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, 9 insertions, 0 deletions

diff --git a/litmus/Kconfig b/litmus/Kconfig
index 1c0a96d54992..f3aa7478faf7 100644
--- a/litmus/Kconfig
+++ b/litmus/Kconfig
@@ -80,6 +80,15 @@ config FEATHER_TRACE
           Feather-Trace basic tracing infrastructure. Includes device file
           driver and instrumentation point support.
 
+          There are actually two implementations of Feather-Trace.
+          1) A slower, but portable, default implementation.
+          2) Architecture-specific implementations that rewrite kernel .text at runtime.
+
+          If enabled, Feather-Trace will be based on 2) if available (currently only for x86).
+          However, if DEBUG_RODATA=y, then Feather-Trace will choose option 1) in any case
+          to avoid problems with write-protected .text pages.
+
+          Bottom line: to avoid increased overheads, choose DEBUG_RODATA=n.
 
 config SCHED_TASK_TRACE
         bool "Trace real-time tasks"