[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID: <CAJ86T=XGHYkCba20Dy5yFeRMWaTWtM8BJtJnSP6mExYDfkbfYA@mail.gmail.com>
Date: Fri, 15 Mar 2019 01:32:48 -0700
From: Andre McCurdy <armccurdy@...il.com>
To: musl@...ts.openwall.com
Subject: Re: do we need different definition of __SYSCALL_LL_E for
different endian?
On Thu, Mar 14, 2019 at 9:15 PM wangjianjian (C)
<wangjianjian3@...wei.com> wrote:
>
> This is arm definition of macro __SYSCALL_LL_E:
> #define __SYSCALL_LL_E(x) \
> 2 ((union { long long ll; long l[2]; }){ .ll = x }).l[0], \
> 3 ((union { long long ll; long l[2]; }){ .ll = x }).l[1]
>
> But do we need to deferent definitions for different endian?
> From Linux man page,
>
> For example, on the ARM architecture Embedded ABI (EABI), a 64-bit value (e.g., long long) must be aligned to an even register pair. Thus, using
> syscall() instead of the wrapper provided by glibc, the readahead() system call would be invoked as follows on the ARM architecture with the EABI:
>
> syscall(SYS_readahead, fd, 0,
> (unsigned int) (offset >> 32),
> (unsigned int) (offset & 0xFFFFFFFF),
> count);
You seem to be looking at an out of date version of the man page.
Later versions have been fixed to make it clearer that the order is
endian specific:
http://man7.org/linux/man-pages/man2/syscall.2.html
> Seems the third argument is the high 32 bit and the fourth argument is the low 32 bit. So do we need below fix?
> #ifdef __ARM_BIG_ENDIAN
> #define __SYSCALL_LL_E(x) \
> 2 ((union { long long ll; long l[2]; }){ .ll = x }).l[0], \
> 3 ((union { long long ll; long l[2]; }){ .ll = x }).l[1]
> #else
> #define __SYSCALL_LL_E(x) \
> 2 ((union { long long ll; long l[2]; }){ .ll = x }).l[1], \
> 3 ((union { long long ll; long l[2]; }){ .ll = x }).l[0]
> #endif
>
> Thanks.
>
> BR,
> Wang Jianjian
>
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
