On Tue, Jan 05, 2021 at 11:18:06AM +0100, Peter Zijlstra wrote: > On Tue, Jan 05, 2021 at 11:45:37AM +0800, Jiaxun Yang wrote: > > 在 2021/1/4 下午6:59, Peter Zijlstra 写道: > > > On Tue, Dec 29, 2020 at 08:55:59PM +0800, Tiezhu Yang wrote: > > > > +u64 perf_reg_abi(struct task_struct *tsk) > > > > +{ > > > > + if (test_tsk_thread_flag(tsk, TIF_32BIT_REGS)) > > > > + return PERF_SAMPLE_REGS_ABI_32; > > > > + else > > > > + return PERF_SAMPLE_REGS_ABI_64; > > > > +} > > > So we recently changed this on x86 to not rely on TIF flags. IIRC the > > > problem is that on x86 you can change the mode of a task without the > > > kernel being aware of it. Is something like that possible on MIPS as > > > well? > > > > Hi all, > > > > In MIPS world it's impossible to raise a thread to 64bit without kernel > > aware. > > Without STATUS.UX set it will trigger reserved instruction exception when > > trying > > to run 64bit instructions. > > The other way around is the case on x86, a 64bit program can create and > execute 32bit code sections without the kernel being aware. But if > clearing STATUS.UX has the same issue as setting it, that should not be > a problem for you. > > > However it may be possible to run with 32bit ABI without > > TIF_32BIT_REGS if user program didn't get ELF ABI right. I think > > that's out of our current consideration. > > Fair enough. > > > > The thing x86 does today is look at it's pt_regs state to determine the > > > actual state. > > It is possible to look at pt_regs Status.UX bit on MIPS. But it seems > > unnecessary > > as user can't change it. > > Ok, good. Then no objection, proceed! :-) this patch aims more to mips-next, while patch 2 and 3 are targeting tools/perf. Should I take them into mips-next, too ? Thomas. -- Crap can work. Given enough thrust pigs will fly, but it's not necessarily a good idea. [ RFC1925, 2.3 ]