Better get_stackid rewriter logic and unittest version testing

Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>

src/cc/frontends/clang/b_frontend_action.cc

@@ -315,6 +315,8 @@ bool BTypeVisitor::VisitCallExpr(CallExpr *Call) {
         string prefix, suffix;
         string map_update_policy = "BPF_ANY";
         string txt;
+        auto rewrite_start = Call->getLocStart();
+        auto rewrite_end = Call->getLocEnd();
         if (memb_name == "lookup_or_init") {
           map_update_policy = "BPF_NOEXIST";
           string name = Ref->getDecl()->getName();
@@ -354,8 +356,11 @@ bool BTypeVisitor::VisitCallExpr(CallExpr *Call) {
           txt += ", bpf_get_smp_processor_id(), " + args_other + ")";
         } else if (memb_name == "get_stackid") {
             if (table_it->type == BPF_MAP_TYPE_STACK_TRACE) {
+              string arg0 = rewriter_.getRewrittenText(SourceRange(Call->getArg(0)->getLocStart(),
+                                                                   Call->getArg(0)->getLocEnd()));
               txt = "bpf_get_stackid(";
-              txt += "bpf_pseudo_fd(1, " + fd + "), " + args + ")";
+              txt += "bpf_pseudo_fd(1, " + fd + "), " + arg0;
+              rewrite_end = Call->getArg(0)->getLocEnd();
             } else {
               unsigned diag_id = C.getDiagnostics().getCustomDiagID(DiagnosticsEngine::Error,
                                                                     "get_stackid only available on stacktrace maps");
@@ -387,12 +392,12 @@ bool BTypeVisitor::VisitCallExpr(CallExpr *Call) {
 
           txt = prefix + args + suffix;
         }
-        if (!rewriter_.isRewritable(Call->getLocStart())) {
+        if (!rewriter_.isRewritable(rewrite_start) || !rewriter_.isRewritable(rewrite_end)) {
           C.getDiagnostics().Report(Call->getLocStart(), diag::err_expected)
               << "use of map function not in a macro";
           return false;
         }
-        rewriter_.ReplaceText(SourceRange(Call->getLocStart(), Call->getLocEnd()), txt);
+        rewriter_.ReplaceText(SourceRange(rewrite_start, rewrite_end), txt);
         return true;
       }
     }

tests/python/test_stackid.py

@@ -3,8 +3,23 @@
 # Licensed under the Apache License, Version 2.0 (the "License")
 
 import bcc
+import distutils.version
+import os
 import unittest
 
+def kernel_version_ge(major, minor):
+    # True if running kernel is >= X.Y
+    version = distutils.version.LooseVersion(os.uname()[2]).version
+    if version[0] > major:
+        return True
+    if version[0] < major:
+        return False
+    if minor and version[1] < minor:
+        return False
+    return True
+
+
+@unittest.skipUnless(kernel_version_ge(4,6), "requires kernel >= 4.6")
 class TestStackid(unittest.TestCase):
     def test_simple(self):
         b = bcc.BPF(text="""
@@ -14,7 +29,7 @@ BPF_STACK_TRACE(stack_traces, 10240);
 BPF_HASH(stack_entries, int, int);
 BPF_HASH(stub);
 int kprobe__htab_map_delete_elem(struct pt_regs *ctx, struct bpf_map *map, u64 *k) {
-    int id = stack_traces.get_stackid(ctx, (BPF_F_REUSE_STACKID));
+    int id = stack_traces.get_stackid(ctx, BPF_F_REUSE_STACKID);
     if (id < 0)
         return 0;
     int key = 1;