On 2011-08-26 19:34, Blue Swirl wrote: > 2011/8/26 Jan Kiszka <jan.kis...@siemens.com>: >> On 2011-08-26 16:21, Zeus Gómez Marmolejo wrote: >>> Hi all, >>> >>> I just want to do a very simple task. I'm using QEMU for debugging a new OS >>> and I see that there is a memory region that is being updated by an unknown >>> task. I don't know if it's another process or the kernel itself. >>> >>> So I would like to put a physical memory watchpoint. I don't know how to do >>> that. As the GDB stub is operating using virtual addressing, I cannot place >>> a watchpoint on an address as it's not stopping. >>> >>> To make it short, I want the equivalent of the Bochs command "watch write >>> addr", which inserts a write watch point at physical address 'addr'. I >>> haven't seen this is possible on the QEMU monitor... >> >> Indeed, it isn't. It's impossible with KVM (due to lacking hardware >> support) but would be feasible with TCG if you extend (or ad-hoc hack) >> QEMU code accordingly. > > Why impossible? The existing watchpoints replace original physical > memory with io_mem_watch MMIO, virtual addresses are translated to > physical in exec.c:tlb_set_page(). The only missing piece is to allow > setting watchpoints with physical addresses directly. > > Since KVM can handle MMIO, I think it should also be able to handle > watchpoints.
KVM uses x86 debug registers for watchpoints. And the SDM states: 16.2.1 Debug Address Registers (DR0-DR3) Each of the debug-address registers (DR0 through DR3) holds the 32-bit linear address of a breakpoint (see Figure 16-1). Breakpoint comparisons are made before physical address translation occurs. [...] Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux
