Make platform-specific Feather-Trace depend on !CONFIG_DEBUG_RODATA

Feather-Trace rewrites instructions in the kernel's .text segment.
This segment may be write-protected if CONFIG_DEBUG_RODATA is selected.
In this case, fall back to the default flag-based Feather-Trace
implementation. In the future, we could either adopt the ftrace method
of rewriting .text addresses using non-.text mappings or we could
consider replacing Feather-Trace with ftrace altogether.

For now, this patch avoids unexpected runtime errors.

1 files changed, 13 insertions, 1 deletions

diff --git a/include/litmus/feather_trace.h b/include/litmus/feather_trace.h
index f3bbfa0935ef..028dfb206fb0 100644
--- a/include/litmus/feather_trace.h
+++ b/include/litmus/feather_trace.h
@@ -19,7 +19,12 @@ static inline int fetch_and_dec(int *val)
         return atomic_sub_return(1, (atomic_t*) val) + 1;
 }
 
-#ifdef CONFIG_ARCH_HAS_FEATHER_TRACE
+/* Don't use rewriting implementation if kernel text pages are read-only.
+ * Ftrace gets around this by using the identity mapping, but that's more
+ * effort that is warrented right now for Feather-Trace.
+ * Eventually, it may make sense to replace Feather-Trace with ftrace.
+ */
+#if defined(CONFIG_ARCH_HAS_FEATHER_TRACE) && !defined(CONFIG_DEBUG_RODATA)
 
 #include <asm/feather_trace.h>
 
@@ -27,6 +32,13 @@ static inline int fetch_and_dec(int *val)
 
 /* provide default implementation */
 
+#include <asm/timex.h> /* for get_cycles() */
+
+static inline unsigned long long ft_timestamp(void)
+{
+        return get_cycles();
+}
+
 #define feather_callback
 
 #define MAX_EVENTS 1024