linux-user: Allow targets to specify a minimum uname release

For newer target architectures, glibc can be picky about the kernel
version: for example, it will not run on an aarch64 system unless
the kernel reports itself as at least 3.8.0. Accommodate this by
enhancing the existing support for faking the kernel version so
that each target can optionally specify a minimum version: if
the user doesn't force a specific fake version then we will override
with the minimum required version only if the real host kernel
version is insufficient.

Use this facility to let aarch64 report a minimum of 3.8.0.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1378235544-22290-21-git-send-email-peter.maydell@linaro.org

linux-user/main.c

@@ -3676,6 +3676,8 @@ int main(int argc, char **argv, char **envp)
     /* Scan interp_prefix dir for replacement files. */
     init_paths(interp_prefix);
 
+    init_qemu_uname_release();
+
     if (cpu_model == NULL) {
 #if defined(TARGET_I386)
 #ifdef TARGET_X86_64

linux-user/qemu.h

@@ -197,6 +197,7 @@ extern THREAD CPUState *thread_cpu;
 void cpu_loop(CPUArchState *env);
 char *target_strerror(int err);
 int get_osversion(void);
+void init_qemu_uname_release(void);
 void fork_start(void);
 void fork_end(int child);
 

linux-user/syscall.c

@@ -4863,21 +4863,13 @@ int host_to_target_waitstatus(int status)
     return status;
 }
 
-int get_osversion(void)
+static int relstr_to_int(const char *s)
 {
-    static int osversion;
-    struct new_utsname buf;
-    const char *s;
+    /* Convert a uname release string like "2.6.18" to an integer
+     * of the form 0x020612. (Beware that 0x020612 is *not* 2.6.12.)
+     */
     int i, n, tmp;
-    if (osversion)
-        return osversion;
-    if (qemu_uname_release && *qemu_uname_release) {
-        s = qemu_uname_release;
-    } else {
-        if (sys_uname(&buf))
-            return 0;
-        s = buf.release;
-    }
+
     tmp = 0;
     for (i = 0; i < 3; i++) {
         n = 0;
@@ -4887,13 +4879,55 @@ int get_osversion(void)
             s++;
         }
         tmp = (tmp << 8) + n;
-        if (*s == '.')
+        if (*s == '.') {
             s++;
         }
-    osversion = tmp;
+    }
+    return tmp;
+}
+
+int get_osversion(void)
+{
+    static int osversion;
+    struct new_utsname buf;
+    const char *s;
+
+    if (osversion)
+        return osversion;
+    if (qemu_uname_release && *qemu_uname_release) {
+        s = qemu_uname_release;
+    } else {
+        if (sys_uname(&buf))
+            return 0;
+        s = buf.release;
+    }
+    osversion = relstr_to_int(s);
     return osversion;
 }
 
+void init_qemu_uname_release(void)
+{
+    /* Initialize qemu_uname_release for later use.
+     * If the host kernel is too old and the user hasn't asked for
+     * a specific fake version number, we might want to fake a minimum
+     * target kernel version.
+     */
+#ifdef UNAME_MINIMUM_RELEASE
+    struct new_utsname buf;
+
+    if (qemu_uname_release && *qemu_uname_release) {
+        return;
+    }
+
+    if (sys_uname(&buf)) {
+        return;
+    }
+
+    if (relstr_to_int(buf.release) < relstr_to_int(UNAME_MINIMUM_RELEASE)) {
+        qemu_uname_release = UNAME_MINIMUM_RELEASE;
+    }
+#endif
+}
 
 static int open_self_maps(void *cpu_env, int fd)
 {