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Re: Volunteer to work with Alpha port of lkcd

To: Brian Hall <brianw.hall@xxxxxxxxxx>
Subject: Re: Volunteer to work with Alpha port of lkcd
From: Matt Robinson <yakker@xxxxxxxxxxxxxxxxxxxx>
Date: Mon, 13 Dec 1999 13:08:17 -0800 (PST)
Cc: Matt Robinson <yakker@xxxxxxxxxxxxxxxxxxxx>, lkcd@xxxxxxxxxxx
In-reply-to: <XFMail.19991215083808.brianw.hall@xxxxxxxxxx>
Sender: owner-lkcd@xxxxxxxxxxx
On Wed, 15 Dec 1999, Brian Hall wrote:
|>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.

The problem is from panic(), you don't have the registers, so you
need to grab them.  That way the 'lcrash' code has a point to start
with as far as the failing process is concerned.  Hence the "if (regs)"

|>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 */

The dump_header uses pt_regs, and if the alpha stuff is translated
right for your build, it should be the right type without you having
to do anything.  Such as:

        regs->esp is 32-bit (long) for i386; however
        regs->pc is 64-bit (unsigned long) for alpha.

No type-casting should be necessary, assuming architecture compatible
pt_regs stuff is being used.

If you do see a problem, however, let me know and I'll fix it in the
main code.

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

Correct.  Be sure that panic() also calls 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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