Messages in this thread | | | Date | Wed, 26 Apr 2017 12:31:47 -0700 | From | Matthias Kaehlcke <> | Subject | Re: [PATCH] x86/mm/kaslr: Add operand size suffix to 'mul' instruction |
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Hi Kees,
El Wed, Apr 26, 2017 at 12:09:13PM -0700 Kees Cook ha dit:
> On Wed, Apr 26, 2017 at 12:01 PM, Matthias Kaehlcke <mka@chromium.org> wrote: > > In difference to gas clang doesn't seem to infer the size from the > > operands. Adding the suffix fixes the following error when building > > with clang: > > > > CC arch/x86/lib/kaslr.o > > /tmp/kaslr-dfe1ad.s: Assembler messages: > > /tmp/kaslr-dfe1ad.s:182: Error: no instruction mnemonic suffix given and > > no register operands; can't size instruction > > > > Signed-off-by: Matthias Kaehlcke <mka@chromium.org> > > --- > > arch/x86/lib/kaslr.c | 6 +++++- > > 1 file changed, 5 insertions(+), 1 deletion(-) > > > > diff --git a/arch/x86/lib/kaslr.c b/arch/x86/lib/kaslr.c > > index 121f59c6ee54..947d4aa92ff7 100644 > > --- a/arch/x86/lib/kaslr.c > > +++ b/arch/x86/lib/kaslr.c > > @@ -79,7 +79,11 @@ unsigned long kaslr_get_random_long(const char *purpose) > > } > > > > /* Circular multiply for better bit diffusion */ > > - asm("mul %3" > > +#ifdef CONFIG_X86_64 > > + asm("mulq %3" > > +#else > > + asm("mull %3" > > +#endif > > : "=a" (random), "=d" (raw) > > : "a" (random), "rm" (mix_const)); > > random += raw; > > > > Since there may be more of these and we try to avoid #ifdef in .c > files, I think we should create an isns helper macro and use it here > instead. Like: > > #ifdef CONFIG_X86_64 > # define ASM_MUL "mulq" > #else > # define ASM_MUL "mull" > #endif > > ... > > > asm(ASM_MUL " %3" ...
Sounds very reasonable. Thanks for the suggestion, I'll rework the patch.
Matthias
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