When I compile
int main()
{
u64 foo, tmp;
// This works for both clang and gcc
asm volatile(
" mrs %0, mair_el1\n"
" bfi %0, %1, %2, #8\n"
" msr mair_el1, %0\n"
" isb\n"
: "=&r" (tmp)
: "r" (foo), "i" (MT_NORMAL * 8));
}
with clang I get:
00000000004004f0 <main>:
4004f0: d538a208 mrs x8, mair_el1
4004f4: b3601d08 bfi x8, x8, #32, #8
4004f8: d518a208 msr mair_el1, x8
4004fc: d5033fdf isb
400500: 2a1f03e0 mov w0, wzr
400504: d65f03c0 ret
When I compile it with GCC I get:
0000000000400510 <main>:
400510: d10043ff sub sp, sp, #0x10
400514: f94003e1 ldr x1, [sp]
400518: d538a200 mrs x0, mair_el1
40051c: b3601c20 bfi x0, x1, #32, #8
400520: d518a200 msr mair_el1, x0
400524: d5033fdf isb
400528: f90007e0 str x0, [sp,#8]
40052c: 910043ff add sp, sp, #0x10
400530: d65f03c0 ret
When I compile
int main()
{
u64 foo, tmp;
// This fails for clang but not gcc
asm volatile(
" mrs %0, mair_el1\n"
" bfi %0, %1, #%2, #8\n"
" msr mair_el1, %0\n"
" isb\n"
: "=&r" (tmp)
: "r" (foo), "i" (MT_NORMAL * 8));
}
Clang fails and GCC generates:
00000000004004f0 <main>:
4004f0: d538a208 mrs x8, mair_el1
4004f4: b3601d08 bfi x8, x8, #32, #8
4004f8: d518a208 msr mair_el1, x8
4004fc: d5033fdf isb
400500: 2a1f03e0 mov w0, wzr
400504: d65f03c0 ret
On Mon, Sep 8, 2014 at 3:53 AM, Will Deacon <will.dea...@arm.com> wrote:
> On Sat, Sep 06, 2014 at 12:24:20AM +0100, beh...@converseincode.com wrote:
>> From: Mark Charlebois <charl...@gmail.com>
>>
>> Fix variable types for 64-bit inline assembly.
>>
>> This patch now works with both gcc and clang.
>
> Really? This looks like something the clang needs to do better on, as I
> really don't see people adding these casts to future code. They're ugly and
> redundant (or GCC).
>
> This hunk:
>
>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>> index c555672..6894ef3 100644
>> --- a/arch/arm64/mm/mmu.c
>> +++ b/arch/arm64/mm/mmu.c
>> @@ -94,7 +94,7 @@ static int __init early_cachepolicy(char *p)
>> */
>> asm volatile(
>> " mrs %0, mair_el1\n"
>> - " bfi %0, %1, #%2, #8\n"
>> + " bfi %0, %1, %2, #8\n"
>> " msr mair_el1, %0\n"
>> " isb\n"
>> : "=&r" (tmp)
>
> also looks fishy. Does gas accept that without the '#' prefix?
>
> Will
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