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SubjectRe: [PATCH] Work around for enabling CONFIG_CMDLINE on ppc64le
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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 <akshay.adiga@linux.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
>

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