commit ffb40c659a690f4341e43051f6d5114732b3fe46
Author: Frank Ch. Eigler <fche@redhat.com>
Date:   Thu Mar 5 07:17:04 2020 -0500

    RHBZ1810216: fix ftrace() tapset function related autoconf test
    
    It was reported that the ftrace() tapset function stopped working at
    some point - due to an autoconf-* false negative.  We failed to notice
    because the tapset function was quietly mapped to a nop in this case.
    Now ftrace() will #error in -p4 if autoconf doesn't detect a suitable
    kernel facility.  A forked testcase buildok/logging-embedded2.stp
    checks for it.
    
    Suggested-by: Oleksandr Natalenko <onatalen@redhat.com>

diff --git a/runtime/linux/autoconf-trace-printk.c b/runtime/linux/autoconf-trace-printk.c
index 8330a58..c7515bc 100644
--- a/runtime/linux/autoconf-trace-printk.c
+++ b/runtime/linux/autoconf-trace-printk.c
@@ -1,4 +1,5 @@
 #include <linux/kernel.h>
+#include <linux/string.h>
 
 int bar (void) {
   static char *fmt = "%s\n";
diff --git a/tapset/linux/logging.stp b/tapset/linux/logging.stp
index 6192cf6..b13b5cc 100644
--- a/tapset/linux/logging.stp
+++ b/tapset/linux/logging.stp
@@ -25,6 +25,8 @@ function ftrace (msg:string) %{ /* unmodified-fnargs */
        to defeat trace_printk -> __trace_bprintk optimization.  That's
        because bprintk doesn't save the incoming strings, only their
        addresses. */
+#else
+  #error "trace_printk not supported"
 #endif
 %}
 
diff --git a/testsuite/buildok/logging-embedded.stp b/testsuite/buildok/logging-embedded.stp
index c97bd5a..7e2f15d 100755
--- a/testsuite/buildok/logging-embedded.stp
+++ b/testsuite/buildok/logging-embedded.stp
@@ -8,6 +8,6 @@ probe begin {
       exit()
       error("error")
       stp_print_binary(1, 0, 0, 0, 0)
-      ftrace("ftrace")
+      // ftrace() tested in logging-embedded2.stp
       printk(0,"Zoink!  The paper tape punch is burning chads!")
 }
diff --git a/testsuite/buildok/logging-embedded2.stp b/testsuite/buildok/logging-embedded2.stp
new file mode 100755
index 0000000..528d5d0
--- /dev/null
+++ b/testsuite/buildok/logging-embedded2.stp
@@ -0,0 +1,7 @@
+#! stap -gp4
+
+// build-test the logging tapset functions - ftrace() only usable if STAPCONF detects it
+
+probe begin {
+      ftrace("ftrace")
+}