Re: Macintosh Quadra 950 Not Booting

[Greg Andrzejewski <gregta@gmail.com>]

On Sun, Aug 9, 2015 at 8:32 PM, Finn Thain <fthain@telegraphics.com.au> wrote:

On Sun, 9 Aug 2015, Geert Uytterhoeven wrote:
> It's the internal buffer for printk():
>
> kernel/printk/printk.c:static char __log_buf[__LOG_BUF_LEN] ...

Right, thanks. If I run this,

$ m68k-linux-gnu-readelf -a boot/vmlinux-4.1.4-mac | grep __log_buf
  1723: 003286c8 16384 OBJECT  LOCAL  DEFAULT   10 __log_buf

I can see that it has address 0x003286c8 and length 16384 bytes. I believe
this is the physical address. But I have no idea whether it will show up
in MacsBug at that address.

Don't ask me to explain why, but it does. I think those are virtual addresses, but by good fortune it just so happens to directly translate to a physical address. You can do a quick sanity check by inspecting the value of log_buf, which is a pointer to __log_buf, so should contain the value 003286c8.

If it could be located easily and if it did not get clobbered (entirely or
partially) by the ROM or by MacOS, it could be very useful at times.

I've had good luck with it remaining intact as long as you drop into MacsBug right away. Only downside is earlyprintk != printk, as I've come to find out, so those oh so valuable early messages won't be present.

-Greg