[Crash-utility] Fix pvops Xen detection for kernels >= v4.20

[David Mair]

Hi Petr,

Thank you, while I didn't get to the point of failure I'm please to see 
I was not wrong in finding what I thought was evidence the coredump is 
not in a format crash is able to read...cause not being the generation 
of the coredump but, instead, the rather classic example of a kernel 
change that made crash obsolete in the same product.

I expect to be working on all needed crash changes from now.

-- 
David.

On 6/25/21 9:21 AM, Petr Tesařík wrote:
> Kernel commit 5c83511bdb9832c86be20fb86b783356e2f58062 removed 
> pv_init_ops, and later commit 054ac8ad5ebe4a69e1f0e842483821ddbe560121 
> removed the Xen-specific paravirt patch function. As a result, pvops Xen 
> dumps are no longer recognized as Xen dumps, and virtual-to-physical 
> translation fails.
> 
> Use the value of xen_start_info to determine whether the kernel is 
> running in Xen PV mode. This pointer is set during the initialization of 
> a PV domain. Kudos to Juergen Gross, who suggested this check.
> 
> Signed-off-by: Petr Tesarik <ptesarik at suse.com>
> ---
>   kernel.c |   34 ++++++++++++++++++++++++++++------
>   1 file changed, 28 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel.c b/kernel.c
> index e123f76..36fdea2 100644
> --- a/kernel.c
> +++ b/kernel.c
> @@ -95,6 +95,7 @@ static ulong __dump_audit(char *);
>   static void dump_audit(void);
>   static char *vmcoreinfo_read_string(const char *);
>   static void check_vmcoreinfo(void);
> +static int is_pvops_xen(void);
> 
> 
>   /*
> @@ -109,7 +110,6 @@ kernel_init()
>       char *rqstruct;
>       char *rq_timestamp_name = NULL;
>       char *irq_desc_type_name;
> -    ulong pv_init_ops;
>       struct gnu_request req;
> 
>       if (pc->flags & KERNEL_DEBUG_QUERY)
> @@ -169,11 +169,7 @@ kernel_init()
>                              error(FATAL, "cannot malloc m2p page.");
>       }
> 
> -    if (PVOPS() && symbol_exists("pv_init_ops") &&
> -        readmem(symbol_value("pv_init_ops"), KVADDR, &pv_init_ops,
> -        sizeof(void *), "pv_init_ops", RETURN_ON_ERROR) &&
> -        ((p1 = value_symbol(pv_init_ops)) &&
> -        (STREQ(p1, "xen_patch") || STREQ(p1, 
> "paravirt_patch_default")))) {
> +    if (is_pvops_xen()) {
>           kt->flags |= ARCH_XEN | ARCH_PVOPS_XEN;
>           kt->xen_flags |= WRITABLE_PAGE_TABLES;
>           if (machine_type("X86"))
> @@ -10709,6 +10705,32 @@ paravirt_init(void)
>       }
>   }
> 
> +static int
> +is_pvops_xen(void)
> +{
> +    ulong addr;
> +    char *sym;
> +
> +    if (!PVOPS())
> +        return FALSE;
> +
> +    if (symbol_exists("pv_init_ops") &&
> +        readmem(symbol_value("pv_init_ops"), KVADDR, &addr,
> +        sizeof(void *), "pv_init_ops", RETURN_ON_ERROR) &&
> +        (sym = value_symbol(addr)) &&
> +        (STREQ(sym, "xen_patch") ||
> +         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;
> +
> +    return FALSE;
> +}
> +
>   /*
>    *  Get the kernel's xtime timespec from its relevant location.
>    */
>