On 2012-01-22 15:20, Francis Moreau wrote: > Hello, > > I'm trying to debug a 64 bits kernel (3.2) using qemu (with and > without KVM support). The host is also 64 bits. Version of gdb I'm > using is 7.1. > > To do that I simply start qemu like the following: > > $ qemu-system-x86_64 -kernel bzImage -append "root=/dev/sda1 > console=ttyS0 3" -serial stdio -S -s > > and in another term, I start gdb like this: > > $ gdb vmlinux > $ target remote locahost:1234 > $ b prepare_namespace > $ continue > Continuing. > Remote 'g' packet reply is too long: af75919effffffff0............. > > So it fails when gdb stops on the breakpoint with the above message. > > If I try to dump the backtrace I got: > > $ bt > Target is executing. > $ info thread > * 1 Thread 1 (CPU#0 [running]) (running) > > But the VM seems to be stopped because if I'm asking the status to qemu: > > $ info status > VM status: paused > > I also tried qemu with KVM support but I get one more problem: gdb is > ignoring my breakpoint. > > Could anybody help me to make gdb work ?
When stopping the guest with -S before it booted, gdb will interrupt it while it is still in 16-bit real mode. Later on, when Linux runs, the guest is in 64-bit protected mode. gdb is not prepared for such a switch. All you can do: - let the guest run until it surely reached 64-bit mode - interrupt it and set a breakpoint at the desired early-boot location, important: if using KVM, set a hardware breakpoint! - continue and reboot the guest without detaching gdb - on next boot, the breakpoint will trigger HTH, Jan
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