: 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

: 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

: 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 wrote: > On Sat, Sep 06, 2014 at 12:24:20AM +0100, behanw@converseincode.com wrote: >> From: Mark Charlebois >> >> 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