PR10702: preprocessor conditional for kernel CONFIG_foo

* session.h (kernel_config[]): New session field.
* main.cxx (parse_kernel_config): Populate it.
* parse.cxx (eval_comparison): Use it.
* testsuite/buildok/utrace.stp, testsuite/parseok/kconfig.stp: New tests.
* NEWS, stap.1.in, doc/langref.tex: Mention it.

8 files changed, 80 insertions, 7 deletions

diff --git a/NEWS b/NEWS
index b8a42305..9fe26ba6 100644
--- a/NEWS
+++ b/NEWS
@@ -1,5 +1,8 @@
 * What's new
 
+- Preprocessor conditional for kernel configuration testing:
+  %( CONFIG_foo == "y" %? ... %) 
+
 - ftrace(msg:string) tapset function to send strings to the system-wide
   ftrace ring-buffer (if any).
 
diff --git a/doc/langref.tex b/doc/langref.tex
index 523deb1b..3afe6128 100644
--- a/doc/langref.tex
+++ b/doc/langref.tex
@@ -1816,6 +1816,17 @@ probe kernel.function (
 %( arch == "ia64" %?
     probe syscall.vliw = kernel.function("vliw_widget") {}
 %)
+
+\end{verbatim}
+\end{vindent}
+
+The following code adapts to the presence of a kernel CONFIG option.
+
+\begin{vindent}
+\begin{verbatim}
+%( CONFIG_UTRACE == "y" %?
+    probe process.syscall {}
+%)
 \end{verbatim}
 \end{vindent}
 
diff --git a/main.cxx b/main.cxx
index 86990675..c0ff3ba5 100644
--- a/main.cxx
+++ b/main.cxx
@@ -335,8 +335,8 @@ setup_signals (sighandler_t handler)
   sigaction (SIGTERM, &sa, NULL);
 }
 
-void
-setup_kernel_release (systemtap_session &s, const char* kstr) {
+void setup_kernel_release (systemtap_session &s, const char* kstr) 
+{
     if (kstr[0] == '/') // fully specified path
       {
         s.kernel_build_tree = kstr;
@@ -364,6 +364,29 @@ setup_kernel_release (systemtap_session &s, const char* kstr) {
       }
 }
 
+
+void parse_kernel_config (systemtap_session &s) 
+{
+  // PR10702: pull config options
+  string kernel_config_file = s.kernel_build_tree + "/.config";
+  ifstream kcf (kernel_config_file.c_str());
+  string line;
+  while (getline (kcf, line))
+    {
+      if (line.substr(0, 7) != "CONFIG_") continue;
+      size_t off = line.find('=');
+      if (off == string::npos) continue;
+      string key = line.substr(0, off);
+      string value = line.substr(off+1, string::npos);
+      s.kernel_config[key] = value;
+    }
+  if (s.verbose > 2)
+    clog << "Parsed kernel \"" << kernel_config_file << "\", number of tuples: " << s.kernel_config.size() << endl;
+  
+  kcf.close();
+}
+
+
 static void
 checkOptions (systemtap_session &s)
 {
@@ -945,6 +968,9 @@ main (int argc, char * const argv [])
       clog << "Created temporary directory \"" << s.tmpdir << "\"" << endl;
   }
 
+  // Now that no further changes to s.kernel_build_tree can occur, let's use it.
+  parse_kernel_config (s);
+
   // Create the name of the C source file within the temporary
   // directory.
   s.translated_source = string(s.tmpdir) + "/" + s.module_name + ".c";
@@ -1028,7 +1054,7 @@ main (int argc, char * const argv [])
           // GLOB_NOMATCH is acceptable
 
           if (s.verbose>1 && globbuf.gl_pathc > 0)
-            clog << "Searched '" << dir << "', "
+            clog << "Searched \"" << dir << "\", "
                  << "found " << globbuf.gl_pathc << endl;
 
           for (unsigned j=0; j<globbuf.gl_pathc; j++)
diff --git a/parse.cxx b/parse.cxx
index bfd7600f..b88ef7ff 100644
--- a/parse.cxx
+++ b/parse.cxx
@@ -183,12 +183,14 @@ bool eval_comparison (const OPERAND& lhs, const token* op, const OPERAND& rhs)
 // The basic form is %( CONDITION %? THEN-TOKENS %: ELSE-TOKENS %)
 // where CONDITION is: kernel_v[r] COMPARISON-OP "version-string"
 //                 or: arch COMPARISON-OP "arch-string"
+//                 or: CONFIG_foo COMPARISON-OP "config-string"
 //                 or: "string1" COMPARISON-OP "string2"
 //                 or: number1 COMPARISON-OP number2
 // The %: ELSE-TOKENS part is optional.
 //
 // e.g. %( kernel_v > "2.5" %? "foo" %: "baz" %)
 // e.g. %( arch != "i?86" %? "foo" %: "baz" %)
+// e.g. %( CONFIG_foo %? "foo" %: "baz" %)
 //
 // Up to an entire %( ... %) expression is processed by a single call
 // to this function.  Tokens included by any nested conditions are
@@ -270,6 +272,23 @@ bool eval_pp_conditional (systemtap_session& s,
 
       return result;
     }
+  else if (l->type == tok_identifier && l->content.substr(0,7) == "CONFIG_" && r->type == tok_string)
+    {
+      string lhs = s.kernel_config[l->content]; // may be empty
+      string rhs = r->content;
+
+      int nomatch = fnmatch (lhs.c_str(), rhs.c_str(), FNM_NOESCAPE); // still spooky
+
+      bool result;
+      if (op->type == tok_operator && op->content == "==")
+        result = !nomatch;
+      else if (op->type == tok_operator && op->content == "!=")
+        result = nomatch;
+      else
+        throw parse_error ("expected '==' or '!='", op);
+
+      return result;
+    }
   else if (l->type == tok_string && r->type == tok_string)
     {
       string lhs = l->content;
@@ -291,10 +310,8 @@ bool eval_pp_conditional (systemtap_session& s,
 	    && op->type == tok_operator)
     throw parse_error ("expected number literal as right value", r);
 
-  // XXX: support other forms?  "CONFIG_SMP" ?
-
   else
-    throw parse_error ("expected 'arch' or 'kernel_v' or 'kernel_vr'\n"
+    throw parse_error ("expected 'arch' or 'kernel_v' or 'kernel_vr' or 'CONFIG_...'\n"
 		       "             or comparison between strings or integers", l);
 }
 
diff --git a/session.h b/session.h
index a2176793..cc13c321 100644
--- a/session.h
+++ b/session.h
@@ -87,6 +87,7 @@ struct systemtap_session
   std::string kernel_release;
   std::string kernel_base_release;
   std::string kernel_build_tree;
+  std::map<std::string,std::string> kernel_config;
   std::string architecture;
   std::string runtime_path;
   std::string data_path;
diff --git a/stap.1.in b/stap.1.in
index e6370dfc..b6f79fe9 100644
--- a/stap.1.in
+++ b/stap.1.in
@@ -340,12 +340,21 @@ by
 If, on the other hand, the first part is the identifier
 .BR arch
 to refer to the processor architecture (as named by the kernel
-build system ARCH/SUBARCH), then the second part then the second
+build system ARCH/SUBARCH), then the second  
 part is one of the two string comparison operators
 .BR == " or " != ,
 and the third part is a string literal for matching it.  This
 comparison is a wildcard (mis)match.
 .PP
+Similarly, if the first part is an identifier like
+.BR CONFIG_something
+to refer to a kernel configuration option, then the second part is
+.BR == " or " != ,
+and the third part is a string literal for matching the value
+(commonly "y" or "m").  Nonexistent or unset kernel configuration
+options are represented by the empty string.  This comparison is also
+a wildcard (mis)match.
+.PP
 Otherwise, the CONDITION is expected to be a comparison between two string
 literals or two numeric literals.  In this case, the arguments are the only
 variables usable.
diff --git a/testsuite/buildok/utrace.stp b/testsuite/buildok/utrace.stp
new file mode 100755
index 00000000..436bf9c4
--- /dev/null
+++ b/testsuite/buildok/utrace.stp
@@ -0,0 +1,3 @@
+#! stap -p4
+
+probe   %( CONFIG_UTRACE == "y" %? process.begin %: never %)    { }
diff --git a/testsuite/parseok/kconfig.stp b/testsuite/parseok/kconfig.stp
new file mode 100755
index 00000000..02920853
--- /dev/null
+++ b/testsuite/parseok/kconfig.stp
@@ -0,0 +1,3 @@
+#! stap -p2
+
+%( CONFIG_NO_SUCH_CONFIG == "" %? probe never {} %: %)