Re: [COMMITTED PATCH] Move tilegx, tilepro, and linux-generic from ports to libc.

[Szabolcs Nagy <szabolcs dot nagy at arm dot com>]

On 19/03/15 16:59, Chris Metcalf wrote:
> On 03/19/2015 12:44 PM, H.J. Lu wrote:
>> On Thu, Mar 19, 2015 at 9:31 AM, Chris Metcalf <cmetcalf@ezchip.com> wrote:
>>> On 03/18/2015 07:59 AM, H.J. Lu wrote:
>>>> Any particular reason to add sysdeps/unix/sysv/linux/generic/bits/statfs.h
>>>> when there is sysdeps/unix/sysv/linux/bits/statfs.h already? Why can't it be
>>>> used?
>>>
>>> The distinction lies with the the fields defined by __field64 in the
>>> "generic" version.  For the case without __USE_FILE_OFFSET64, but when ILP32
>>> mode is involved, the base linux version uses plain __fsblkcnt_t, i.e.
>>> unsigned long, so just 32 bits.  However, it needs to be a 64-bit field,
>>> where either the first or second 32-bit subfield is padding depending on
>>> endianness, and the field value is the other 32-bit subfield.  We would need
>>> to adopt the __field64 scheme for the base version in some way that allowed
>>> platforms to turn it on as needed (depending on whether statfs is filled
>>> with a statfs64 syscall or a plain 32-bit statfs syscall on older, non
>>> asm-generic 32-bit kernels).  This is doable but fiddly to get exactly
>>> right.
>>>
>>> Another difference I see is easy to work around.  The "generic" linux
>>> version uses __SWORD_TYPE where the base version uses __fsword_t (changed by
>>> hjl in 2012).  If the generic platforms (tile, aarch64, nios2) switched,
>>> this would be OK since the types are the same on those platforms.  (Only
>>> alpha and x32 define them differently.)
>> There are
>>
>> sysdeps/unix/sysv/linux/mips/bits/statfs.h
>> sysdeps/unix/sysv/linux/alpha/bits/statfs.h
>> sysdeps/unix/sysv/linux/bits/statfs.h
>> sysdeps/unix/sysv/linux/s390/bits/statfs.h
>>
>> If sysdeps/unix/sysv/linux/bits/statfs.h can't be used for
>> a Linux platform, it should define its own statfs.h, like
>> alpha, mips and s390.
> 
> The linux/generic layer is essentially an intermediate  layer for all 
> new Linux ports that use the asm-generic syscall interface. Rather than 
> "inheriting" directly from the sysdeps/unix/sysv/linux/, newer ports 
> inherit from sysdeps/unix/sysv/linux/generic/, which tweaks whatever 
> needs tweaking to support the fact that a far smaller set of syscalls is 
> available on such platforms.  This means tile, aarch64, and nios2 don't 
> have to each provide their own replacement statfs.h.
> 

i think aarch64 does not want 32bit blkcnt, that breaks on
a large fs (not even with ilp32)

i'm surprised it is in use on newer 32bit archs at all
(if it is then i think linux asm-generic needs a fix)

>> Having both
>>
>> sysdeps/unix/sysv/linux/generic/bits/statfs.h
>>
>> and
>>
>> sysdeps/unix/sysv/linux/bits/statfs.h
>>
>> is very strange.
> 
> Yes, I don't love the naming either, but no one could come up with 
> anything better when this was initially introduced.
> 
> It may be the case that we can do some unification along the lines I 
> suggested in my previous email, but the tricky part is figuring out 
> programmatically which platforms are using the new API (and thus don't 
> have a version of statfs with 32-bit fsword_t) and which are using the 
> old API.  Or, moving forward, which platforms are using the LP64 version 
> of the syscall even in ILP32 mode (x32, aarch64:ILP32).  Since this is a 
> public header we don't have kernel-features.h.  I'm not sure where else 
> we would normally place this kind of information in the headers.
>