[Qemu-devel] [PATCH 1/6] osdep: Create qemu_getauxval and qemu_init_auxval

[Richard Henderson <rth@twiddle.net>]

Abstract away dependence on a system implementation of getauxval.

Signed-off-by: Richard Henderson <rth@twiddle.net>
---
 include/qemu/osdep.h | 20 ++++++++++++
 linux-user/main.c    |  1 +
 util/Makefile.objs   |  1 +
 util/getauxval.c     | 91 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 vl.c                 |  1 +
 5 files changed, 114 insertions(+)
 create mode 100644 util/getauxval.c

diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index 26136f1..8d1948b 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -215,4 +215,24 @@ bool fips_get_state(void);
  */
 char *qemu_get_local_state_pathname(const char *relative_pathname);
 
+/* Return a value for an AT_* type in the auxiliary vector.  Return 0 if the
+ * key is not present.  We attempt to emulate AT_HWCAP and AT_PLATFORM as
+ * best we can when real host support is not present.
+ */
+#ifdef _WIN32
+static inline unsigned long qemu_getauxval(unsigned long type) { return 0; }
+#else
+unsigned long qemu_getauxval(unsigned long type);
+#endif
+
+/* If supported and required, locate the auxiliary vector at program startup.
+ *
+ * @envp must be the third argument to main.
+ */
+#if defined(CONFIG_GETAUXVAL) || defined(_WIN32)
+static inline void qemu_init_auxval(char **envp) { }
+#else
+void qemu_init_auxval(char **envp);
+#endif
+
 #endif
diff --git a/linux-user/main.c b/linux-user/main.c
index 03859bc..fae102a 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -3549,6 +3549,7 @@ int main(int argc, char **argv, char **envp)
 
     module_call_init(MODULE_INIT_QOM);
 
+    qemu_init_auxval(envp);
     qemu_cache_utils_init(envp);
 
     if ((envlist = envlist_create()) == NULL) {
diff --git a/util/Makefile.objs b/util/Makefile.objs
index dc72ab0..8e0c929 100644
--- a/util/Makefile.objs
+++ b/util/Makefile.objs
@@ -11,3 +11,4 @@ util-obj-y += iov.o aes.o qemu-config.o qemu-sockets.o uri.o notify.o
 util-obj-y += qemu-option.o qemu-progress.o
 util-obj-y += hexdump.o
 util-obj-y += crc32c.o
+util-obj-y += getauxval.o
diff --git a/util/getauxval.c b/util/getauxval.c
new file mode 100644
index 0000000..55b639c
--- /dev/null
+++ b/util/getauxval.c
@@ -0,0 +1,91 @@
+/*
+ * QEMU access to the auxiliary vector
+ *
+ * Copyright (C) 2013 Red Hat, Inc
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "qemu-common.h"
+#include "qemu/osdep.h"
+
+#ifdef CONFIG_GETAUXVAL
+/* Don't inline this in qemu/osdep.h, because pulling in <sys/auxv.h> for
+   the system declaration of getauxval pulls in the system <elf.h>, which
+   conflicts with qemu's version.  */
+
+#include <sys/auxv.h>
+
+unsigned long qemu_getauxval(unsigned long key)
+{
+    return getauxval(key);
+}
+#elif !defined(_WIN32)
+#include "elf.h"
+
+/* Our elf.h doesn't contain Elf32_auxv_t and Elf64_auxv_t, which is ok because
+   that just makes it easier to define it properly for the host here.  */
+typedef struct {
+    unsigned long a_type;
+    unsigned long a_val;
+} ElfW_auxv_t;
+
+static const ElfW_auxv_t *auxv;
+
+void qemu_init_auxval(char **envp)
+{
+#ifdef __linux__
+    /* The auxiliary vector is located just beyond the initial environment.  */
+    while (*envp != NULL)
+        continue;
+    auxv = (const ElfW_auxv_t *)envp;
+#endif
+}
+
+static const char *default_platform(void)
+{
+    return NULL;
+}
+
+static unsigned long default_hwcap(void)
+{
+    return 0;
+}
+
+unsigned long qemu_getauxval(unsigned long type)
+{
+    /* If we were able to find the auxiliary vector, use it.  */
+    if (auxv) {
+        const ElfW_auxv_t *a;
+        for (a = auxv; a->a_type != 0; a++) {
+            if (a->a_type == type) {
+                return a->a_val;
+            }
+        }
+    }
+
+    /* Otherwise, guess defaults for the host based on compiler flags.  */
+    if (type == AT_HWCAP) {
+        return default_hwcap();
+    } else if (type == AT_PLATFORM) {
+        return (unsigned long)default_platform();
+    }
+    return 0;
+}
+#endif
diff --git a/vl.c b/vl.c
index f422a1c..c539fd3 100644
--- a/vl.c
+++ b/vl.c
@@ -2967,6 +2967,7 @@ int main(int argc, char **argv, char **envp)
     init_clocks();
     rtc_clock = host_clock;
 
+    qemu_init_auxval(envp);
     qemu_cache_utils_init(envp);
 
     QLIST_INIT (&vm_change_state_head);
-- 
1.8.1.4