On Thu, Jun 6, 2013 at 8:02 PM, Dave Martin <Dave.Martin@xxxxxxx> wrote:
>> +static int __attribute__((used)) __tegra_smc_stack[10];
>
> Use __used instead of using GCC attributes directly.
>
>> +
>> +/*
>> + * With EABI, subtype and arg already end up in r0, r1 and r2 as they are
>> + * function arguments, but we prefer to play safe here and explicitly move
>> + * these values into the expected registers anyway. mov instructions without
>> + * any side-effect are turned into nops by the assembler, which limits
>> + * overhead.
>> + */
>> +static void tegra_generic_smc(u32 type, u32 subtype, u32 arg)
>> +{
>> + asm volatile(
>> + ".arch_extension sec\n\t"
>> + "ldr r3, =__tegra_smc_stack\n\t"
>
> ldr= should be avoided in inline asm, because GCC can't guess it's size,
> and can't guarantee that the literal pool word is close enough to be
> addressable (though for small compilation units it's unlikely to be a
> problem).
With Russel's suggested changes this will go away, but that's good to
know anyway.
>> + "dsb\n\t"
>
> Can you explain what this DSB is for?
Just a safety measure to make sure all memory operations are done
before we enter the secure monitor. Is it unnecessary?
>> + "smc #0\n\t"
>> + "ldr r3, =__tegra_smc_stack\n\t"
>> + "ldmia r3, {r4-r12, lr}"
>> + :
>> + : [type] "r" (type),
>> + [subtype] "r" (subtype),
>> + [arg] "r" (arg)
>> + : "r0", "r1", "r2", "r3", "r4", "memory");
>
> If r5-r12 are not clobbered, why do you save and restore them?
The secure monitor might change them.
> In the ARM ABI, r12 is a caller-save register, so you probably
> don't need to save/restore that even if it is clobbered.
Right, thanks. Didn't know r12 could be used as a scratch register.
Alex.
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