Re: [Xen-devel] [PATCH] arm32: fix build after 063188f4b3

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 10.10.14 at 16:12, <julien.grall@xxxxxxxxxx> wrote:
> On 10/10/2014 14:58, Jan Beulich wrote:
>> "xen: arm: Add support for the Exynos secure firmware" introduced code
>> assuming that exynos_smc() would get called with arguments in certain
>> registers. While the "noinline" attribute guarantees the function to
>> not get inlined, it does not guarantee that all arguments arrive in the
>> assumed registers: gcc's interprocedural analysis can result in clone
>> functions to be created where some of the incoming arguments (commonly
>> when they have constant values) get replaced by putting in place the
>> respective values inside the clone.
> 
> I'm not sure to understand here. If the function is marked as noinlined, 
> that would mean the arguments will be passed with the ARM in the 
> register with the ARM calling convention (i.e r0 for argument 0...). Why 
> GCC would try to create a clone of this function?

The compiler is free to do so as long as the language specification isn't
being violated.

>> The alternative of adding __attribute__((optimize("-fno-ipa-cp")))
>> to the function definition would likely not work with all supported
>> compiler versions.
> 
> The function was first introduced in arch/arm/psci.c (it's a copy of the 
> Linux one in arch/arm/kernel/psci.c).
> 
> Does it mean that Linux code is buggy too?

Likely.

> This function is duplicate in 3 different places in Xen:
>       - arch/arm/psci.c
>       - arch/platforms/exynos5.c
>       - arch/platforms/seattle.c
> 
> So all those functions should be fixed. I think it's time to introduce a 
> global SMC function...

Okay, I got the build failure only in this one place. But if and when
the compiler choses to do such transformations is entirely up to it,
so yes, if there are multiple instances likely they all would need
fixing.

Jan


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