On Sat, Mar 28, 2015 at 10:46 AM, Ingo Molnar <mi...@kernel.org> wrote: > * Denys Vlasenko <vda.li...@googlemail.com> wrote: >> This is a C function. [...] > > Arguably that's a self-inflicted wound of uclibc: nothing keeps it > from taking advantage of the syscall ABI and avoiding the double > save/restores.
It's not uclibc who calls write(), it's user program. IIRC uclibc can't make user program aware that write() is not clobbering registers. Even if it could do that via an __attribute__ somehow, it would be a violation of standards: write() is supposed to be an ordinary C function, users must be able to take its address and assign it to a pointer declared as ssize_t (*ptr)(int, const void *, size_t); Slapping __attribute__((different_abi)) onto write() makes that impossible, the signature no longer matches. Let me go back from hypothetics to the actual situation. We can't do such a drastic ABI change now, it's too big. But is looks like we can relax ABI wrt saving flags, because it's broken for some time, and no one complains. If we say that arith flags and DF are not saved, it may mean that we don't need to kill ourselves with awkward and costly (popf is 20 cycles) EFLAGS manipulations. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/