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Re: Volunteer to work with Alpha port of lkcd

To: Matt Robinson <yakker@xxxxxxxxxxxxxxxxxxxx>
Subject: Re: Volunteer to work with Alpha port of lkcd
From: Brian Hall <brianw.hall@xxxxxxxxxx>
Date: Wed, 15 Dec 1999 08:38:08 -0700 (MST)
Cc: lkcd@xxxxxxxxxxx
In-reply-to: <Pine.SGI.3.94.991201103034.287753A-100000@xxxxxxxxxxxxxxxxxxxx>
Reply-to: Brian Hall <brianw.hall@xxxxxxxxxx>
Sender: owner-lkcd@xxxxxxxxxxx
OK, I am actively working on this now (the Linux Alpha machines I have access
to have had problems; I've put the kernel tree on an NFS mount so I can
continue to work).

Do I have to do the inline assembly to save the PC and RA registers, or can I
simply stuff them into the dump header structure? BTW, I notice lots of 32 bit
fields in the header, those will all have to be 64 bit for Alpha, won't they?
Certainly at least the registers will; I think having others in the structure
32 bit may cause alignment problems on the Alpha.

So, can I just make the dh_esp and dh_eip uint64_t, remove the inline asm and
the call to __dump_save_panic_regs, and just do:

/* This is __dump_execute */

dump_header.dh_esp = regs->pc;
/* from arch/alpha/kernel/traps.c, r26 appears to be ra */
dump_header.dh_eip = regs->r26;

/* dump out the header */

Also, what do you mean by putting a hook in die_if_kernel()? Do you mean to
call the kernel dump routine - dump_execute() ?

On 01-Dec-1999 Matt Robinson wrote:
> The first thing to do is to take the kernel code in
> arch/i386/kernel/vmdump.c and copy it to arch/alpha/kernel, modify
> the makefile, and then modify the calls for saving the pt_regs.
> The code for saving the registers is mostly correct, except for:
>         if (regs) {
>                 memcpy((void *)&(dump_header.dh_regs), (const void *)regs,
>                         sizeof(struct pt_regs));
>>               if (!user_mode(regs)) {
>>                       dump_header.dh_regs.esp = (unsigned long) (regs + 1);
>>               }
>         }
> Those lines aren't necessarily needed -- they are I386 specific.  We
> have to adjust the esp based on the processor mode.
> Also, the code for:
>         /* save the dump specific esp/eip */
>         __asm__ __volatile__("
>                 pushl %%eax\n
>                 movl  %%esp, %%eax\n
>                 movl  %%eax, %0\n
>                 popl  %%eax\n"
>                 : "=g" (dump_header.dh_esp)
>         );
>         __asm__ __volatile__("pushl  %eax\n");
>         __dump_save_panic_regs();
>         __asm__ __volatile__("popl   %eax\n");
> All of this is set up just to save the stack pointer and program
> counter for this box, as the pt_regs on I386 boxes don't necessarily
> point to the right location.  We want to be able to walk back from
> the exception where that is possible.
> In looking at the Alpha stuff, I think you can start by saving the PC
> and RA values (not sure which $XX they represent), and also put a hook
> into die_if_kernel() in traps.c.

Brian Hall <brianw.hall@xxxxxxxxxx>
Linux Consultant

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