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

Akihiko Odaki posted 1 patch 10 months, 3 weeks ago
Patches applied successfully (tree, apply log)
git fetch https://github.com/patchew-project/qemu tags/patchew/20230611033434.14659-1-akihiko.odaki@daynix.com
Maintainers: Viktor Prutyanov <viktor.prutyanov@phystech.edu>
contrib/elf2dmp/main.c | 5 +++++
1 file changed, 5 insertions(+)
[PATCH] elf2dmp: Don't abandon when Prcb is set to 0
Posted by Akihiko Odaki 10 months, 3 weeks ago 
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
Re: [PATCH] elf2dmp: Don't abandon when Prcb is set to 0
Posted by Viktor Prutyanov 10 months, 3 weeks ago 
> 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?

NumberProcessors field is still set to qemu_elf.state_nr, how does WinDbg react to this?

Viktor
Re: [PATCH] elf2dmp: Don't abandon when Prcb is set to 0
Posted by Akihiko Odaki 10 months, 3 weeks ago 
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
Re: [PATCH] elf2dmp: Don't abandon when Prcb is set to 0
Posted by Viktor Prutyanov 10 months, 2 weeks ago 

> 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>
Re: [PATCH] elf2dmp: Don't abandon when Prcb is set to 0
Posted by Viktor Prutyanov 9 months ago 
>> 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?

Thank you,
Viktor Prutyanov
Re: [PATCH] elf2dmp: Don't abandon when Prcb is set to 0
Posted by Peter Maydell 9 months ago 
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

Patchew 2.1-devel-0870f84

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