[Crash-utility] [PATCH] Fix pvops Xen detection for arm machine

[HAGIO KAZUHITO(萩尾 一仁)]

Hi Qi, Xen folks,

-----Original Message-----
> Since the xen_start_info on the arm/arm64 platform is static defined:
> 
> ./arm/xen/enlighten.c:40:static struct start_info _xen_start_info;
> ./arm/xen/enlighten.c:41:struct start_info *xen_start_info = &_xen_start_info;
> ./arm/xen/enlighten.c:42:EXPORT_SYMBOL(xen_start_info);
> 
> The is_pvops_xen() in commit 4badc6229c69f5cd9da7eb7bdf400a53ec6db01a
> ("Fix pvops Xen detection for kernels >= v4.20") always return TRUE.
> Then the following error will be reported because p2m_mid_missing
> and xen_p2m_addr are not defined:
> 
> 	crash: cannot resolve "p2m_top"
> 
> Fix it by using xen_vcpu_id instead of xen_start_info to detect Xen dumps.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch at bytedance.com>
> ---
>  kernel.c | 21 ++++++++++++++++-----
>  1 file changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel.c b/kernel.c
> index f4598ea..b216fbe 100644
> --- a/kernel.c
> +++ b/kernel.c
> @@ -10745,6 +10745,9 @@ is_pvops_xen(void)
>  {
>  	ulong addr;
>  	char *sym;
> +	struct syment * sp;
> +	ulong ptr;
> +	int i;
> 
>  	if (!PVOPS())
>  		return FALSE;
> @@ -10757,11 +10760,19 @@ is_pvops_xen(void)
>  	     STREQ(sym, "paravirt_patch_default")))
>  		return TRUE;
> 
> -	if (symbol_exists("xen_start_info") &&
> -	    readmem(symbol_value("xen_start_info"), KVADDR, &addr,
> -	    sizeof(void *), "xen_start_info", RETURN_ON_ERROR) &&
> -	    addr != 0)
> -		return TRUE;
> +	sp = per_cpu_symbol_search("xen_vcpu_id");
> +	if (sp) {
> +		for (i = 0; i < NR_CPUS; i++) {
> +			if (!kt->__per_cpu_offset[i])
> +				continue;

Thanks for the patch.

But seems that kt->__per_cpu_offset is initialized after the is_pvops_xen()
call.  So this block always return FALSE?

Is there any other variable that we can use?  or another solution..

Thanks,
Kazu

> +
> +			ptr = sp->value + kt->__per_cpu_offset[i];
> +			if (ptr && readmem(ptr, KVADDR, &ptr, sizeof(uint32_t),
> +			    "xen_vcpu_id", FAULT_ON_ERROR))
> +				return TRUE;
> +			return FALSE;
> +		}
> +	}
> 
>  	return FALSE;
>  }
> --
> 2.11.0