Re: [PATCH] libs/guest: Move the guest ABI check earlier into xc_dom_parse_image()

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 17/08/2021 16:19, Jane Malalane wrote:
> Xen may not support 32-bit PV guest for a number of reasons (lack of
> CONFIG_PV32, explicit pv=no-32 command line argument, or implicitly
> due to CET being enabled) and advertises this to the toolstack via the
> absence of xen-3.0-x86_32p ABI.
>
> Currently, when trying to boot a 32-bit PV guest, the ABI check is too
> late and the build explodes in the following manner yielding an
> unhelpful error message:
>
>   xc: error: panic: xg_dom_boot.c:121: xc_dom_boot_mem_init: can't allocate low memory for domain: Out of memory
>   libxl: error: libxl_dom.c:586:libxl__build_dom: xc_dom_boot_mem_init failed: Operation not supported
>   libxl: error: libxl_create.c:1573:domcreate_rebuild_done: Domain 1:cannot (re-)build domain: -3
>   libxl: error: libxl_domain.c:1182:libxl__destroy_domid: Domain 1:Non-existant domain
>   libxl: error: libxl_domain.c:1136:domain_destroy_callback: Domain 1:Unable to destroy guest
>   libxl: error: libxl_domain.c:1063:domain_destroy_cb: Domain 1:Destruction of domain failed
>
> Move the ABI check earlier into xc_dom_parse_image() along with other
> ELF-note feature checks.  With this adjustment, it now looks like
> this:
>
>   xc: error: panic: xg_dom_boot.c:88: xc_dom_compat_check: guest type xen-3.0-x86_32p not supported by xen kernel, sorry: Invalid kernel
>   libxl: error: libxl_dom.c:571:libxl__build_dom: xc_dom_parse_image failed
>   domainbuilder: detail: xc_dom_release: called
>   libxl: error: libxl_create.c:1573:domcreate_rebuild_done: Domain 11:cannot (re-)build domain: -3
>   libxl: error: libxl_domain.c:1182:libxl__destroy_domid: Domain 11:Non-existant domain
>   libxl: error: libxl_domain.c:1136:domain_destroy_callback: Domain 11:Unable to destroy guest
>   libxl: error: libxl_domain.c:1063:domain_destroy_cb: Domain 11:Destruction of domain failed
>
> Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
> Signed-off-by: Jane Malalane <jane.malalane@citrix.com>

FWIW, Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

The net behaviour of `xl create` is still not great (the -3 in
particular is ESRCH looking for qemu which isn't remotely relevant), but
at least with this change, you get "guest type xen-3.0-x86_32p not
supported by xen" out of libxc which is the root cause of the failure.

~Andrew