From: "Roger Pau Monné" <roger.pau@citrix.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
Julien Grall <julien@xen.org>, Wei Liu <wl@xen.org>,
Paul Durrant <paul@xen.org>,
George Dunlap <George.Dunlap@eu.citrix.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Ian Jackson <ian.jackson@citrix.com>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Subject: Re: [PATCH v2 1/7] x86: fix compat header generation
Date: Wed, 1 Jul 2020 18:10:57 +0200 [thread overview]
Message-ID: <20200701161057.GV735@Air-de-Roger> (raw)
In-Reply-To: <a8139d0e-f332-b877-dea8-3ce8a6869285@suse.com>
On Wed, Jul 01, 2020 at 12:25:15PM +0200, Jan Beulich wrote:
> As was pointed out by 0e2e54966af5 ("mm: fix public declaration of
> struct xen_mem_acquire_resource"), we're not currently handling structs
> correctly that have uint64_aligned_t fields. #pragma pack(4) suppresses
> the necessary alignment even if the type did properly survive (which
> it also didn't) in the process of generating the headers. Overall,
> with the above mentioned change applied, there's only a latent issue
> here afaict, i.e. no other of our interface structs is currently
> affected.
>
> As a result it is clear that using #pragma pack(4) is not an option.
> Drop all uses from compat header generation. Make sure
> {,u}int64_aligned_t actually survives, such that explicitly aligned
> fields will remain aligned. Arrange for {,u}int64_t to be transformed
> into a type that's 64 bits wide and 4-byte aligned, by utilizing that
> in typedef-s the "aligned" attribute can be used to reduce alignment.
> Additionally, for the cases where native structures get re-used,
> enforce suitable alignment via typedef-s (which allow alignment to be
> reduced).
>
> This use of typedef-s makes necessary changes to CHECK_*() macro
> generation: Previously get-fields.sh relied on finding struct/union
> keywords when other compound types were used. We now need to use the
> typedef-s (guaranteeing suitable alignment) now, and hence the script
Extra now before the comma I think.
> has to recognize those cases, too. (Unfortunately there are a few
> special cases to be dealt with, but this is really not much different
> from e.g. the pre-existing compat_domain_handle_t special case.)
>
> This need to use typedef-s is certainly somewhat fragile going forward,
> as in similar future cases it is imperative to also use typedef-s, or
> else the CHECK_*() macros won't check what they're supposed to check. I
> don't currently see any means to avoid this fragility, though.
>
> There's one change to generated code according to my observations: In
> arch_compat_vcpu_op() the runstate area "area" variable would previously
> have been put in a just 4-byte aligned stack slot (despite being 8 bytes
> in size), whereas now it gets put in an 8-byte aligned location.
>
> There also results some curious inconsistency in struct xen_mc from
> these changes - I intend to clean this up later on. Otherwise unrelated
> code would also need adjustment right here.
Oh, so that's the reason fields in xen_mc are not all switched to use
their typedef equivalent I guess?
> --- a/xen/tools/get-fields.sh
> +++ b/xen/tools/get-fields.sh
> @@ -418,6 +418,21 @@ check_field ()
> "}")
> level=$(expr $level - 1) id=
> ;;
> + compat_*_t)
> + if [ $level = 2 ]
> + then
> + fields=" "
> + token="${token%_t}"
> + token="${token#compat_}"
> + fi
> + ;;
> + evtchn_*_compat_t)
> + if [ $level = 2 -a $token != evtchn_port_compat_t ]
> + then
> + fields=" "
> + token="${token%_compat_t}"
> + fi
> + ;;
Likely related to the above, but I assume we might want to add a check
here to assert no struct fields are used?
I assume this is not added here in order to prevent exploding due to
the xen_mc issues.
Thanks, Roger.
next prev parent reply other threads:[~2020-07-01 16:11 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-01 10:22 [PATCH v2 0/7] x86: compat header generation and checking adjustments Jan Beulich
2020-07-01 10:25 ` [PATCH v2 1/7] x86: fix compat header generation Jan Beulich
2020-07-01 16:10 ` Roger Pau Monné [this message]
2020-07-01 16:17 ` Jan Beulich
2020-07-15 8:43 ` Roger Pau Monné
2020-07-15 8:56 ` Jan Beulich
2020-07-01 10:25 ` [PATCH v2 2/7] x86/mce: add compat struct checking for XEN_MC_inject_v2 Jan Beulich
2020-07-14 10:24 ` Roger Pau Monné
2020-07-14 11:44 ` Jan Beulich
2020-07-14 14:30 ` Roger Pau Monné
2020-07-01 10:26 ` [PATCH v2 3/7] x86/mce: bring hypercall subop compat checking in sync again Jan Beulich
2020-07-14 11:19 ` Roger Pau Monné
2020-07-14 11:47 ` Jan Beulich
2020-07-14 14:31 ` Roger Pau Monné
2020-07-15 6:27 ` Jan Beulich
2020-07-14 14:32 ` Roger Pau Monné
2020-07-01 10:27 ` [PATCH v2 4/7] x86/dmop: add compat struct checking for XEN_DMOP_map_mem_type_to_ioreq_server Jan Beulich
2020-07-14 11:19 ` Roger Pau Monné
2020-07-01 10:27 ` [PATCH v2 5/7] x86: generalize padding field handling Jan Beulich
2020-07-14 14:29 ` Roger Pau Monné
2020-07-15 6:36 ` Jan Beulich
2020-07-15 8:34 ` Roger Pau Monné
2020-07-15 8:47 ` Jan Beulich
2020-07-01 10:28 ` [PATCH v2 6/7] flask: drop dead compat translation code Jan Beulich
2020-07-14 14:58 ` Roger Pau Monné
2020-07-15 6:42 ` Jan Beulich
2020-07-15 8:41 ` Roger Pau Monné
2020-07-15 8:52 ` Jan Beulich
2020-07-15 10:08 ` Roger Pau Monné
2020-07-01 10:28 ` [PATCH v2 7/7] x86: only generate compat headers actually needed Jan Beulich
2020-07-14 15:03 ` Roger Pau Monné
2020-07-15 6:47 ` Jan Beulich
2020-07-02 7:34 ` [PATCH v2 0/7] x86: compat header generation and checking adjustments Paul Durrant
2020-07-02 7:42 ` Jan Beulich
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