[PATCH 1/1 v2] ARM: Thumb-2: Symbol manipulation macros for function body copying

[Dave Martin]

On Thu, Jan 13, 2011 at 5:55 PM, Russell King - ARM Linux
<linux at arm.linux.org.uk> wrote:
> On Thu, Jan 13, 2011 at 02:51:45PM -0600, Dave Martin wrote:
>> +/* Cast function pointer to integer: */
>> +#define __funcp_to_uint(funcp) ({                            \
>
> uint is confusing here - it suggests casting a pointer to an unsigned int,
> rather than a uintptr_t.  Please use uintptr here.
>
>> +/*
>> + * FSYM_REBASE: Determine the correct function pointer for funcp,
>> + * after the function has been copied to dest_buf:
>> + */
>> +#define FSYM_REBASE(funcp, dest_buf)                                 \
>> +     __uint_to_funcp((uintptr_t)(dest_buf) | FSYM_TYPE(funcp), funcp)
>> +
>> +/*
>> + * FSYM_BASE: Determine the base address in memory of the function funcp
>> + * FSYM_TYPE: Determine the instruction set type (ARM/Thumb) of funcp
>> + * (both defined below)
>> + */
>> +
>> +#ifdef CONFIG_THUMB2_KERNEL
>> +#define FSYM_BASE(funcp) ((void *)(__funcp_to_uint(funcp) & ~(uintptr_t)1))
>> +#define FSYM_TYPE(funcp) (__funcp_to_uint(funcp) & 1)
>> +#else /* !CONFIG_THUMB2_KERNEL */
>> +#define FSYM_BASE(funcp) ((void *)__funcp_to_uint(funcp))
>> +#define FSYM_TYPE(funcp) 0
>> +#endif /* !CONFIG_THUMB2_KERNEL */
>
> I'd really like to see these gone - otherwise they'll end up being used
> in code inappropriately.  I like things to be kept as simple as possible
> with as few opportunities for people to needlessly hook into internal
> implementation details.
>
> If you expose implementation details, people will use them, and then if
> you need to change the implementation, you've got a lot of code to deal
> with.

I guess I agree with that now ... with fncpy() implemented, there's
little legitimate use for the other macros, including the casting
macros.

I'll fold it all into fncpy() and see how that looks.

>
> I don't think we need to make this conditional on THUMB2 either - we're
> probably not wasting much by always clearing and copying the LSB.  And
> this isn't particularly performance code.
>

Agreed.  I originally tried to avoid impacting the ARM case, but that
adds complexity for little benefit.

Cheers
---Dave