Re: [PATCH 06/10] staging/android: turn fence_info into a __64 pointer

[Gustavo Padovan]

2016-02-01 Gustavo Padovan :

> Hi Maarten,
> 
> 2016-02-01 Maarten Lankhorst :
> 
> > Op 29-01-16 om 22:20 schreef Gustavo Padovan:
> > > From: Gustavo Padovan 
> > >
> > > Making fence_info a pointer enables us to extend the struct in the future
> > > without breaking the ABI.
> > >
> > > Signed-off-by: Gustavo Padovan 
> > > ---
> > >  drivers/staging/android/sync.c  | 2 +-
> > >  drivers/staging/android/uapi/sync.h | 2 +-
> > >  2 files changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/staging/android/sync.c 
> > > b/drivers/staging/android/sync.c
> > > index f7530f0..51d4f47 100644
> > > --- a/drivers/staging/android/sync.c
> > > +++ b/drivers/staging/android/sync.c
> > > @@ -525,7 +525,7 @@ static long sync_file_ioctl_fence_info(struct 
> > > sync_file *sync_file,
> > >   if (info->status >= 0)
> > >   info->status = !info->status;
> > >  
> > > - len = sizeof(struct sync_file_info);
> > > + len = sizeof(struct sync_file_info) - sizeof(__u64 *);
> > >  
> > >   for (i = 0; i < sync_file->num_fences; ++i) {
> > >   struct fence *fence = sync_file->cbs[i].fence;
> > > diff --git a/drivers/staging/android/uapi/sync.h 
> > > b/drivers/staging/android/uapi/sync.h
> > > index ed281fc..9f07aa7 100644
> > > --- a/drivers/staging/android/uapi/sync.h
> > > +++ b/drivers/staging/android/uapi/sync.h
> > > @@ -54,7 +54,7 @@ struct sync_file_info {
> > >   charname[32];
> > >   __s32   status;
> > >  
> > > - __u8fence_info[0];
> > > + __u64   *fence_info;
> > >  };
> > >
> > Pointers are awful, it should be a __u64 since it's a pointer type. 
> > Userspace should cast it to a uintptr_t in userspace.
> 
> Oh, I made a mistake. I'll fix this.
> 
> 
> > This structure also won't work on 64-bits systems, there may be a hole 
> > between fence_info and status (or num_fences in next patch).
> > 
> > It's probably best to move it to the top and ensure the struct is 64-bits 
> > aligned.
> 
> That is not possible because we are not allocating only 64bits there but
> a array of struct fence_info, so it needs to be the last one. Maybe we
> can add some sort of padding?

Actually it is 64bits aligned:

struct sync_file_info { 
charname[32];   
__s32   status; 
__u32   flags;  
__u32   num_fences; 
__u32   len;

__u64   fence_info; 
};

So nothing to worry here.

Gustavo
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Re: [PATCH 06/10] staging/android: turn fence_info into a __64 pointer

[Maarten Lankhorst]

Op 29-01-16 om 22:20 schreef Gustavo Padovan:
> From: Gustavo Padovan 
>
> Making fence_info a pointer enables us to extend the struct in the future
> without breaking the ABI.
>
> Signed-off-by: Gustavo Padovan 
> ---
>  drivers/staging/android/sync.c  | 2 +-
>  drivers/staging/android/uapi/sync.h | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c
> index f7530f0..51d4f47 100644
> --- a/drivers/staging/android/sync.c
> +++ b/drivers/staging/android/sync.c
> @@ -525,7 +525,7 @@ static long sync_file_ioctl_fence_info(struct sync_file 
> *sync_file,
>   if (info->status >= 0)
>   info->status = !info->status;
>  
> - len = sizeof(struct sync_file_info);
> + len = sizeof(struct sync_file_info) - sizeof(__u64 *);
>  
>   for (i = 0; i < sync_file->num_fences; ++i) {
>   struct fence *fence = sync_file->cbs[i].fence;
> diff --git a/drivers/staging/android/uapi/sync.h 
> b/drivers/staging/android/uapi/sync.h
> index ed281fc..9f07aa7 100644
> --- a/drivers/staging/android/uapi/sync.h
> +++ b/drivers/staging/android/uapi/sync.h
> @@ -54,7 +54,7 @@ struct sync_file_info {
>   charname[32];
>   __s32   status;
>  
> - __u8fence_info[0];
> + __u64   *fence_info;
>  };
>
Pointers are awful, it should be a __u64 since it's a pointer type. Userspace 
should cast it to a uintptr_t in userspace.
This structure also won't work on 64-bits systems, there may be a hole between 
fence_info and status (or num_fences in next patch).

It's probably best to move it to the top and ensure the struct is 64-bits 
aligned.
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Re: [PATCH 06/10] staging/android: turn fence_info into a __64 pointer

[Gustavo Padovan]

Hi Maarten,

2016-02-01 Maarten Lankhorst :

> Op 29-01-16 om 22:20 schreef Gustavo Padovan:
> > From: Gustavo Padovan 
> >
> > Making fence_info a pointer enables us to extend the struct in the future
> > without breaking the ABI.
> >
> > Signed-off-by: Gustavo Padovan 
> > ---
> >  drivers/staging/android/sync.c  | 2 +-
> >  drivers/staging/android/uapi/sync.h | 2 +-
> >  2 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c
> > index f7530f0..51d4f47 100644
> > --- a/drivers/staging/android/sync.c
> > +++ b/drivers/staging/android/sync.c
> > @@ -525,7 +525,7 @@ static long sync_file_ioctl_fence_info(struct sync_file 
> > *sync_file,
> > if (info->status >= 0)
> > info->status = !info->status;
> >  
> > -   len = sizeof(struct sync_file_info);
> > +   len = sizeof(struct sync_file_info) - sizeof(__u64 *);
> >  
> > for (i = 0; i < sync_file->num_fences; ++i) {
> > struct fence *fence = sync_file->cbs[i].fence;
> > diff --git a/drivers/staging/android/uapi/sync.h 
> > b/drivers/staging/android/uapi/sync.h
> > index ed281fc..9f07aa7 100644
> > --- a/drivers/staging/android/uapi/sync.h
> > +++ b/drivers/staging/android/uapi/sync.h
> > @@ -54,7 +54,7 @@ struct sync_file_info {
> > charname[32];
> > __s32   status;
> >  
> > -   __u8fence_info[0];
> > +   __u64   *fence_info;
> >  };
> >
> Pointers are awful, it should be a __u64 since it's a pointer type. Userspace 
> should cast it to a uintptr_t in userspace.

Oh, I made a mistake. I'll fix this.


> This structure also won't work on 64-bits systems, there may be a hole 
> between fence_info and status (or num_fences in next patch).
> 
> It's probably best to move it to the top and ensure the struct is 64-bits 
> aligned.

That is not possible because we are not allocating only 64bits there but
a array of struct fence_info, so it needs to be the last one. Maybe we
can add some sort of padding?


Gustavo
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Re: [PATCH 06/10] staging/android: turn fence_info into a __64 pointer

[Emil Velikov]

Hi Gustavo,

s/__64/__u64/ in the commit message.

On 29 January 2016 at 23:20, Gustavo Padovan  wrote:
> From: Gustavo Padovan 
>
> Making fence_info a pointer enables us to extend the struct in the future
> without breaking the ABI.
>
> Signed-off-by: Gustavo Padovan 

> diff --git a/drivers/staging/android/uapi/sync.h 
> b/drivers/staging/android/uapi/sync.h
> index ed281fc..9f07aa7 100644
> --- a/drivers/staging/android/uapi/sync.h
> +++ b/drivers/staging/android/uapi/sync.h
> @@ -54,7 +54,7 @@ struct sync_file_info {
> charname[32];
> __s32   status;
>
> -   __u8fence_info[0];
> +   __u64   *fence_info;
I believe you misinterpreted what was meant with "_u64 pointer". As
the storage use for of a pointer varies across 32/64 bit arch, we
explicitly use a variable type that is large enough (and consistent)
for both cases. Thus the above should be

+   __u64   fence_info;

Hope this clarifies things.

-Emil
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[PATCH 06/10] staging/android: turn fence_info into a __64 pointer

[Gustavo Padovan]

From: Gustavo Padovan 

Making fence_info a pointer enables us to extend the struct in the future
without breaking the ABI.

Signed-off-by: Gustavo Padovan 
---
 drivers/staging/android/sync.c  | 2 +-
 drivers/staging/android/uapi/sync.h | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c
index f7530f0..51d4f47 100644
--- a/drivers/staging/android/sync.c
+++ b/drivers/staging/android/sync.c
@@ -525,7 +525,7 @@ static long sync_file_ioctl_fence_info(struct sync_file 
*sync_file,
if (info->status >= 0)
info->status = !info->status;
 
-   len = sizeof(struct sync_file_info);
+   len = sizeof(struct sync_file_info) - sizeof(__u64 *);
 
for (i = 0; i < sync_file->num_fences; ++i) {
struct fence *fence = sync_file->cbs[i].fence;
diff --git a/drivers/staging/android/uapi/sync.h 
b/drivers/staging/android/uapi/sync.h
index ed281fc..9f07aa7 100644
--- a/drivers/staging/android/uapi/sync.h
+++ b/drivers/staging/android/uapi/sync.h
@@ -54,7 +54,7 @@ struct sync_file_info {
charname[32];
__s32   status;
 
-   __u8fence_info[0];
+   __u64   *fence_info;
 };
 
 #define SYNC_IOC_MAGIC '>'
-- 
2.5.0

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