use C shim to start Android app

This should avoid relying on features of the Android builtin shell,
and so hopefully avoid failures like this one
http://git-annex.branchable.com/design/assistant/blog/day_197__template_haskell/#comment-07f90830f78f6495dcbdf90eb8636129

The C shim sets up busybox, and uses its builtin shell to run runshell.

It's important that busybox be configured with
CONFIG_FEATURE_SH_STANDALONE, so that while runshell is running, it
does not rely on either system utilities, or busybox being already
installed.

1 files changed, 52 insertions, 0 deletions

diff --git a/standalone/android/start.c b/standalone/android/start.c
new file mode 100644
index 000000000..1f54ba259
--- /dev/null
+++ b/standalone/android/start.c
@@ -0,0 +1,52 @@
+/* Installed as lib.start.so, this bootstraps a working busybox and uses
+ * it to run lib.runshell.so. */
+
+#include <unistd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+
+void chopdir (char *s) {
+	char *p=strrchr(s, '/');
+	if (p == NULL) {
+		fprintf(stderr, "cannot find directory in %s", s);
+		exit(1);
+	}
+	p[0] = '\0';
+}
+
+main () {
+	char buf[1024];
+	char *p;
+	struct stat st_buf;
+
+	/* Get something like /data/data/ga.androidterm/lib/lib.start.so */
+	int n=readlink("/proc/self/exe", buf, 1023);
+	if (n < 1) {
+		fprintf(stderr, "failed to find own name");
+		exit(1);
+	}
+	buf[n] = '\0';
+
+	/* Change directory to something like /data/data/ga.androidterm */
+	chopdir(buf);
+	chopdir(buf);
+	if (chdir(buf) != 0) {
+		perror("chdir");
+		exit(1);
+	}
+
+	/* If this is the first run, set up busybox link. */
+	if (stat("bin/busybox", &st_buf) != 0) {
+		mkdir("bin", 0777);
+		if (link("lib/lib.busybox.so", "bin/busybox") != 0) {
+			perror("link busybox");
+			exit(1);
+		}
+	}
+
+	execl("bin/busybox", "bin/busybox", "sh", "lib/lib.runshell.so", NULL);
+	perror("error running busybox sh");
+}