Daniel Mierswa <impulze@xxxxxxxxxxx> writes: > On 08.01.2011 06:23, Ian Lance Taylor wrote: >> Good point, yes, you should add an explicit "memory" clobber. You don't >> need to explicitly clobber "cc". That is a fixed register (actually gcc >> calls it "flags") and as such gcc won't make any particular assumptions >> about it in any case. >> >> Ian > > Ok I'm curious as to why. > > If the information at > http://www.ibiblio.org/gferg/ldp/GCC-Inline-Assembly-HOWTO.html#ss5.3 is > of any use then I'd have to: > > [...] > If our instruction can alter the condition code register, we have to add > "cc" to the list of clobbered registers. > > If our instruction modifies memory in an unpredictable fashion, add > "memory" to the list of clobbered registers. > [...] > > I don't know if any of both situations may happen in my called function, > hence I'd have to supply both, or am I wrong? You can add a clobber of "cc" if you like, it just won't make any difference one way or another. On x86 gcc already assumes that the flags are clobbered by an asm. Ian
