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Debugging a 64-bit kernel in qemu
- From: Markus Duft <markus dot duft at salomon dot at>
- To: qemu-devel at nongnu dot org, gdb at sourceware dot org
- Date: Mon, 03 Jan 2011 11:27:00 +0100
- Subject: Debugging a 64-bit kernel in qemu
I have been playing a little with this: I'm writing a kernel for both x86 and x86-64. While doing so, i'd like to debug the kernel using qemu (and it's gdb stub) and gdb. This worked very well until qemu-0.11.1 (gdb version does not seem to play any role...). From there on, debugging the 64 bit version no longer works. My sessions look like this with qemu-0.13.50 (and any version above 0.11.1, actually...):
mduft@s01en22 /big/Privat/osdev/tachyon2 $ x86_64-pc-linux-gnu-gdb .build/x86_64/x86_64-tachyon
GNU gdb (GDB) 126.96.36.19910103-cvs
Reading symbols from /big/Privat/osdev/tachyon2/.build/x86_64/x86_64-tachyon...done.
(gdb) target remote:1234
Remote debugging using :1234
0x0000000000000000 in ?? ()
(gdb) b boot
Breakpoint 1 at 0xffffffff80119000: file /big/Privat/osdev/tachyon2/core/tachyon.boot/Entry.cc, line 25.
Remote 'g' packet reply is too long: 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
actuallly, i _can_ debug the kernel, nut only until the long mode switch occurs. after this point: no luck... :[
now for the questions:
1) is this a problem with qemu or was qemu "fixed" and gdb has a problem?
(that's why i CCd the gdb list ;)).
2) is there any plan to fix this issue?
3) is there some kind of workaround i can use (i'd be happy with an ugly/unsupported patch too, since i build all my stuff myself ;)).
Thanks in advance!