[Qemu-devel] [PATCH v3 23/25] qemu/osdep: Remove the need for qemu_init_auxval

[Richard Henderson <rth@twiddle.net>]

Instead of getting backup auxv data from the env pointer given to main,
read it from /proc/self/auxv.  We can do this at any time, so we're not
tied to any ordering wrt a call to qemu_init_auxval from main.

Signed-off-by: Richard Henderson <rth@twiddle.net>
---
 include/qemu/osdep.h | 12 ------------
 linux-user/main.c    |  1 -
 util/getauxval.c     | 51 +++++++++++++++++++++++++++++++++++++++------------
 vl.c                 |  1 -
 4 files changed, 39 insertions(+), 26 deletions(-)

diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index ffb2966..483778d 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -237,18 +237,6 @@ unsigned long qemu_getauxval(unsigned long type);
 static inline unsigned long qemu_getauxval(unsigned long type) { return 0; }
 #endif
 
-/**
- * qemu_init_auxval:
- * @envp: the third argument to main
- *
- * If supported and required, locate the auxiliary vector at program startup.
- */
-#if defined(CONFIG_GETAUXVAL) || !defined(__linux__)
-static inline void qemu_init_auxval(char **envp) { }
-#else
-void qemu_init_auxval(char **envp);
-#endif
-
 void qemu_set_tty_echo(int fd, bool echo);
 
 #endif
diff --git a/linux-user/main.c b/linux-user/main.c
index a87c6f7..14b7b94 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -3829,7 +3829,6 @@ int main(int argc, char **argv, char **envp)
 
     module_call_init(MODULE_INIT_QOM);
 
-    qemu_init_auxval(envp);
     qemu_cache_utils_init();
 
     if ((envlist = envlist_create()) == NULL) {
diff --git a/util/getauxval.c b/util/getauxval.c
index 476c883..25f48e5 100644
--- a/util/getauxval.c
+++ b/util/getauxval.c
@@ -48,24 +48,51 @@ typedef struct {
 
 static const ElfW_auxv_t *auxv;
 
-void qemu_init_auxval(char **envp)
+static const ElfW_auxv_t *qemu_init_auxval(void)
 {
-    /* The auxiliary vector is located just beyond the initial environment.  */
-    while (*envp++ != NULL) {
-        continue;
+    ElfW_auxv_t *a;
+    ssize_t size = 512, r, ofs;
+    int fd;
+
+    /* Allocate some initial storage.  Make sure the first entry is set
+       to end-of-list, so that we've got a valid list in case of error.  */
+    auxv = a = g_malloc(size);
+    a[0].a_type = 0;
+    a[0].a_val = 0;
+
+    fd = open("/proc/self/auxv", O_RDONLY);
+    if (fd < 0) {
+        return a;
+    }
+
+    /* Read the first SIZE bytes.  Hopefully, this covers everything.  */
+    r = read(fd, a, size);
+
+    if (r == size) {
+        /* Continue to expand until we do get a partial read.  */
+        do {
+            ofs = size;
+            size *= 2;
+            auxv = a = g_realloc(a, size);
+            r = read(fd, (char *)a + ofs, ofs);
+        } while (r == ofs);
     }
-    auxv = (const ElfW_auxv_t *)envp;
+
+    close(fd);
+    return a;
 }
 
 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;
-            }
+    const ElfW_auxv_t *a = auxv;
+
+    if (unlikely(a == NULL)) {
+        a = qemu_init_auxval();
+    }
+
+    for (; a->a_type != 0; a++) {
+        if (a->a_type == type) {
+            return a->a_val;
         }
     }
 
diff --git a/vl.c b/vl.c
index be69c7f..256287e 100644
--- a/vl.c
+++ b/vl.c
@@ -3029,7 +3029,6 @@ int main(int argc, char **argv, char **envp)
 
     rtc_clock = QEMU_CLOCK_HOST;
 
-    qemu_init_auxval(envp);
     qemu_cache_utils_init();
 
     QLIST_INIT (&vm_change_state_head);
-- 
1.9.3