On Fri, Apr 25, 2008 at 5:01 PM, sahlot arvind <asahlot@xxxxxxxxx> wrote: > Guys, > > I am trying to understand the flow of control when an interrupt comes. > I am reading linux-2.6.24 src code and looking at > arch/arm/kernel/entry-armv.S. > At the bottom of this file I see the vector table as below - > > __vectors_start: > swi SYS_ERROR0 > b vector_und + stubs_offset > ldr pc, .LCvswi + stubs_offset > b vector_pabt + stubs_offset > b vector_dabt + stubs_offset > b vector_addrexcptn + stubs_offset > b vector_irq + stubs_offset > b vector_fiq + stubs_offset > > .globl __vectors_end > > > Here is not 'stubs_offset' a constant? and after seeing an IRQ where are we > branching by doing ' b vector_irq + stubs_offset' and what is the flow of > control??? > Thanks in advance. > stubs_offset is a constant decided by the assembler, note the .equ above. So actually, the vector_irq + stubs_offset (for example) = vector_irq + __vectors_start + 0x200 - __stubs_start = (vector_irq - __stubs_start) + 0x200 + __vectors_start And at run-time there will be dedicated page allocated for the vectors and the stubs code, and the stubs code will be copied at a offset of 0x200. see? 1st part is the vector_irq routine offset relative to the start of __stubs_start, __vectors_start is used to compensate for the assembler to generate relative branch instruction. > - A Sahlot > -- > http://linuxexplained.blogspot.com > ------------------------------------------------------------------- > List admin: http://lists.arm.linux.org.uk/mailman/listinfo/linux-arm-kernel > FAQ: http://www.arm.linux.org.uk/mailinglists/faq.php > Etiquette: http://www.arm.linux.org.uk/mailinglists/etiquette.php > -- Cheers - eric -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
