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 20:39:41 +0800
From:	"Zhangjian (Bamvor)" <bamvor.zhangjian@...wei.com>
To:	Arnd Bergmann <arnd@...db.de>,
	<linux-arm-kernel@...ts.infradead.org>
CC:	<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>,
	"Zhangjian (Bamvor)" <bamvor.zhangjian@...wei.com>
Subject: Re: [PATCH 20/25] arm64:ilp32: add sys_ilp32.c and a separate table
 (in entry.S) to use it

Hi,

On 2016/5/10 19:48, Arnd Bergmann wrote:
> 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.
Yes, I think so. I am puzzle that how do we ensure that all the new
32bit architecture will define off_t as 64bit after introduce
ARCH_32BIT_OFF_T and do not change any other code?
>
>>       @@ -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.
Yes. But if we do not change __kernel_long_t and __kernel_ulong_t, the
application of ilp32 will think size of long in kernel is 32bit. Is that
correct?
>
>>
>> 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.
Ok, I will test the ltp syscall test.
With this changes, the issue I mentioned should be fixed. But we still
use mmap2 syscall for ILP32 application when we pass the offset instead
of page offset. Is it correct?

Regards

Bamvor

>
> 	Arnd
>