linux-kernel - Re: [PATCH] Work around for enabling CONFIG

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Date:   Thu, 22 Sep 2016 20:21:29 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Akshay Adiga <akshay.adiga@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Cc:     anton@...ba.org, Akshay Adiga <akshay.adiga@...ux.vnet.ibm.com>
Subject: Re: [PATCH] Work around for enabling CONFIG_CMDLINE on ppc64le

Akshay Adiga <akshay.adiga@...ux.vnet.ibm.com> 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
> +#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