Re: [PATCH] elf2dmp: Don't abandon when Prcb is set to 0

[Peter Maydell]

On Sun, 30 Jul 2023 at 20:52, Viktor Prutyanov
<viktor.prutyanov@phystech.edu> wrote:
>
>
> >> On 2023/06/12 12:42, Viktor Prutyanov wrote:
> >>
> >>>> Prcb may be set to 0 for some CPUs if the dump was taken before they
> >>>> start. The dump may still contain valuable information for started CPUs
> >>>> so don't abandon conversion in such a case.
> >>>>
> >>>> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> >>>> ---
> >>>> contrib/elf2dmp/main.c | 5 +++++
> >>>> 1 file changed, 5 insertions(+)
> >>>>
> >>>> diff --git a/contrib/elf2dmp/main.c b/contrib/elf2dmp/main.c
> >>>> index d77b8f98f7..91c58e4424 100644
> >>>> --- a/contrib/elf2dmp/main.c
> >>>> +++ b/contrib/elf2dmp/main.c
> >>>> @@ -312,6 +312,11 @@ static int fill_context(KDDEBUGGER_DATA64 *kdbg,
> >>>> return 1;
> >>>> }
> >>>>
> >>>> + if (!Prcb) {
> >>>> + eprintf("Context for CPU #%d is missing\n", i);
> >>>> + continue;
> >>>> + }
> >>>> +
> >>>> if (va_space_rw(vs, Prcb + kdbg->OffsetPrcbContext,
> >>>> &Context, sizeof(Context), 0)) {
> >>>> eprintf("Failed to read CPU #%d ContextFrame location\n", i);
> >>>>
> >>>> --
> >>>> 2.40.1
> >>>
> >>> Hi Akihiko,
> >>>
> >>> How this fix can be tested?
> >>
> >> It is a bit difficult to test it as you need to interrupt the very early
> >> stage of boot. I applied the following change to TCG so that it stops
> >> immediately after the first processor configures Prcb.
> >>
> >> diff --git a/target/i386/tcg/sysemu/misc_helper.c
> >> b/target/i386/tcg/sysemu/misc_helper.c
> >> index e1528b7f80..f68eba9cac 100644
> >> --- a/target/i386/tcg/sysemu/misc_helper.c
> >> +++ b/target/i386/tcg/sysemu/misc_helper.c
> >> @@ -25,6 +25,9 @@
> >> #include "exec/address-spaces.h"
> >> #include "exec/exec-all.h"
> >> #include "tcg/helper-tcg.h"
> >> +#include "exec/gdbstub.h"
> >> +#include "hw/core/cpu.h"
> >> +#include "sysemu/runstate.h"
> >>
> >> void helper_outb(CPUX86State *env, uint32_t port, uint32_t data)
> >> {
> >> @@ -217,7 +220,10 @@ void helper_wrmsr(CPUX86State *env)
> >> env->segs[R_FS].base = val;
> >> break;
> >> case MSR_GSBASE:
> >> + printf("%s: %" PRIx64 "\n", __func__, val);
> >> env->segs[R_GS].base = val;
> >> + gdb_set_stop_cpu(current_cpu);
> >> + vm_stop(RUN_STATE_PAUSED);
> >> break;
> >> case MSR_KERNELGSBASE:
> >> env->kernelgsbase = val;
> >>
> >>> NumberProcessors field is still set to qemu_elf.state_nr, how does WinDbg 
> >>> react to this?
> >>
> >> If Prcb for processor 1 is missing, WinDbg outputs: KiProcessorBlock[1]
> >> is null.
> >> You can still debug the started processors with no issue.
> >>
> >> Regards,
> >> Akihiko Odaki
> >>
> >>> Viktor
> >
> > Reviewed-by: Viktor Prutyanov <viktor.prutyanov@phystech.edu>
>
> Hi Peter,
>
> Could you please put Akihiko's patch into your branch?

Sure. I've applied this to target-arm.next and should
be doing a pullreq for it later today or tomorrow.

-- PMM