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SubjectRe: arm64 -- psci tell the compiler in which registers we are expecting arguments
Hi Andy,

Thanks for the patch.

On Fri, Jan 23, 2015 at 05:31:54PM +0000, Andy Whitcroft wrote:
> When compiling the kernel with very recent gcc-4.9 compilers we see the
> following errors:
>
> /tmp/ccEayz7S.s: Assembler messages:
> /tmp/ccEayz7S.s:41: Error: .err encountered
> /tmp/ccEayz7S.s:42: Error: .err encountered
> /tmp/ccEayz7S.s:43: Error: .err encountered
> /tmp/ccEayz7S.s:101: Error: .err encountered
> /tmp/ccEayz7S.s:102: Error: .err encountered
> /tmp/ccEayz7S.s:103: Error: .err encountered
>
> This is due to assumptions about the register assignments made by gcc on
> function entry. The errors above occur when these assignments are not
> as expected. It turns out that when you enable mcount preables (-pg)
> these are altered and the compilation failed.
>
> Inform the compiler of these register requirements.
>
> BugLink: http://bugs.launchpad.net/bugs/1414002
> Signed-off-by: Andy Whitcroft <apw@canonical.com>
> ---
> arch/arm64/kernel/psci.c | 18 ++++++++++++++----
> 1 file changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/kernel/psci.c b/arch/arm64/kernel/psci.c
> index f1dbca7..425cf78 100644
> --- a/arch/arm64/kernel/psci.c
> +++ b/arch/arm64/kernel/psci.c
> @@ -113,9 +113,14 @@ static void psci_power_state_unpack(u32 power_state,
> * The following two functions are invoked via the invoke_psci_fn pointer
> * and will not be inlined, allowing us to piggyback on the AAPCS.
> */
> -static noinline int __invoke_psci_fn_hvc(u64 function_id, u64 arg0, u64 arg1,
> - u64 arg2)
> +static noinline int __invoke_psci_fn_hvc(u64 _function_id, u64 _arg0,
> + u64 _arg1, u64 _arg2)
> {
> + register u64 function_id asm("x0") = _function_id;
> + register u64 arg0 asm("x1") = _arg0;
> + register u64 arg1 asm("x2") = _arg1;
> + register u64 arg2 asm("x3") = _arg2;
> +

Given that we've already been bitten by the compiler, I think we should
just bite the bullet and implement these two functions in assembly in a
separate file rather than rely on register variables doing what we want.

Will


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