* Denys Vlasenko <vda.li...@googlemail.com> wrote: > On Mon, Mar 9, 2015 at 12:46 PM, Ingo Molnar <mi...@kernel.org> wrote: > > > > * Andy Lutomirski <l...@amacapital.net> wrote: > > > >> >> */ > >> >> unsigned long stack[64]; > >> >> > >> >> Last I checked, 0x100 != 64. Also, wow, this is kind of disgusting. :) > >> > > >> > > >> > Seems to be unused: I commented it out on "defconfig" build > >> > and got no build errors. > >> > >> It's used. On 32-bit, NMIs don't use task gates (I don't know why), > > > > So task gates were a sexy hardware acceleration feature, eons ago, and > > we used to rely on them a lot, > > IIRC task gates weren't used in Linux at first, [...]
AFAIK task gates were used to demo i386 context switching between tasks, a certain famous ABABABAB... pair of tasks printing to the console :-) So task gates were used for context switching in Linux before it was called Linux! :-) Check out the first released version: https://www.kernel.org/pub/linux/kernel/Historic/linux-0.01.tar.gz It already does: /* * switch_to(n) should switch tasks to task nr n, first * checking that n isn't the current task, in which case it does nothing. * This also clears the TS-flag if the task we switched to has used * tha math co-processor latest. */ #define switch_to(n) {\ struct {long a,b;} __tmp; \ __asm__("cmpl %%ecx,_current\n\t" \ "je 1f\n\t" \ "xchgl %%ecx,_current\n\t" \ "movw %%dx,%1\n\t" \ "ljmp %0\n\t" \ "cmpl %%ecx,%2\n\t" \ "jne 1f\n\t" \ "clts\n" \ "1:" \ ::"m" (*&__tmp.a),"m" (*&__tmp.b), \ "m" (last_task_used_math),"d" _TSS(n),"c" ((long) task[n])); \ } That LJMP is the TSS switch. And in kernel/sched.c we did: void sched_init(void) { int i; struct desc_struct * p; set_tss_desc(gdt+FIRST_TSS_ENTRY,&(init_task.task.tss)); :-) Thanks, Ingo -- 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/
