On Mon, 15 Oct 2018, Russell King - ARM Linux wrote: > On Mon, Oct 15, 2018 at 06:35:33PM -0400, Nicolas Pitre wrote: > > On Tue, 16 Oct 2018, Stefan Agner wrote: > > > > > GCC documentation says naked functions should only use basic ASM > > > syntax. The extended ASM or mixture of basic ASM and "C" code is > > > not guaranteed. Currently it seems to work though. > > > > > > Furthermore with Clang using parameters in extended asm in a > > > naked function is not supported: > > > arch/arm/mm/copypage-v4wb.c:47:9: error: parameter references not > > > allowed in naked functions > > > : "r" (kto), "r" (kfrom), "I" (PAGE_SIZE / 64)); > > > ^ > > > > > > Use a regular function to be more portable. Also use volatile asm > > > to avoid unsolicited optimizations. > > > > > > Tested with qemu versatileab machine and versatile_defconfig and > > > qemu mainstone machine using pxa_defconfig compiled with GCC 7.2.1 > > > and Clang 7.0. > > > > > > Link: https://github.com/ClangBuiltLinux/linux/issues/90 > > > Reported-by: Joel Stanley <[email protected]> > > > Signed-off-by: Stefan Agner <[email protected]> > > > --- > > > arch/arm/mm/copypage-fa.c | 17 +++++++++++------ > > > arch/arm/mm/copypage-feroceon.c | 17 +++++++++++------ > > > arch/arm/mm/copypage-v4mc.c | 14 +++++++++----- > > > arch/arm/mm/copypage-v4wb.c | 17 +++++++++++------ > > > arch/arm/mm/copypage-v4wt.c | 17 +++++++++++------ > > > arch/arm/mm/copypage-xsc3.c | 17 +++++++++++------ > > > arch/arm/mm/copypage-xscale.c | 13 ++++++++----- > > > 7 files changed, 72 insertions(+), 40 deletions(-) > > > > > > diff --git a/arch/arm/mm/copypage-fa.c b/arch/arm/mm/copypage-fa.c > > > index ec6501308c60..33ccd396bf99 100644 > > > --- a/arch/arm/mm/copypage-fa.c > > > +++ b/arch/arm/mm/copypage-fa.c > > > @@ -17,11 +17,16 @@ > > > /* > > > * Faraday optimised copy_user_page > > > */ > > > -static void __naked > > > -fa_copy_user_page(void *kto, const void *kfrom) > > > +static void fa_copy_user_page(void *kto, const void *kfrom) > > > { > > > - asm("\ > > > - stmfd sp!, {r4, lr} @ 2\n\ > > > + register void *r0 asm("r0") = kto; > > > + register const void *r1 asm("r1") = kfrom; > > > + > > > + asm( > > > + __asmeq("%0", "r0") > > > + __asmeq("%1", "r1") > > > + "\ > > > + stmfd sp!, {r4} @ 2\n\ > > > mov r2, %2 @ 1\n\ > > > 1: ldmia r1!, {r3, r4, ip, lr} @ 4\n\ > > > stmia r0, {r3, r4, ip, lr} @ 4\n\ > > > @@ -34,9 +39,9 @@ fa_copy_user_page(void *kto, const void *kfrom) > > > subs r2, r2, #1 @ 1\n\ > > > bne 1b @ 1\n\ > > > mcr p15, 0, r2, c7, c10, 4 @ 1 drain WB\n\ > > > - ldmfd sp!, {r4, pc} @ 3" > > > + ldmfd sp!, {r4} @ 3" > > > : > > > - : "r" (kto), "r" (kfrom), "I" (PAGE_SIZE / 32)); > > > + : "r" (r0), "r" (r1), "I" (PAGE_SIZE / 32)); > > > > This is still wrong as you list r0 and r1 in the input operand list > > where they must remain constant but the code does modify them. You > > should list them in the output operand list with the "&" attribute. Also > > r2 should be listed in the clobbered list. > > Either we keep these as naked functions (and, if Clang wants to > try to inline naked functions which makes no sense, also mark them > as noinline) or we make them proper functions and also add (eg) r4 > to the clobber list and get rid of the stacking of that register > along with LR/PC.
Yes, indeed. I'd say: remove the naked stuff, and let the compiler do the prologue/epilogue itself (or inline it for that matter). And don't force pointers and counter into particular registers. This way r0-r3 could be used as temporaries since they're probably already clobbered by the call to kmap_atomic() anyway. That is likely to be better than forcing ip/lr as temporaryes. Nicolas
