On 01/28/2015 10:17 AM, Ard Biesheuvel wrote:
> On 28 January 2015 at 14:11, Alex Elder <el...@linaro.org> wrote:
>> On 01/28/2015 05:15 AM, Ard Biesheuvel wrote:
>>> On 28 January 2015 at 05:18, Behan Webster <beh...@converseincode.com>
>>> wrote:
>>>> From: Alex Elder <el...@linaro.org>
>>>>
>>>> My GCC-based build environment likes to call register r12 by the
>>>> name "ip" in inline asm. Behan Webster informed me that his Clang-
>>>> based build environment likes "r12" instead.
>>>>
>>>> Try to make them both happy.
>>>>
>>>> Signed-off-by: Alex Elder <el...@linaro.org>
>>>> Signed-off-by: Behan Webster <beh...@converseincode.com>
>>>> ---
>>>> arch/arm/mach-bcm/bcm_kona_smc.c | 9 +++++++--
>>>> 1 file changed, 7 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/arch/arm/mach-bcm/bcm_kona_smc.c
>>>> b/arch/arm/mach-bcm/bcm_kona_smc.c
>>>> index a55a7ec..3937bd5 100644
>>>> --- a/arch/arm/mach-bcm/bcm_kona_smc.c
>>>> +++ b/arch/arm/mach-bcm/bcm_kona_smc.c
>>>> @@ -106,9 +106,14 @@ int __init bcm_kona_smc_init(void)
>>>> * request result appropriately. This result value is found in r0
>>>> * when the "smc" request completes.
>>>> */
>>>> +#ifdef __clang__
>>>> +#define R12 "r12"
>>>> +#else /* !__clang__ */
>>>> +#define R12 "ip" /* gcc calls r12 "ip" */
>>>> +#endif /* !__clang__ */
>>>
>>> Why not just use r12 for both?
>>
>> Yes, that would have been an obvious fix. But the
>> assembler (in the GCC environment) doesn't accept that.
>>
>
> Mine has no problems with it at all
>
> $ echo 'mov r12, #0' | arm-linux-gnueabihf-gcc -c -x assembler-with-cpp -
>
> and grepping for r12 under arch/arm suggests the same
The use of "r12" is fine. But it's not just the assembler,
I believe it also involves gcc.
The problem is with the use of the __asmeq(x, y) macro.
If I assign the "ip" variable with "r12":
register u32 ip asm("r12"); /* Also called ip */
Then that's fine. However, this line then causes an error:
__asmeq("%0", "r12")
Apparently gcc uses register "ip" when it sees asm("r12"). So
attempting to verify the desired register got used with __asmeq()
causes a string mismatch--"ip" is not equal to "r12".
So I could use:
register u32 ip asm("r12"); /* Also called ip */
...
__asmeq("%0", "ip")
And that will build. But it's a little non-intuitive, and
I suspect that clang might (rightfully) have a failure in
this __asmeq() call.
-Alex
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