On Wed, May 17, 2023 at 9:25 PM Janneke Nieuwenhuizen <jann...@gnu.org> wrote: > Hi!
Hi, > Here are the > last 24 (WTF, 1980 wants their screensize back!?) lines (I don't know > how to get the full log from QEMU): > > --8<---------------cut here---------------start------------->8--- > --8<---------------cut here---------------end--------------->8--- > > Again, any help or insights higly appreciated! I've recently been doing this kind of debugging early boot-up process *a lot*, so maybe I could provide some tips indeed. For getting more lines of output, try console=com0 on gnumach cmdline, and run qemu with -nographic -serial stdio or something like that. Other than that, just attach gdb and see what it crashes on? Like this: $ gdb /path/to/gnumach (gdb) tar rem :1234 (gdb) b i386_exception (gdb) b task_terminate (gdb) b Panic (gdb) add-symbol-file /path/to/rumpdisk.static blah-blah (y/n?) y (gdb) c This is *so much* easier to do with statically linked non-PIE binaries loaded by gnumach/GRUB at startup compared to hunting for shared library .text addresses and single-stepping through code pages getting paged in upon first access (can't place a breakpoint before the page gets paged in!), so enjoy it while it lasts :) If you do hit i386_exception, you can look at active_threads[0]->task->name to understand what task it is (though it's likely to be just the rumpdisk in your case). If you step up several frames (perhaps just one), you'll find a 'regs' argument being passed to a function; from there you can extract the faulting %eip, and then can disas around it to see what it is (again, much easier with symbols!). The trick I like to use is I, upon hitting an exception, re-set all the registers to the values described by 'regs', just like this: (gdb) set $rsp = $2.uesp (gdb) set $rip = $2.eip ...and so on (don't forget to switch back to the topmost frame first, with 'down' or 'select-frame') and that basically rewinds time to when the fault has happened, and from there you can see the userland backtrace and inspect the full state at the time of the fault. Sergey
