RE: 2.4.17: differences in arch/i386/kernel/entry.S ???

["Thomas Setzer" <info@thomas-setzer.de>]

> In short, does anyone know full sequence of steps that take place when
> an interrupt is raised either in kernel or in user mode?  Which
> functions get called, and, where are they stored in the source code?
> 

Hi Lukas,

that's what I found in the 2.4 Kernel Sources, Linux Kernel Internals,
Understanding the Linux Kernel about interrupt handling on ia32:


All interrupt handlers perform the same 4 basic actions:

1. Save the IRQ value and the registers contents in the 
Kernel Mode stack:

Code is stored in 'arch/i386/kernel/i8259.c':

27 /*
28  * Common place to define all x86 IRQ vectors
29  *
30  * This builds up the IRQ handler stubs using some ugly macros in
irq.h
31  *
32  * These macros create the low-level assembly IRQ routines that save
33  * register context and call do_IRQ(). do_IRQ() then does all the
34  * operations that are needed to keep the AT (or SMP IOAPIC)
35  * interrupt-controller happy.
36  */

Saving registers is the first task of the interrupt handler.
The interrupt handler for IRQn is named IRQn_interrupt, its
address is included in the interrupt gate stored in the
proper IDT entry.

The same BUILD_IRQ macro is duplicated 16 times, once for 
each IRQ number, so you'll get 16 different interrupt
handler entry points. Each BUILD_IRQ expands to the following
assembly language fragment:

IRQn_interrupt:
pushl $n-256
jmp common_interrupt

This saves on the stack the IRQ number associated with the interrupt
minus 256 (Subtracting 256 from an IRQ number yields a negative number. 
Positive numbers are reserved to identify system calls); the same code
for all interrupt handlers can then be executed while referring to this
number. The common code can be found in the BUILD_COMMON_IRQ macro,
which expands to the following assembly language fragment:

common_interrupt:
SAVE_ALL
call do_IRQ
jmp ret_from_intr

________________________________________________________________________
____
2. Send an acknowledgment to the PIC that is servicing the IRQ line,
thus allowing it to issue further interrupts.

Code is stored in ' arch/i386/kernel/irq.c':
That's not clear to me

________________________________________________________________________
3. Execute the interrupt service routines (ISRs) associated with all the
devices that share the IRQ.

Code is stored in ' arch/i386/kernel/irq.c': 

558 /*
559  * do_IRQ handles all normal device IRQ's (the special
560  * SMP cross-CPU interrupts have their own specific
561  * handlers).
562  */


________________________________________________________________________
__
4. Terminate by jumping to the ret_from_intr( ) address.

Code is stored in ' arch/i386/kernel/entry.S':
...
248 ENTRY(ret_from_intr)
249         GET_CURRENT(%ebx)
250 ret_from_exception:
251         movl EFLAGS(%esp),%eax          # mix EFLAGS and CS
252         movb CS(%esp),%al
253         testl $(VM_MASK | 3),%eax       
...


Hope this helps,

Regards,
Thomas

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