auxv_fd);
+	}
+
+	return val;
+}
+
+unsigned long
+rte_cpu_getauxval(unsigned long type)
+{
+	return _rte_cpu_getauxval(type, 0, NULL);
+}
+
+int
+rte_cpu_strcmp_auxval(unsigned long type, const char *str)
+{
+	return _rte_cpu_getauxval(type, 1, str);
+}
+
 /**
  * Checks if the machine is adequate for running the binary. If it is not, the
  * program exits with status 1.
diff --git a/lib/librte_eal/common/include/generic/rte_cpuflags.h b/lib/librte_eal/common/include/generic/rte_cpuflags.h
index 8d31687d8..ffa3b744a 100644
--- a/lib/librte_eal/common/include/generic/rte_cpuflags.h
+++ b/lib/librte_eal/common/include/generic/rte_cpuflags.h
@@ -64,4 +64,17 @@ rte_cpu_check_supported(void);
 int
 rte_cpu_is_supported(void);
 
+/**
+ * This function attempts to retrieve a value from the auxiliary vector.
+ */
+unsigned long
+rte_cpu_getauxval(unsigned long type);
+
+/**
+ * This function retrieves a value from the auxiliary vector, and compares it
+ * as a string.
+ */
+int
+rte_cpu_strcmp_auxval(unsigned long type, const char *str);
+
 #endif /* _RTE_CPUFLAGS_H_ */
-- 
2.14.3