Re: [Qemu-devel] [[RFC][Bugfix:isapc lapic state]] Bugfix: isapc:apic_state ?Start QEMU with "qemu-system-x86_64 -nographic -M isapc -serial none -monitor stdio" ?and enter "info lapic" at the monitor prompt ⇒ Segmentation fault

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Mon, Mar 27, 2017 at 03:49:13PM +0530, Tejaswini wrote:

Thanks for the patch!

Please CC the maintainers of target/i386/helper.c:

  $ scripts/get_maintainer.pl -f target/i386/helper.c
  Paolo Bonzini <pbonzini@redhat.com> (maintainer:X86)
  Richard Henderson <rth@twiddle.net> (maintainer:X86)
  Eduardo Habkost <ehabkost@redhat.com> (maintainer:X86)

Please shorten the subject line:

  [[RFC][Bugfix:isapc lapic state]] Bugfix: isapc:apic_state ?Start QEMU with "qemu-system-x86_64 -nographic -M isapc -serial none -monitor stdio" ?and enter "info lapic" at the monitor prompt ⇒ Segmentation fault

I suggest:

  [PATCH] target-i386: fix "info lapic" segfault on isapc

The commit message (subject line) should be a short summary of the
patch.  Typically this is below 80 or even 72 characters.  Details go in
the commit description (email body before '---'), which can be
arbitrarily long.  Please move the command-line for reproducing the
segmentation fault into the commit description.

Please don't add extra tags to the Subject line unless you're sure they
are commonly used in QEMU (e.g. "[Bugfix:isapc lapic state]] Bugfix:
isapc:apic_state").

> From: Tejaswini Poluri <tejaswinipoluri3@gmail.com>
> 
> 	The error occurs for only isapc machine type as it doesn't have apic state
> 	The cpu->apic_state of isapc is NULL. Hence added null pointer check in
> 	x86_cpu_dump_local_apic_state()

Please remove the indentation.

> 
> Signed-off-by: Tejaswini Poluri <tejaswinipoluri3@gmail.com>
> ---
>  target/i386/helper.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/target/i386/helper.c b/target/i386/helper.c
> index e2af340..1a8e3dd 100644
> --- a/target/i386/helper.c
> +++ b/target/i386/helper.c
> @@ -327,7 +327,10 @@ void x86_cpu_dump_local_apic_state(CPUState *cs, FILE *f,
>      X86CPU *cpu = X86_CPU(cs);
>      APICCommonState *s = APIC_COMMON(cpu->apic_state);
>      uint32_t *lvt = s->lvt;
> -
> +    if (!s) {
> +        cpu_fprintf(f, "apic state not available\n");
> +        return;
> +    }

Did you test this code?

The dereference one line above will still cause a segfault:

  uint32_t *lvt = s->lvt;  <--- s is NULL!

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