Android-specific prctl

[enh]

Android kernels have an extra prctl that lets us set a name for an
anonymous VMA, which is useful for debugging. at the moment strace
shows it like this:

prctl(0x53564d41 /* PR_??? */, 0, 0x7f7ab0e000, 0x2000, 0x7f7aaf76d0) = 0
prctl(0x53564d41 /* PR_??? */, 0, 0x7f7ab0d000, 0x1000, 0x7f7aaf76e8) = 0

with this patch:

diff --git a/prctl.c b/prctl.c
index 4a6bd25..e43569c 100644
--- a/prctl.c
+++ b/prctl.c
@@ -94,6 +94,22 @@ prctl_enter(struct tcb *tcp)
 		printstr(tcp, tcp->u_arg[1], TASK_COMM_LEN);
 		break;

+#define PR_SET_VMA   0x53564d41
+#define PR_SET_VMA_ANON_NAME    0
+	case PR_SET_VMA:
+		if (tcp->u_arg[1] == PR_SET_VMA_ANON_NAME) {
+			tprintf(", %lu", tcp->u_arg[1]);
+			tprintf(", %#lx", tcp->u_arg[2]);
+			tprintf(", %lu, ", tcp->u_arg[3]);
+			printstr(tcp, tcp->u_arg[4], -1);
+		} else {
+			// There are no other sub-options now, but there
+			// might be in future...
+			for (i = 1; i < tcp->s_ent->nargs; i++)
+				tprintf(", %#lx", tcp->u_arg[i]);
+		}
+		break;
+
 	case PR_SET_MM:
 		tprints(", ");
 		printxval(pr_set_mm, tcp->u_arg[1], "PR_SET_MM_???");

we get this instead:

prctl(0x53564d41 /* PR_??? */, 0, 0x7f7ffe0000, 8192, "thread signal stack") = 0
prctl(0x53564d41 /* PR_??? */, 0, 0x7f7ffdf000, 4096, "thread signal
stack guard page") = 0

obviously i could change the xlat prctl_options.in file to add
PR_SET_VMA, but this isn't in upstream kernels so that seems wrong.

i can easily keep the patch above and/or the one that touches the xlat
file in our tree, but i thought i'd ask what -- if anything -- of this
you'd be interested in having in upstream strace.

-- 
Elliott Hughes - http://who/enh - http://jessies.org/~enh/
Android native code/tools questions? Mail me/drop by/add me as a reviewer.