Fix HelloWorld attach test for Linux kernels with ptrace ancestor lockdown.

Similar to a recent test I fixed for gdb-remote attach scenarios, this
fix is for Linux kernels, such as Ubuntu's stock setup on 11.04-ish and
later, where ptrace starts requiring a ptracer to be an ancestor of the
inferior to be ptraced.  This change checks for Linux and the ptrace-related
flags.  If they're found, it tries to switch on the "allow any ptracer" mode
for the inferior as the first statements in the program.  It's a best-effort
solution - if the prctl call fails, the failure is ignored, and probably will
lead to the test failing.

The ptrace security behavior can be modified system-wide, but is outside the
scope of the test to address.  Hence I went with this particular solution.

llvm-svn: 220650

1 files changed, 20 insertions, 0 deletions

diff --git a/lldb/test/python_api/hello_world/main.c b/lldb/test/python_api/hello_world/main.c
index dffc8c77b04..31a041ede74 100644
--- a/lldb/test/python_api/hello_world/main.c
+++ b/lldb/test/python_api/hello_world/main.c
@@ -1,6 +1,26 @@
 #include <stdio.h>
 
+#if defined(__linux__)
+#include <sys/prctl.h>
+#endif
+
 int main(int argc, char const *argv[]) {
+
+#if defined(__linux__)
+    // Immediately enable any ptracer so that we can allow the stub attach
+    // operation to succeed.  Some Linux kernels are locked down so that
+    // only an ancestor process can be a ptracer of a process.  This disables that
+    // restriction.  Without it, attach-related stub tests will fail.
+#if defined(PR_SET_PTRACER) && defined(PR_SET_PTRACER_ANY)
+    int prctl_result;
+
+    // For now we execute on best effort basis.  If this fails for
+    // some reason, so be it.
+    prctl_result = prctl(PR_SET_PTRACER, PR_SET_PTRACER_ANY, 0, 0, 0);
+    (void) prctl_result;
+#endif
+#endif
+
     printf("Hello world.\n"); // Set break point at this line.
     if (argc == 1)
         return 0;