On Wed, Apr 26, 2017 at 12:01 PM, Matthias Kaehlcke <[email protected]> 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 <[email protected]> > --- > 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; > -- > 2.13.0.rc0.306.g87b477812d-goog >
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" ... -Kees -- Kees Cook Pixel Security
