Re: [PATCH] Work around for enabling CONFIG_CMDLINE on ppc64le

From: Akshay Adiga
Date: Tue Sep 27 2016 - 13:54:58 EST

Hi Michael,

Here is the link to the bug raised on launchpad.

On 09/23/2016 09:45 AM, Akshay Adiga wrote:
Hi Michael,

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

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.

On 09/22/2016 03:51 PM, Michael Ellerman wrote:
Akshay Adiga <akshay.adiga@xxxxxxxxxxxxxxxxxx> writes:

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.

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
+ 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?