Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

[Linus Torvalds]

[-- Attachment #1: Type: text/plain, Size: 1152 bytes --]

On Sat, May 28, 2022 at 10:40 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> So digging a bit deeper - since I have am arm compiler after all - I
> note that 'sizeof(detailed_timings)' is 88.

Hmm.

sizeof() both

    detailed_timings[0].data.other_data.data.range.formula.gtf2

and

    detailed_timings[0].data.other_data.data.range.formula.cvt

is 7.

But the *union* of those things is

    detailed_timings[0].data.other_data.data.range.formula

and its size is 8 (despite having an alignment of just 1).

The attached patch would seem to fix it for me.

Not very much tested, and I have no idea what it is that triggers this
only on spear3xx_defconfig.

Some ARM ABI issue that is triggered by some very particular ARM
compiler flag enabled by that config?

Adding some ARM (and SPEAR, and SoC) people in case they have any idea.

This smells like a compiler bug triggered by "there's a 16-bit member
field in that gtf2 structure, and despite it being packed and aligned
to 1, we somehow still align the size to 2".

I dunno. But marking those unions packed too doesn't seem wrong, and
does seem to fix it.

                  Linus

[-- Attachment #2: patch.diff --]
[-- Type: text/x-patch, Size: 1024 bytes --]

 include/drm/drm_edid.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/drm/drm_edid.h b/include/drm/drm_edid.h
index c3204a58fb09..b2756753370b 100644
--- a/include/drm/drm_edid.h
+++ b/include/drm/drm_edid.h
@@ -121,7 +121,7 @@ struct detailed_data_monitor_range {
 			u8 supported_scalings;
 			u8 preferred_refresh;
 		} __attribute__((packed)) cvt;
-	} formula;
+	} __attribute__((packed)) formula;
 } __attribute__((packed));
 
 struct detailed_data_wpindex {
@@ -154,7 +154,7 @@ struct detailed_non_pixel {
 		struct detailed_data_wpindex color;
 		struct std_timing timings[6];
 		struct cvt_timing cvt[4];
-	} data;
+	} __attribute__((packed)) data;
 } __attribute__((packed));
 
 #define EDID_DETAIL_EST_TIMINGS 0xf7
@@ -172,7 +172,7 @@ struct detailed_timing {
 	union {
 		struct detailed_pixel_timing pixel_data;
 		struct detailed_non_pixel other_data;
-	} data;
+	} __attribute__((packed)) data;
 } __attribute__((packed));
 
 #define DRM_EDID_INPUT_SERRATION_VSYNC (1 << 0)

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Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

[Arnd Bergmann]

On Sat, May 28, 2022 at 8:08 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> Not very much tested, and I have no idea what it is that triggers this
> only on spear3xx_defconfig.
>
> Some ARM ABI issue that is triggered by some very particular ARM
> compiler flag enabled by that config?

It's CONFIG_ARM_AEABI, which is normally set everywhere. Without this
option, you the kernel is built for the old 'OABI' that forces all non-packed
struct members to be at least 16-bit aligned.

I think Russell still uses OABI kernels on his oldest machines, but it is
incompatible with all modern user space and should probably not be
in the defconfig.

Your patch looks like the correct solution to me.

      Arnd

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Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

[Linus Torvalds]

On Sat, May 28, 2022 at 11:59 AM Arnd Bergmann <arnd@arndb.de> wrote:
>
> It's CONFIG_ARM_AEABI, which is normally set everywhere. Without this
> option, you the kernel is built for the old 'OABI' that forces all non-packed
> struct members to be at least 16-bit aligned.

Looks like forced word (32 bit) alignment to me.

I wonder how many other structures that messes up, but I committed the
EDID fix for now.

This has presumably been broken for a long time, but maybe the
affected targets don't typically use EDID and kernel modesetting, and
only use some fixed display setup instead.

Those structure definitions go back a _loong_ time (from a quick 'git
blame' I see November 2008).

But despite that, I did not mark my fix 'cc:stable' because I don't
know if any of those machines affected by this bad arm ABI issue could
possibly care.

At least my tree hopefully now builds on them, with the BUILD_BUG_ON()
that uncovered this.

                   Linus

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Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

[Arnd Bergmann]

On Sat, May 28, 2022 at 10:31 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Sat, May 28, 2022 at 11:59 AM Arnd Bergmann <arnd@arndb.de> wrote:
> >
> > It's CONFIG_ARM_AEABI, which is normally set everywhere. Without this
> > option, you the kernel is built for the old 'OABI' that forces all non-packed
> > struct members to be at least 16-bit aligned.
>
> Looks like forced word (32 bit) alignment to me.

Ah, of course, I keep mixing it up with the odd structure alignment of m68k,
which does the opposite and aligns struct members to no more than 16 bits.

        Arnd

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Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

[Jani Nikula]

On Sat, 28 May 2022, Linus Torvalds <torvalds@linux-foundation.org> wrote:
> On Sat, May 28, 2022 at 11:59 AM Arnd Bergmann <arnd@arndb.de> wrote:
>>
>> It's CONFIG_ARM_AEABI, which is normally set everywhere. Without this
>> option, you the kernel is built for the old 'OABI' that forces all non-packed
>> struct members to be at least 16-bit aligned.
>
> Looks like forced word (32 bit) alignment to me.
>
> I wonder how many other structures that messes up, but I committed the
> EDID fix for now.

Thanks for the fix, and the thorough commit message!

> This has presumably been broken for a long time, but maybe the
> affected targets don't typically use EDID and kernel modesetting, and
> only use some fixed display setup instead.
>
> Those structure definitions go back a _loong_ time (from a quick 'git
> blame' I see November 2008).
>
> But despite that, I did not mark my fix 'cc:stable' because I don't
> know if any of those machines affected by this bad arm ABI issue could
> possibly care.
>
> At least my tree hopefully now builds on them, with the BUILD_BUG_ON()
> that uncovered this.

Indeed the bug is ancient. I just threw in the BUILD_BUG_ON() on a whim
as an extra sanity check when doing pointer arithmetics on struct edid
*.

If there are affected machines, buffer overflows are the real danger due
to edid->extensions indicating the number of extensions.


BR,
Jani.

-- 
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Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

[Jani Nikula]

On Mon, 30 May 2022, Jani Nikula <jani.nikula@intel.com> wrote:
> On Sat, 28 May 2022, Linus Torvalds <torvalds@linux-foundation.org> wrote:
>> On Sat, May 28, 2022 at 11:59 AM Arnd Bergmann <arnd@arndb.de> wrote:
>>>
>>> It's CONFIG_ARM_AEABI, which is normally set everywhere. Without this
>>> option, you the kernel is built for the old 'OABI' that forces all non-packed
>>> struct members to be at least 16-bit aligned.
>>
>> Looks like forced word (32 bit) alignment to me.
>>
>> I wonder how many other structures that messes up, but I committed the
>> EDID fix for now.
>
> Thanks for the fix, and the thorough commit message!
>
>> This has presumably been broken for a long time, but maybe the
>> affected targets don't typically use EDID and kernel modesetting, and
>> only use some fixed display setup instead.
>>
>> Those structure definitions go back a _loong_ time (from a quick 'git
>> blame' I see November 2008).
>>
>> But despite that, I did not mark my fix 'cc:stable' because I don't
>> know if any of those machines affected by this bad arm ABI issue could
>> possibly care.
>>
>> At least my tree hopefully now builds on them, with the BUILD_BUG_ON()
>> that uncovered this.
>
> Indeed the bug is ancient. I just threw in the BUILD_BUG_ON() on a whim
> as an extra sanity check when doing pointer arithmetics on struct edid
> *.
>
> If there are affected machines, buffer overflows are the real danger due
> to edid->extensions indicating the number of extensions.

That is, for EDID. Makes you wonder about all the other packed structs
with enum members across the kernel.

BR,
Jani.


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Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

[Arnd Bergmann]

On Mon, May 30, 2022 at 11:33 AM Jani Nikula <jani.nikula@intel.com> wrote:
>
> That is, for EDID. Makes you wonder about all the other packed structs
> with enum members across the kernel.

It is not the 'enum' that is special here, it's the 'union' having
unpacked members,
and the same thing happens when you have nested structs: both the inner
and the outer aggregate need to be packed, either with __packed at the
end, or on each individual member that is not fully aligned to
max(sizeof(member), 4)).

I think in general, most __packed annotations we have in the kernel are
completely pointless because they do not change the structure layout on
any architecture but instead just make member access slower on
architectures that lack unaligned load/store instructions. There have
definitely been other cases though where a __packed annotation is
not needed on any sane architecture but is needed for OABI ARM.

Overall I'm not that worried because the only machines running OABI
kernels would be on really old hardware that runs a limited set of
driver code.

A completely different matter are the extraneous __packed annotations
that lead to possible problems when accessed through a misaligned
pointer. We ignore -Waddress-of-packed-member and -Wcast-align
in the kernel, so these never get caught at build time, but we have
seen bugs from gcc making incorrect assumptions about alignment
even on architectures that have unaligned load/store instructions.

      Arnd

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Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

[Jani Nikula]

On Mon, 30 May 2022, Arnd Bergmann <arnd@arndb.de> wrote:
> On Mon, May 30, 2022 at 11:33 AM Jani Nikula <jani.nikula@intel.com> wrote:
>>
>> That is, for EDID. Makes you wonder about all the other packed structs
>> with enum members across the kernel.
>
> It is not the 'enum' that is special here, it's the 'union' having
> unpacked members,

Obviously meant union not enum, that was just a -ENOCOFFEE on my part.

> and the same thing happens when you have nested structs: both the inner
> and the outer aggregate need to be packed, either with __packed at the
> end, or on each individual member that is not fully aligned to
> max(sizeof(member), 4)).
>
> I think in general, most __packed annotations we have in the kernel are
> completely pointless because they do not change the structure layout on
> any architecture but instead just make member access slower on

Please explain.

They are used quite a bit for parsing blob data, or
serialization/deserialization, like in the EDID case at hand. Try
removing __attribute__((packed)) from include/drm/drm_edid.h and see the
sizeof(struct edid) on any architecture.

BR,
Jani.

> architectures that lack unaligned load/store instructions. There have
> definitely been other cases though where a __packed annotation is
> not needed on any sane architecture but is needed for OABI ARM.
>
> Overall I'm not that worried because the only machines running OABI
> kernels would be on really old hardware that runs a limited set of
> driver code.
>
> A completely different matter are the extraneous __packed annotations
> that lead to possible problems when accessed through a misaligned
> pointer. We ignore -Waddress-of-packed-member and -Wcast-align
> in the kernel, so these never get caught at build time, but we have
> seen bugs from gcc making incorrect assumptions about alignment
> even on architectures that have unaligned load/store instructions.
>
>       Arnd

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Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

[Arnd Bergmann]

On Mon, May 30, 2022 at 3:10 PM Jani Nikula <jani.nikula@intel.com> wrote:
> >
> > I think in general, most __packed annotations we have in the kernel are
> > completely pointless because they do not change the structure layout on
> > any architecture but instead just make member access slower on
>
> Please explain.
>
> They are used quite a bit for parsing blob data, or
> serialization/deserialization, like in the EDID case at hand. Try
> removing __attribute__((packed)) from include/drm/drm_edid.h and see the
> sizeof(struct edid) on any architecture.

The annotations for edid are completely correct and necessary. However
other driver authors just slap __packed annotations on any structure
even if the layout is not fixed at all like:

struct my_driver_priv {
       struct device dev;
       u8 causes_misalignment;
       spinlock_t lock;
       atomic_t counter;
} __packed; /* this annotation is harmful because it breaks the atomics */

or if the annotation does not change the layout like

struct my_dma_descriptor {
     __le64 address;
     __le64 length;
} __packed; /* does not change layout but makes access slow on some
architectures */

       Arnd

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Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

[Jani Nikula]

On Mon, 30 May 2022, Arnd Bergmann <arnd@arndb.de> wrote:
> On Mon, May 30, 2022 at 3:10 PM Jani Nikula <jani.nikula@intel.com> wrote:
>> >
>> > I think in general, most __packed annotations we have in the kernel are
>> > completely pointless because they do not change the structure layout on
>> > any architecture but instead just make member access slower on
>>
>> Please explain.
>>
>> They are used quite a bit for parsing blob data, or
>> serialization/deserialization, like in the EDID case at hand. Try
>> removing __attribute__((packed)) from include/drm/drm_edid.h and see the
>> sizeof(struct edid) on any architecture.
>
> The annotations for edid are completely correct and necessary. However
> other driver authors just slap __packed annotations on any structure
> even if the layout is not fixed at all like:

Right. Thanks for the examples.

> struct my_driver_priv {
>        struct device dev;
>        u8 causes_misalignment;
>        spinlock_t lock;
>        atomic_t counter;
> } __packed; /* this annotation is harmful because it breaks the atomics */

I wonder if this is something that could be caught with coccinelle. Or
sparse. Are there any cases where this combo is necessary? (I can't
think of any, but it's a low bar. ;)

Cc: Julia.

> or if the annotation does not change the layout like
>
> struct my_dma_descriptor {
>      __le64 address;
>      __le64 length;
> } __packed; /* does not change layout but makes access slow on some
> architectures */

Why is this the case, though? I'd imagine the compiler could figure this
out.


BR,
Jani.

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Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

[Arnd Bergmann]

On Mon, May 30, 2022 at 4:08 PM Jani Nikula <jani.nikula@intel.com> wrote:
> On Mon, 30 May 2022, Arnd Bergmann <arnd@arndb.de> wrote:
> > struct my_driver_priv {
> >        struct device dev;
> >        u8 causes_misalignment;
> >        spinlock_t lock;
> >        atomic_t counter;
> > } __packed; /* this annotation is harmful because it breaks the atomics */
>
> I wonder if this is something that could be caught with coccinelle. Or
> sparse. Are there any cases where this combo is necessary? (I can't
> think of any, but it's a low bar. ;)
>
> Cc: Julia.

I think one would first have to make a list of data types that are not
meant to be in a packed structure. It could be a good start to
search for any packed aggregates with a pointer, atomic_t or spinlock_t
in them, but there are of course many more types that you won't
find in hardware structures.

> > or if the annotation does not change the layout like
> >
> > struct my_dma_descriptor {
> >      __le64 address;
> >      __le64 length;
> > } __packed; /* does not change layout but makes access slow on some
> > architectures */
>
> Why is this the case, though? I'd imagine the compiler could figure this
> out.

When you annotate the entire structure as __packed without an
extra __aligned() annotation, the compiler has to assume that the
structure itself is unaligned as well. On many of the older architectures,
this will result in accessing the values one byte at a time. Marking
the structure as "__packed __aligned(8)" instead would be harmless.

When I have a structure with a few misaligned members, I generally
prefer to only annotate the members that are not naturally aligned,
but this approach is not very common.

         Arnd

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Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

[Julia Lawall]

> On 30 May 2022, at 15:27, Arnd Bergmann <arnd@arndb.de> wrote:
> 
> On Mon, May 30, 2022 at 4:08 PM Jani Nikula <jani.nikula@intel.com> wrote:
>>> On Mon, 30 May 2022, Arnd Bergmann <arnd@arndb.de> wrote:
>>> struct my_driver_priv {
>>>       struct device dev;
>>>       u8 causes_misalignment;
>>>       spinlock_t lock;
>>>       atomic_t counter;
>>> } __packed; /* this annotation is harmful because it breaks the atomics */
>> 
>> I wonder if this is something that could be caught with coccinelle. Or
>> sparse. Are there any cases where this combo is necessary? (I can't
>> think of any, but it's a low bar. ;)
>> 
>> Cc: Julia.
> 
> I think one would first have to make a list of data types that are not
> meant to be in a packed structure. It could be a good start to
> search for any packed aggregates with a pointer, atomic_t or spinlock_t
> in them, but there are of course many more types that you won't
> find in hardware structures.
> 
>>> or if the annotation does not change the layout like
>>> 
>>> struct my_dma_descriptor {
>>>     __le64 address;
>>>     __le64 length;
>>> } __packed; /* does not change layout but makes access slow on some
>>> architectures */
>> 
>> Why is this the case, though? I'd imagine the compiler could figure this
>> out.
> 
> When you annotate the entire structure as __packed without an
> extra __aligned() annotation, the compiler has to assume that the
> structure itself is unaligned as well. On many of the older architectures,
> this will result in accessing the values one byte at a time. Marking
> the structure as "__packed __aligned(8)" instead would be harmless.
> 
> When I have a structure with a few misaligned members, I generally
> prefer to only annotate the members that are not naturally aligned,
> but this approach is not very common.

Searching for specific types in a packed structure would be easy.

Coccinelle could duplicate the structure without the packed and see if any offsets change, using build bug on, but that would be architecture specific so maybe not useful.

Julia



>         Arnd


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Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

[Arnd Bergmann]

On Tue, May 31, 2022 at 8:26 AM Julia Lawall <Julia.Lawall@inria.fr> wrote:
> > On 30 May 2022, at 15:27, Arnd Bergmann <arnd@arndb.de> wrote:
> > On Mon, May 30, 2022 at 4:08 PM Jani Nikula <jani.nikula@intel.com> wrote:
> >>> On Mon, 30 May 2022, Arnd Bergmann <arnd@arndb.de> wrote:
> >>> struct my_driver_priv {
> >>>       struct device dev;
> >>>       u8 causes_misalignment;
> >>>       spinlock_t lock;
> >>>       atomic_t counter;
> >>> } __packed; /* this annotation is harmful because it breaks the atomics */
> >>
> >> I wonder if this is something that could be caught with coccinelle. Or
> >> sparse. Are there any cases where this combo is necessary? (I can't
> >> think of any, but it's a low bar. ;)
> >>
...
> >>> or if the annotation does not change the layout like
> >>>
> >>> struct my_dma_descriptor {
> >>>     __le64 address;
> >>>     __le64 length;
> >>> } __packed; /* does not change layout but makes access slow on some
> >>> architectures */
> >>
> >> Why is this the case, though? I'd imagine the compiler could figure this
> >> out.
> >
> > When you annotate the entire structure as __packed without an
> > extra __aligned() annotation, the compiler has to assume that the
> > structure itself is unaligned as well. On many of the older architectures,
> > this will result in accessing the values one byte at a time. Marking
> > the structure as "__packed __aligned(8)" instead would be harmless.
> >
> > When I have a structure with a few misaligned members, I generally
> > prefer to only annotate the members that are not naturally aligned,
> > but this approach is not very common.
>
> Searching for specific types in a packed structure would be easy.

As an experiment: what kind of results would we get when looking
for packed structures and unions that contain any of these:

- spinlock_t
- atomic_t
- dma_addr_t
- phys_addr_t
- size_t
- any pointer
- any enum
- struct mutex
- struct device

This is just a list of common data types that are used in a lot of
structures but that one should never find in hardware specific
types. If the output from coccinelle is 90% actual bugs, this would
be really helpful. OTOH if there is no output at all, or all
false-positives, we don't need to look for additional types.

> Coccinelle could duplicate the structure without the packed and see if
> any offsets change, using build bug on, but that would be architecture
> specific so maybe not useful.

I would consider this a separate issue. The first one above is for identifying
structures that are marked as packed but should not be packed at
all, regardless of whether that changes the layout.

       Arnd

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Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

[Linus Torvalds]

On Tue, May 31, 2022 at 1:04 AM Arnd Bergmann <arnd@arndb.de> wrote:
>
> As an experiment: what kind of results would we get when looking
> for packed structures and unions that contain any of these:

Yeah, any atomics or locks should always be aligned, and won't even
work (or might be *very* slow) on multiple architectures. Even x86 -
which does very well on unaligned data - reacts badly to sufficiently
unaligned atomics (ie cacheline crossing).

I don't think we have that. Not only because it would already cause
breakage, but simply because the kinds of structures that people pack
aren't generally the kind that contain these kinds of things.

That said, you might have a struct that is packed, but that
intentionally aligns parts of itself, so it *could* be valid.

But it would probably not be a bad idea to check that packed
structures/unions don't have atomic types or locks in them. I _think_
we're all good, but who knows..

            Linus

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Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

[Keisuke Nishimura]

On 2022/06/01 1:41, Linus Torvalds wrote:
> On Tue, May 31, 2022 at 1:04 AM Arnd Bergmann <arnd@arndb.de> wrote:
>>
>> As an experiment: what kind of results would we get when looking
>> for packed structures and unions that contain any of these:
> 

> I don't think we have that. Not only because it would already cause
> breakage, but simply because the kinds of structures that people pack
> aren't generally the kind that contain these kinds of things.
> 
> That said, you might have a struct that is packed, but that
> intentionally aligns parts of itself, so it *could* be valid.
> 
> But it would probably not be a bad idea to check that packed
> structures/unions don't have atomic types or locks in them. I _think_
> we're all good, but who knows..


I am Julia's student at INRIA and I heard from her that there is an 
opportunity to use Coccinelle to find specific types in packed struct or
enum.

I found 13 definitions of packed structure that contains:
 > - spinlock_t
 > - atomic_t
 > - dma_addr_t
 > - phys_addr_t
 > - size_t

 > - struct mutex
 > - struct device

- raw_spinlock_t

== Results ==
security/tomoyo/common.h: atomic_t in tomoyo_shared_acl_head
drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls.h: spinlock_t in 
key_map
include/linux/ti-emif-sram.h: phys_addr_t in ti_emif_pm_data
drivers/scsi/wd719x.h: dma_addr_t in wd719x_scb
drivers/net/wireless/intel/ipw2x00/ipw2200.h: dma_addr_t in clx2_queue
drivers/infiniband/hw/irdma/osdep.h: dma_addr_t in irdma_dma_mem
drivers/infiniband/core/mad_priv.h: size_t in ib_mad_private
drivers/crypto/qat/qat_common/qat_asym_algs.c:
- dma_addr_t in qat_rsa_ctx
- dma_addr_t in qat_dh_ctx
drivers/atm/idt77252.h: dma_addr_t in idt77252_skb_prv
arch/s390/include/asm/kvm_host.h: atomic_t in kvm_s390_sie_block

drivers/net/wireless/ath/ath10k/core.h: dma_addr_t in ath10k_skb_cb
drivers/net/wireless/ath/ath11k/core.h: dma_addr_t in ath10k_skb_cb
drivers/crypto/ccp/ccp-dev.h: dma_addr_t in ccp_dma_info

The last 3 structures have a dma_adddr_t member defined as the first 
member variable. Most of the others also seems valid.

I used this SmPL script to find them:

@e1@
type T;
identifier i;
position p;
attribute name __packed;
@@
  T@p  {
   ...
(
   atomic_t i;
|
   raw_spinlock_t i;
|
   struct mutex i;
|
   spinlock_t i;
|
   dma_addr_t i;
|
   phys_addr_t i;
|
   size_t i;
|
  struct device i;
)
   ...
  }
  __packed;

@e2@
type T;
identifier i;
position p;
@@
  T@p  {
   ...
(
   atomic_t i;
|
   raw_spinlock_t i;
|
   struct mutex i;
|
   spinlock_t i;
|
   dma_addr_t i;
|
   phys_addr_t i;
|
   size_t i;
|
  struct device i;
)
   ...
  }
    __attribute__((
(
  pack
|
  __pack__
)
  ,... ));

@script:python@
ps <<e1.p;
@@
for p in ps:
   print p.file, p.line
@script:python@
ps <<e2.p;
@@
for p in ps:
   print p.file, p.line


Keisuke

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Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

[Linus Torvalds]

On Wed, Jun 1, 2022 at 3:28 PM Keisuke Nishimura
<keisuke.nishimura@inria.fr> wrote:
>
>
> I found 13 definitions of packed structure that contains:
>  > - spinlock_t
>  > - atomic_t
>  > - dma_addr_t
>  > - phys_addr_t
>  > - size_t
>  > - struct mutex
>  > - struct device
>
> - raw_spinlock_t

Ok, so I don't think dma_addr_t/phys_addr_t/size_t are problematic,
they are just regular integers.

And 'struct device' is problematic only as it then contains any of the
atomic types (which it does)

> security/tomoyo/common.h: atomic_t in tomoyo_shared_acl_head
> drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls.h: spinlock_t in key_map
> arch/s390/include/asm/kvm_host.h: atomic_t in kvm_s390_sie_block

So these do look problematic.

I'm not actually clear on why tomoyo_shared_acl_head would be packed.
That makes no sense to me.

Same goes for key_map, it's not clear what the reason for that
__packed is, and it's clearly bogus. It might work, almost by mistake,
but it's wrong to try to pack that spinlock_t.

The s390 kvm use actually looks fine: the structure is packed, but
it's also aligned, and the spin-lock is at the beginning, so the
"packing" part is about the other members, not the first one.

The two that look wrong look like they will probably work anyway
(they'll presumably be effectively word-aligned, and that's sufficient
for spinlocks in practice).

But let's cc the tomoyo and chelsio people.

                 Linus

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Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

[Arnd Bergmann]

On Thu, Jun 2, 2022 at 3:08 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> On Wed, Jun 1, 2022 at 3:28 PM Keisuke Nishimura
> <keisuke.nishimura@inria.fr> wrote:
> >
> >
> > I found 13 definitions of packed structure that contains:
> >  > - spinlock_t
> >  > - atomic_t
> >  > - dma_addr_t
> >  > - phys_addr_t
> >  > - size_t
> >  > - struct mutex
> >  > - struct device
> >
> > - raw_spinlock_t
>
> Ok, so I don't think dma_addr_t/phys_addr_t/size_t are problematic,
> they are just regular integers.
>
> And 'struct device' is problematic only as it then contains any of the
> atomic types (which it does)
is
I suggested this list because they are problematic for different reasons:

- any atomics are clearly broken here

- dma_addr_t/phys_addr_t are sometimes put into hardware data
  structures in coherent DMA allocations. This is broken because these
  types are variably-sized depending on the architecture, and annotating
  structures in uncached memory as __packed is also broken on
  architectures that have neither coherent DMA nor unaligned access
  (most 32-bit mips and armv5), where this will result in a series of
  expensive one-byte uncached load/store instructions.

- having any complex kernel data structure embedded in a __packed
  struct is a red flag, because there should not be a need to mark
  it packed for compatibility with either hardware or user space.
  If the structure is actually misaligned, passing a pointer for the
  embedded struct into an interface that expects an aligned pointer
  is undefined behavior in C, and gcc may decide to do something
  bad here even on architectures that can access unaligned
  pointers.

> > security/tomoyo/common.h: atomic_t in tomoyo_shared_acl_head
> > drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls.h: spinlock_t in key_map
> > arch/s390/include/asm/kvm_host.h: atomic_t in kvm_s390_sie_block
>
> So these do look problematic.
>
> I'm not actually clear on why tomoyo_shared_acl_head would be packed.
> That makes no sense to me.
>
> Same goes for key_map, it's not clear what the reason for that
> __packed is, and it's clearly bogus. It might work, almost by mistake,
> but it's wrong to try to pack that spinlock_t.
>
> The s390 kvm use actually looks fine: the structure is packed, but
> it's also aligned, and the spin-lock is at the beginning, so the
> "packing" part is about the other members, not the first one.

Right, I think the coccinelle script should nor report structures
that are both packed and aligned.

> The two that look wrong look like they will probably work anyway
> (they'll presumably be effectively word-aligned, and that's sufficient
> for spinlocks in practice).
>
> But let's cc the tomoyo and chelsio people.

I think both of them work because the structures are always
embedded inside of larger structures that have at least word
alignment. This is the thing I was looking for, and the
__packed attribute was added in error, most likely copied
from somewhere else.

Looking at the other ones:

include/linux/ti-emif-sram.h: phys_addr_t in ti_emif_pm_data

No misalignment because of the __aligned(8), but this
might go wrong if the emif firmware relies on the structure
layout to have a 32-bit phys_addr_t.

drivers/scsi/wd719x.h: dma_addr_t in wd719x_scb

This one is correct, as the structure has 64 bytes of
hardware data and a few members that are only accessed
by the kernel. There should still be an __aligned(8)
for efficiency.

drivers/net/wireless/intel/ipw2x00/ipw2200.h: dma_addr_t in clx2_queue

Al marked the incorrect __packed annotations in 2008,
see 83f7d57c37e8 ("ipw2200 annotations and fixes").
Mostly harmless but the __packed should just get removed here.

> drivers/infiniband/hw/irdma/osdep.h: dma_addr_t in irdma_dma_mem
> drivers/infiniband/core/mad_priv.h: size_t in ib_mad_private

Same here: harmless but __packed should be removed, possibly
while reordering members by size.

> drivers/crypto/qat/qat_common/qat_asym_algs.c:
> - dma_addr_t in qat_rsa_ctx
> - dma_addr_t in qat_dh_ctx

Probably harmless because the structure is __aligned(64), but I'm
completely puzzled by what the author was actually trying to
achieve here. There are also 'bool' members in the packed struct,
which is probably something we want to look for as well.

> drivers/atm/idt77252.h: dma_addr_t in idt77252_skb_prv

This is a bug on architectures with 64-bit dma_addr_t, it should
be an __le32, and the structure should be __aligned() as a DMA
descriptor.

> drivers/net/wireless/ath/ath10k/core.h: dma_addr_t in ath10k_skb_cb
> drivers/net/wireless/ath/ath11k/core.h: dma_addr_t in ath10k_skb_cb

Should almost certainly not be __packed, fixing these will
likely improve performance on mips32 routers using ath10k

> drivers/crypto/ccp/ccp-dev.h: dma_addr_t in ccp_dma_info

This looks ok, the "__packed __aligned(4)" here can save
a bit of stack space as intended.

I think that SmPL script worked great, almost every instance is
something that ought to be changed, as long as it stops reporting
those structures that are also __aligned(). I would extend it to
also report structures with 'bool', 'enum', or any pointer, but that
could give more false-positives. Maybe have a separate script
for those instances embedding atomics or spinlocks (very broken)
vs the other members (causes more harm than good or might
need alignment).

       Arnd

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Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

[Tetsuo Handa]

On 2022/06/02 16:38, Arnd Bergmann wrote:
>> But let's cc the tomoyo and chelsio people.
> 
> I think both of them work because the structures are always
> embedded inside of larger structures that have at least word
> alignment. This is the thing I was looking for, and the
> __packed attribute was added in error, most likely copied
> from somewhere else.

The __packed in "struct tomoyo_shared_acl_head" is to embed next
naturally-aligned member of a larger struct into the bytes that
would have been wasted if __packed is not specified. For example,

struct tomoyo_shared_acl_head {
        struct list_head list;
        atomic_t users;
} __packed;

struct tomoyo_condition {
        struct tomoyo_shared_acl_head head;
        u32 size; /* Memory size allocated for this entry. */
	(...snipped...)
};

saves 4 bytes on 64 bits build.

If the next naturally-aligned member of a larger struct is larger than
the bytes that was saved by __packed, the saved bytes will be unused.

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Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

[Arnd Bergmann]

On Thu, Jun 2, 2022 at 1:21 PM Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> wrote:
> On 2022/06/02 16:38, Arnd Bergmann wrote:
> >> But let's cc the tomoyo and chelsio people.
> >
> > I think both of them work because the structures are always
> > embedded inside of larger structures that have at least word
> > alignment. This is the thing I was looking for, and the
> > __packed attribute was added in error, most likely copied
> > from somewhere else.
>
> The __packed in "struct tomoyo_shared_acl_head" is to embed next
> naturally-aligned member of a larger struct into the bytes that
> would have been wasted if __packed is not specified. For example,
>
> struct tomoyo_shared_acl_head {
>         struct list_head list;
>         atomic_t users;
> } __packed;
>
> struct tomoyo_condition {
>         struct tomoyo_shared_acl_head head;
>         u32 size; /* Memory size allocated for this entry. */
>         (...snipped...)
> };
>
> saves 4 bytes on 64 bits build.
>
> If the next naturally-aligned member of a larger struct is larger than
> the bytes that was saved by __packed, the saved bytes will be unused.

Ok, got it. I think as gcc should still be able to always figure out the
alignment when accessing the atomic, without ever falling back
to byte access on an atomic_get() or atomic_set().

To be on the safe side, I would still either move the __packed attribute
to the 'list' member, or make the structure '__aligned(4)'.

       Arnd

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Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

[Ard Biesheuvel]

On Thu, 2 Jun 2022 at 14:12, Arnd Bergmann <arnd@arndb.de> wrote:
>
> On Thu, Jun 2, 2022 at 1:21 PM Tetsuo Handa
> <penguin-kernel@i-love.sakura.ne.jp> wrote:
> > On 2022/06/02 16:38, Arnd Bergmann wrote:
> > >> But let's cc the tomoyo and chelsio people.
> > >
> > > I think both of them work because the structures are always
> > > embedded inside of larger structures that have at least word
> > > alignment. This is the thing I was looking for, and the
> > > __packed attribute was added in error, most likely copied
> > > from somewhere else.
> >
> > The __packed in "struct tomoyo_shared_acl_head" is to embed next
> > naturally-aligned member of a larger struct into the bytes that
> > would have been wasted if __packed is not specified. For example,
> >
> > struct tomoyo_shared_acl_head {
> >         struct list_head list;
> >         atomic_t users;
> > } __packed;
> >
> > struct tomoyo_condition {
> >         struct tomoyo_shared_acl_head head;
> >         u32 size; /* Memory size allocated for this entry. */
> >         (...snipped...)
> > };
> >
> > saves 4 bytes on 64 bits build.
> >
> > If the next naturally-aligned member of a larger struct is larger than
> > the bytes that was saved by __packed, the saved bytes will be unused.
>
> Ok, got it. I think as gcc should still be able to always figure out the
> alignment when accessing the atomic, without ever falling back
> to byte access on an atomic_get() or atomic_set().
>
> To be on the safe side, I would still either move the __packed attribute
> to the 'list' member, or make the structure '__aligned(4)'.
>

The tomoyo code generates lots of byte size accesses when built for
ARMv5, but interestingly, the atomic_t accesses are emitted normally,
probably due to the fact that the C api (atomic_read, atomic_set, etc)
takes atomic_t pointers, and so GCC assumes natural alignment, even
when inlining. But ordinary accesses of multi-byte fields in the
structs in question are emitted as sequences of LDRB instructions.

I understand the reason for these annotations, but I think we should
drop them anyway, and just let the compiler organize the structs.

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Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

[Christoph Hellwig]

On Thu, Jun 02, 2022 at 09:38:56AM +0200, Arnd Bergmann wrote:
> - dma_addr_t/phys_addr_t are sometimes put into hardware data
>   structures in coherent DMA allocations.

Putting a dma_addr_t into a hardware data structure is broken.
dma_addr_t is the in-memory type, for the hardare it should always
be a __le/__be type of the actual width that the particular piece
of hardware uses.

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Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

[Keisuke Nishimura]

On 2022/06/02 16:38, Arnd Bergmann wrote:
> I think that SmPL script worked great, almost every instance is
> something that ought to be changed, as long as it stops reporting
> those structures that are also __aligned(). I would extend it to
> also report structures with 'bool', 'enum', or any pointer, but that
> could give more false-positives. Maybe have a separate script
> for those instances embedding atomics or spinlocks (very broken)
> vs the other members (causes more harm than good or might
> need alignment).

I extended my script to detect __packed struct or union without 
__aligned. It is split in two scripts.

The first one is to search for problematic cases where __packed 
structs/unions have atomic types or spinlock types. In this version, 
types whose names contain "atomic" or "spinlock" are targeted.

== Scripts ==
@r@
type T;
identifier i;
type b =~ ".*(atomic|spinlock).*";
position p;
attribute name __packed, __aligned;
attribute at;
@@
  T@p  {
    ...
   b i;
   ...
  } at;
@script:python@
p <<r.p;
T <<r.T;
b <<r.b;
a << r.at;
@@
if not "__align" in a:
   print("{}: {} in {}".format(p[0].file, b, T))


== Results ==
drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls.h: spinlock_t in 
struct key_map
security/tomoyo/common.h: atomic_t in struct tomoyo_shared_acl_head
include/rdma/ib_hdrs.h: struct {  __be32 aeth ;  __be64 atomic_ack_eth ; 
} in union ib_ehdrs
include/rdma/ib_hdrs.h: struct ib_atomic_eth in union ib_ehdrs


The second one is to check the existence of "the other members" such as 
bool, pointer types. The results seem to have a lot of false positives.

== Scripts ==
@r@
type T, T2;
identifier i, eid;
position p;
attribute name __packed, __aligned;
attribute at;
@@
  T@p  {
    ...
(
   dma_addr_t i;
|
   phys_addr_t i;
|
   size_t i;
|
   struct device i;
|
   enum eid i;
|
   enum {...} i;
|
   T2 *i;
|
   bool i;
)
   ...
  } at;
@script:python@
p <<r.p;
T <<r.T;
a << r.at;
@@
if not "__align" in a and "__packed" in a:
   print("{}: {}".format(p[0].file, T))


== Results ==
drivers/net/wireless/purelifi/plfxlc/mac.h: struct plfxlc_header
drivers/gpu/drm/amd/amdgpu/amdgpu_ras_eeprom.h: struct eeprom_table_record
drivers/net/wireless/marvell/mwifiex/fw.h: struct mwifiex_bg_scan_cfg
drivers/net/wireless/marvell/mwifiex/fw.h: struct mwifiex_user_scan_cfg
kernel/power/snapshot.c: struct linked_page
drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls.h: struct key_map
drivers/net/wireless/ti/wlcore/acx.h: struct wl1271_acx_mem_map
drivers/staging/vt6655/desc.h: struct vnt_rx_desc
drivers/staging/vt6655/desc.h: struct vnt_tx_desc
drivers/atm/idt77252.h: struct idt77252_skb_prv
drivers/scsi/myrb.h: struct myrb_enquiry
drivers/scsi/myrb.h: struct myrb_enquiry2
drivers/staging/rtl8192e/rtllib.h: struct sw_chnl_cmd
sound/soc/intel/catpt/messages.c: struct catpt_set_write_pos_input
drivers/firmware/efi/test/efi_test.h: struct efi_getnexthighmonotoniccount
drivers/firmware/efi/test/efi_test.h: struct efi_getnextvariablename
drivers/firmware/efi/test/efi_test.h: struct efi_gettime
drivers/firmware/efi/test/efi_test.h: struct efi_getvariable
drivers/firmware/efi/test/efi_test.h: struct efi_getwakeuptime
drivers/firmware/efi/test/efi_test.h: struct efi_querycapsulecapabilities
drivers/firmware/efi/test/efi_test.h: struct efi_queryvariableinfo
drivers/firmware/efi/test/efi_test.h: struct efi_resetsystem
drivers/firmware/efi/test/efi_test.h: struct efi_settime
drivers/firmware/efi/test/efi_test.h: struct efi_setvariable
drivers/firmware/efi/test/efi_test.h: struct efi_setwakeuptime
fs/cifs/cifs_ioctl.h: struct smb3_notify
sound/soc/intel/skylake/skl-topology.h: struct skl_audio_data_format
sound/soc/intel/skylake/skl-topology.h: struct skl_src_module_cfg
sound/soc/intel/skylake/skl-topology.h: struct skl_up_down_mixer_cfg
drivers/staging/rtl8192e/rtl8192e/rtl_core.h: struct tx_ring
fs/ksmbd/smb2pdu.h: struct fs_type_info
net/tipc/msg.h: struct tipc_skb_cb
drivers/net/wireless/mediatek/mt76/mt76_connac_mcu.h: struct sta_rec_bf
drivers/net/wireless/mediatek/mt76/mt76_connac_mcu.h: struct sta_rec_bfee
include/linux/platform_data/cyttsp4.h: struct touch_framework
include/linux/platform_data/cyttsp4.h: struct touch_settings
drivers/scsi/wd719x.h: struct wd719x_scb
drivers/scsi/storvsc_drv.c: struct vstor_packet
drivers/net/wwan/iosm/iosm_ipc_mux.h: struct iosm_mux
include/linux/atmdev.h: struct atm_skb_data
drivers/staging/rtl8723bs/include/wlan_bssdef.h: struct wlan_bssid_ex
drivers/infiniband/ulp/iser/iscsi_iser.h: struct iser_login_desc
include/sound/sof/topology.h: struct sof_ipc_comp
drivers/net/wireless/intel/ipw2x00/ipw2200.h: struct clx2_queue
drivers/net/wireless/intel/ipw2x00/ipw2200.h: struct host_cmd
drivers/net/wireless/intel/ipw2x00/ipw2200.h: struct ipw_fw_error
drivers/staging/rtl8192e/rtl819x_HT.h: struct rt_hi_throughput
drivers/net/wireless/marvell/mwifiex/decl.h: struct mwifiex_11h_intf_state
drivers/net/wireless/marvell/mwifiex/decl.h: struct mwifiex_radar_params
security/tomoyo/common.h: struct tomoyo_acl_info
drivers/net/wireless/ti/wl1251/acx.h: struct wl1251_acx_mem_map
drivers/net/wireless/ath/ath10k/core.h: struct ath10k_skb_cb
include/linux/perf_event.h: struct perf_raw_frag
net/nfc/nci/hci.c: struct nci_data
include/net/sctp/ulpevent.h: struct sctp_ulpevent
drivers/net/wireless/ath/ath10k/wmi.h: struct mcast_bcast_rate
drivers/net/wireless/ath/ath10k/wmi.h: struct wmi_bcn_filter_rx_cmd
drivers/net/wireless/ath/ath10k/wmi.h: struct wmi_pno_scan_req
drivers/net/wireless/ath/ath10k/wmi.h: struct wmi_tim_info_arg
sound/soc/qcom/qdsp6/audioreach.c: struct apm_graph_open_params
include/uapi/sound/sof/fw.h: struct snd_sof_blk_hdr
include/uapi/sound/sof/fw.h: struct snd_sof_mod_hdr
drivers/staging/wlan-ng/p80211ioctl.h: struct p80211ioctl_req
drivers/infiniband/ulp/isert/ib_isert.h: struct iser_tx_desc
drivers/infiniband/core/mad_priv.h: struct ib_mad_private
include/linux/hyperv.h: struct vmbus_channel_message_header
drivers/infiniband/hw/irdma/osdep.h: struct irdma_dma_mem
drivers/infiniband/hw/irdma/osdep.h: struct irdma_virt_mem
drivers/crypto/qat/qat_common/adf_cfg_user.h: struct adf_user_cfg_key_val
drivers/net/wireless/marvell/libertas/rx.c: struct rx80211packethdr
include/linux/printk.h: struct pi_entry
net/mac80211/trace.h: struct trace_vif_entry
drivers/staging/r8188eu/include/wlan_bssdef.h: struct wlan_bssid_ex
arch/riscv/include/asm/alternative.h: struct alt_entry
include/uapi/linux/vbox_vmmdev_types.h: struct 
vmmdev_hgcm_function_parameter32
include/uapi/linux/vbox_vmmdev_types.h: struct 
vmmdev_hgcm_function_parameter64
drivers/nfc/st21nfca/st21nfca.h: struct st21nfca_dep_info
drivers/media/test-drivers/vidtv/vidtv_psi.h: struct vidtv_psi_desc
drivers/media/test-drivers/vidtv/vidtv_psi.h: struct 
vidtv_psi_desc_network_name
drivers/media/test-drivers/vidtv/vidtv_psi.h: struct 
vidtv_psi_desc_registration
drivers/media/test-drivers/vidtv/vidtv_psi.h: struct vidtv_psi_desc_service
drivers/media/test-drivers/vidtv/vidtv_psi.h: struct 
vidtv_psi_desc_service_list
drivers/media/test-drivers/vidtv/vidtv_psi.h: struct 
vidtv_psi_desc_service_list_entry
drivers/media/test-drivers/vidtv/vidtv_psi.h: struct 
vidtv_psi_desc_short_event
drivers/media/test-drivers/vidtv/vidtv_psi.h: struct vidtv_psi_table_eit
drivers/media/test-drivers/vidtv/vidtv_psi.h: struct 
vidtv_psi_table_eit_event
drivers/media/test-drivers/vidtv/vidtv_psi.h: struct vidtv_psi_table_nit
drivers/media/test-drivers/vidtv/vidtv_psi.h: struct vidtv_psi_table_pat
drivers/media/test-drivers/vidtv/vidtv_psi.h: struct 
vidtv_psi_table_pat_program
drivers/media/test-drivers/vidtv/vidtv_psi.h: struct vidtv_psi_table_pmt
drivers/media/test-drivers/vidtv/vidtv_psi.h: struct 
vidtv_psi_table_pmt_stream
drivers/media/test-drivers/vidtv/vidtv_psi.h: struct vidtv_psi_table_sdt
drivers/media/test-drivers/vidtv/vidtv_psi.h: struct 
vidtv_psi_table_sdt_service
drivers/media/test-drivers/vidtv/vidtv_psi.h: struct 
vidtv_psi_table_transport
drivers/hv/hv_balloon.c: struct dm_info_header
drivers/input/touchscreen/cyttsp4_core.h: struct cyttsp4_sysinfo_ptr
fs/eventpoll.c: struct epoll_filefd
drivers/net/wireless/ath/ath11k/core.h: struct ath11k_skb_cb
fs/vboxsf/shfl_hostintf.h: struct shfl_createparms
fs/vboxsf/shfl_hostintf.h: struct shfl_fsobjattr
drivers/net/ethernet/mellanox/mlx5/core/esw/vporttbl.c: struct 
mlx5_vport_key
drivers/usb/typec/ucsi/ucsi_ccg.c: struct ucsi_ccg_altmode
drivers/net/wireless/ti/wlcore/wlcore_i.h: struct wl12xx_rx_filter_field
drivers/scsi/qla2xxx/qla_edif_bsg.h: struct extra_auth_els
drivers/scsi/qla2xxx/qla_def.h: struct ql_vnd_mng_host_port_param
drivers/scsi/qla2xxx/qla_def.h: struct ql_vnd_mng_host_stats_param
drivers/staging/rtl8192u/r819xU_phy.h: struct sw_chnl_cmd
drivers/net/wireless/ath/wcn36xx/hal.h: struct wcn36xx_hal_config_bss_params
drivers/net/wireless/ath/wcn36xx/hal.h: struct 
wcn36xx_hal_config_bss_params_v1
drivers/net/wireless/ath/wcn36xx/hal.h: struct wcn36xx_hal_config_sta_params
drivers/net/wireless/ath/wcn36xx/hal.h: struct 
wcn36xx_hal_config_sta_params_v1
drivers/net/wireless/ath/wcn36xx/hal.h: struct 
wcn36xx_hal_finish_scan_req_msg
drivers/net/wireless/ath/wcn36xx/hal.h: struct wcn36xx_hal_join_req_msg
drivers/net/wireless/ath/wcn36xx/hal.h: struct wcn36xx_hal_keys
drivers/net/wireless/ath/wcn36xx/hal.h: struct 
wcn36xx_hal_mac_start_parameters
drivers/net/wireless/ath/wcn36xx/hal.h: struct 
wcn36xx_hal_mac_stop_req_params
drivers/net/wireless/ath/wcn36xx/hal.h: struct 
wcn36xx_hal_remove_bss_key_req_msg
drivers/net/wireless/ath/wcn36xx/hal.h: struct 
wcn36xx_hal_remove_sta_key_req_msg
drivers/net/wireless/ath/wcn36xx/hal.h: struct 
wcn36xx_hal_set_bss_key_req_msg
drivers/net/wireless/ath/wcn36xx/hal.h: struct 
wcn36xx_hal_set_link_state_req_msg
drivers/net/wireless/ath/wcn36xx/hal.h: struct 
wcn36xx_hal_set_sta_key_params
drivers/net/wireless/ath/wcn36xx/hal.h: struct 
wcn36xx_hal_start_scan_offload_req_msg
drivers/net/wireless/ath/wcn36xx/hal.h: struct wcn36xx_hal_supported_rates
drivers/net/wireless/ath/wcn36xx/hal.h: struct 
wcn36xx_hal_supported_rates_v1
drivers/net/wireless/ath/wcn36xx/hal.h: struct 
wcn36xx_hal_switch_channel_req_msg
drivers/net/wireless/ath/wcn36xx/hal.h: struct 
wcn36xx_hal_update_scan_params_req
drivers/net/wireless/ath/wcn36xx/hal.h: struct 
wcn36xx_hal_update_scan_params_req_ex
drivers/net/wireless/ath/ath11k/wmi.h: struct wmi_request_stats_cmd
drivers/net/wireless/ath/ath11k/wmi.h: struct wmi_vdev_start_resp_event
drivers/net/wireless/intel/ipw2x00/ipw2100.h: struct ipw2100_cmd_header
sound/soc/intel/atom/sst-mfld-dsp.h: struct snd_sst_runtime_params
drivers/misc/mei/hdcp/mei_hdcp.h: struct hdcp_cmd_header
arch/s390/include/asm/debug.h: struct __debug_entry

Keisuke

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Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

[Russell King (Oracle)]

On Mon, May 30, 2022 at 03:35:28PM +0200, Arnd Bergmann wrote:
> The annotations for edid are completely correct and necessary. However
> other driver authors just slap __packed annotations on any structure
> even if the layout is not fixed at all like:
> 
> struct my_driver_priv {
>        struct device dev;
>        u8 causes_misalignment;
>        spinlock_t lock;
>        atomic_t counter;
> } __packed; /* this annotation is harmful because it breaks the atomics */
> 
> or if the annotation does not change the layout like
> 
> struct my_dma_descriptor {
>      __le64 address;
>      __le64 length;
> } __packed; /* does not change layout but makes access slow on some
> architectures */

Sounds like we need a howto document for people to ignore and continue
doing their own thing. :P

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Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

[Russell King (Oracle)]

On Mon, May 30, 2022 at 02:43:45PM +0200, Arnd Bergmann wrote:
> Overall I'm not that worried because the only machines running OABI
> kernels would be on really old hardware that runs a limited set of
> driver code.

... and from what I remember, none of them care about EDID anyway.

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Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

[Russell King (Oracle)]

On Mon, May 30, 2022 at 12:33:17PM +0300, Jani Nikula wrote:
> On Mon, 30 May 2022, Jani Nikula <jani.nikula@intel.com> wrote:
> > On Sat, 28 May 2022, Linus Torvalds <torvalds@linux-foundation.org> wrote:
> >> On Sat, May 28, 2022 at 11:59 AM Arnd Bergmann <arnd@arndb.de> wrote:
> >>>
> >>> It's CONFIG_ARM_AEABI, which is normally set everywhere. Without this
> >>> option, you the kernel is built for the old 'OABI' that forces all non-packed
> >>> struct members to be at least 16-bit aligned.
> >>
> >> Looks like forced word (32 bit) alignment to me.
> >>
> >> I wonder how many other structures that messes up, but I committed the
> >> EDID fix for now.
> >
> > Thanks for the fix, and the thorough commit message!
> >
> >> This has presumably been broken for a long time, but maybe the
> >> affected targets don't typically use EDID and kernel modesetting, and
> >> only use some fixed display setup instead.
> >>
> >> Those structure definitions go back a _loong_ time (from a quick 'git
> >> blame' I see November 2008).
> >>
> >> But despite that, I did not mark my fix 'cc:stable' because I don't
> >> know if any of those machines affected by this bad arm ABI issue could
> >> possibly care.
> >>
> >> At least my tree hopefully now builds on them, with the BUILD_BUG_ON()
> >> that uncovered this.
> >
> > Indeed the bug is ancient. I just threw in the BUILD_BUG_ON() on a whim
> > as an extra sanity check when doing pointer arithmetics on struct edid
> > *.
> >
> > If there are affected machines, buffer overflows are the real danger due
> > to edid->extensions indicating the number of extensions.
> 
> That is, for EDID. Makes you wonder about all the other packed structs
> with enum members across the kernel.

enum should not be used in structures if the layout of the struct
matters. ISTR there was a proposal for EABI to make enums just about
big enough to hold their enumerated constants - so you'd end up with
8-bit, 16-bit etc according to the largest enumerated value that the
compiler thinks it could hold.

That's a latent disaster when enums get used in structs where the
layout matters, __packed or not.

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Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

[Russell King (Oracle)]

On Sat, May 28, 2022 at 11:08:48AM -0700, Linus Torvalds wrote:
> This smells like a compiler bug triggered by "there's a 16-bit member
> field in that gtf2 structure, and despite it being packed and aligned
> to 1, we somehow still align the size to 2".

It's an age old thing, it's no compiler bug, and it's completely
compliant with the C standards. Implementations are permitted by the
C standard to pad structures and unions how they see fit - and some
do if it makes sense for performance.

The mistake is that people forget this detail, and they expect
structs and unions to be laid out a certain way - because it doesn't
matter to the same extent on x86.

However, as older ARM CPUs could not do unaligned loads, ensuring
that things were naturally aligned made complete sense, even if it
meant that people who assume the world is x86 got tripped up - the
only way around that would be to make every load very expensive.

It's not "align to size of 2" in OABI, it tends to be align to a
multiple of 4, because the underlying architecture is 32-bit.

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