Hi Michael,

Anton found this bug and raised it against gcc v7.0 and a fix is available
  in upstream gcc.

	https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71709

Currently, gcc v5.4.0  and v6.1.1 shipped with Ubuntu 16.04 and 16.10  respectively,
  are hitting this problem.

I have also raised bug against Ubuntu for fixing gcc for 16.04.

https://bugzilla.linux.ibm.com/show_bug.cgi?id=146668


On 09/22/2016 03:51 PM, Michael Ellerman wrote:

Akshay Adiga [off-list ref] writes:

quoted

Observed that boot arguments (passed as CONFIG_CMDLINE)  are not being
picked up by kernel while using gcc-ppc64-linux-gnu v5.4.0 and v6.1.1.
While it works as expected with v5.3.1 .

Found that in init/main.c in  setup_command_line() the pointers passed to
strcpy() is messed up.

Hi Akshay,

Thanks for debugging this.

quoted

The problem goes away when compiler optimization is restricted to -O1.

diff --git a/init/main.c b/init/main.c
index a8a58e2..4259c42 100644
--- a/init/main.c
+++ b/init/main.c

@@ -358,7 +358,13 @@ static inline void smp_prepare_cpus(unsigned int maxcpus) { }
   * parsing is performed in place, and we should allow a component to
   * store reference of name/value for future reference.
   */
-static void __init setup_command_line(char *command_line)
+static void __init
+#ifdef CONFIG_PPC64
+	#if  GCC_VERSION > 50301
+		__attribute__((optimize("-O1")))
+	#endif
+#endif
+		setup_command_line(char *command_line)
  {
  	saved_command_line =
  		memblock_virt_alloc(strlen(boot_command_line) + 1, 0);

But I can't merge that patch.

Our options are one or both of:
  - get GCC fixed and backport the fix to the compilers we care about.
  - blacklist the broken compiler versions.

Is there a GCC bug filed for this?

cheers