linux-kernel - Re: [PATCH 20/25] arm64:ilp32: add sys_ilp32.c and a separate table (in entry.S) to use it

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Date:	Tue, 10 May 2016 13:48:06 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	"Zhangjian (Bamvor)" <bamvor.zhangjian@...wei.com>,
	linux-doc@...r.kernel.org,
	Andrew Pinski <Andrew.Pinski@...iumnetworks.com>,
	catalin.marinas@....com, heiko.carstens@...ibm.com,
	Yury Norov <ynorov@...iumnetworks.com>,
	Hanjun Guo <guohanjun@...wei.com>, joseph@...esourcery.com,
	linux-arch@...r.kernel.org, linux-s390@...r.kernel.org,
	"jijun (D)" <jijun2@...wei.com>, Prasun.Kapoor@...iumnetworks.com,
	schwab@...e.de, agraf@...e.de, pinskia@...il.com,
	klimov.linux@...il.com, broonie@...nel.org,
	Nathan_Lynch@...tor.com, linux-kernel@...r.kernel.org,
	Andrew Pinski <apinski@...ium.com>, schwidefsky@...ibm.com,
	christoph.muellner@...obroma-systems.com
Subject: Re: [PATCH 20/25] arm64:ilp32: add sys_ilp32.c and a separate table (in entry.S) to use it

On Tuesday 10 May 2016 17:47:26 Zhangjian wrote:
> On 2016/5/10 16:36, Arnd Bergmann wrote:
> > On Tuesday 10 May 2016 15:42:07 Zhangjian wrote:
> >> On 2016/5/6 20:37, Yury Norov wrote:
> 
> "include/uapi/asm-generic/posix_types.h" is uapi, we could not check
> "ARCH_32BIT_OFF_T" here. Besides, the `__kernel_long_t` is long which
> mean it is 32bit in ILP32. should we define something like x32?
>      ```
>      diff --git a/arch/arm64/include/uapi/asm/posix_types.h b/arch/arm64/include/uapi/asm/posix_types.h
>      index 7985ff6..9baa8d3 100644
>      --- a/arch/arm64/include/uapi/asm/posix_types.h
>      +++ b/arch/arm64/include/uapi/asm/posix_types.h

glibc does not use the definition of __kernel_off_t, it has its own
copy, so changing the kernel headers would do nothing.

>      @@ -5,6 +5,9 @@ typedef unsigned short __kernel_old_uid_t;
>       typedef unsigned short __kernel_old_gid_t;
>        #define __kernel_old_uid_t __kernel_old_uid_t
> 
>       +typedef long long __kernel_long_t;
>       +typedef unsigned long long __kernel_ulong_t;
>       +
>        #include <asm-generic/posix_types.h>
> 
>        #endif /*  __ASM_POSIX_TYPES_H */u
>      ```

This would break all sorts of things, because __kernel_long_t/__kernel_ulong_t
are not just used for off_t but also other things.

> 
> On the other hand, glibc define it own off_t in "bits/types.h":
>      __STD_TYPE __OFF_T_TYPE __off_t;        /* Type of file sizes and offsets.  */
>      __STD_TYPE __OFF64_T_TYPE __off64_t;    /* Type of file sizes and offsets (LFS).  */
> 
> in "sysdeps/unix/sysv/linux/aarch64/bits/typesizes.h":
>      #define __OFF_T_TYPE            __SLONGWORD_TYPE
>      #define __OFF64_T_TYPE          __SQUAD_TYPE
> 
> If we define off_t as 64bit in glibc:
>      #define __OFF_T_TYPE           __SQUAD_TYPE
> 
> Should We need to align all the off_t syscall to 64bit syscall in
> kernel?
> 

Yes, this is the change that I think we need to make, along with
the same change for __INO_T_TYPE and 

#define __OFF_T_MATCHES_OFF64_T        1
#define __INO_T_MATCHES_INO64_T        1

If I read the rest of the glibc headers right, that should be all we need
to ensure that both off_t and off64_t match the __kernel_loff_t based
syscalls.

	Arnd