On Fri, 5 Feb 2016 15:05:17 +0100
Petr Mladek [off-list ref] wrote:

On Mon 2016-01-25 16:29:54, Torsten Duwe wrote:

quoted

diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c
index ef8b916..29b7014 100644
--- a/arch/powerpc/kernel/ftrace.c
+++ b/arch/powerpc/kernel/ftrace.c

@@ -28,6 +28,11 @@
 
 
 #ifdef CONFIG_DYNAMIC_FTRACE
+#if defined(CONFIG_DYNAMIC_FTRACE_WITH_REGS) && defined(CONFIG_PPC64) && \
+  !defined(CC_USING_MPROFILE_KERNEL)
+#error "DYNAMIC_FTRACE_WITH_REGS requires working -mprofile-kernel"
+#endif  

CONFIG_DYNAMIC_FTRACE_WITH_REGS is automatically enabled when
both CONFIG_DYNAMIC_FTRACE and HAVE_DYNAMIC_FTRACE_WITH_REGS
are enabled.

Therefore it is not possible to build kernel with broken gcc
and DYNAMIC_FTRACE.

IMHO, we need to allow to explicitely disable DYNAMIC_FTRACE_WITH_REGS
if the compiler is broken to get around this build error.

We either need to define DYNAMIC_FTRACE_WITH_REGS as a proper
bool with description, help text, ... Or we need a way to
explicitely disable HAVE_DYNAMIC_FTRACE_WITH_REGS. Or something
like this.

You mean something like this?

(not tested)

-- Steve

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index e45db6b0d878..19377bacebfc 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig

@@ -470,6 +470,19 @@ config DYNAMIC_FTRACE_WITH_REGS
 	def_bool y
 	depends on DYNAMIC_FTRACE
 	depends on HAVE_DYNAMIC_FTRACE_WITH_REGS
+	depends on !DISABLE_DYNAMIC_FTRACE_WITH_REGS
+
+config DISABLE_DYNAMIC_FTRACE_WITH_REGS
+       bool "Force build to not have function tracer pass in registers"
+       depends on DYNAMIC_FTRACE
+       depends on HAVE_DYNAMIC_FTRACE_WITH_REGS
+       help
+	 If the architecture supports passing in registers to the function
+	 tracer, then that is automatically enabled. But there may be some
+	 compilers out there that are broken and cause this to fail.
+	 This option makes the build think that the architecture does not
+	 support the register passing and allows the build to work even
+	 with compilers that do not support the feature.g
 
 config FUNCTION_PROFILER
 	bool "Kernel function profiler"