On Thu, 2005-08-11 at 11:28 -0400, linux-os (Dick Johnson) wrote: > On Thu, 11 Aug 2005, Coywolf Qi Hunt wrote: > > > On 8/11/05, Steven Rostedt <[EMAIL PROTECTED]> wrote: > >> On Thu, 2005-08-11 at 10:04 -0400, linux-os (Dick Johnson) wrote: > >>> Every interrupt software, or hardware, results in the branched > >>> procedure being executed with the interrupts OFF. That's why > >>> one of the first instructions in the kernel entry for a syscall > >>> is 'sti' to turn them back on. Look at entry.S, line 182. This > >>> occurs any time a trap occurs as well (Page 26-168, i486 > >>> Programmer's reference manual). FYI, this is helpful when > >>> designing/debugging complex interrupt-service routines since > >>> you can execute the interrupt with a software 'INT' instruction > >>> (with the correct offset from the IRQ you are using). The software > >>> doesn't 'know' where the interrupt came from, HW or SW. > >> > >> I'm looking at 2.6.13-rc6-git1 line 182 of entry.S and I don't see it. > >> Must be a different kernel. > >> > >> According to the documentation that I was looking at, a trap in x86 does > >> _not_ turn off interrupts. > >> > > ... > >> > >> I don't see a sti here. > > > > Search for sysenter_entry. This is where the stack is switched > to the kernel stack. Then the code falls through past the > next label, sysenter_past_esp. The very next instruction > after the kernel stack has been set is 'sti'. Clear as day.
I just applied the following to one of my kernels: -- arch/i386/kernel/entry.S (revision 274) +++ arch/i386/kernel/entry.S (working copy) @@ -184,6 +184,7 @@ ENTRY(sysenter_entry) movl TSS_sysenter_esp0(%esp),%esp sysenter_past_esp: + ud2 sti pushl $(__USER_DS) pushl %ebp And booted it. The system is up and running, so I really don't think that the sysenter_entry is used for system calls. Not so "Clear as day"! -- Steve - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/