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Hi, Dave,</div>
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<div style="LINE-HEIGHT: 15pt">Thank you for the kind explanation and I think it will help much for me.</div>
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<div style="LINE-HEIGHT: 15pt">I searched down the uClib as you told me and could locate the kernel sys_write function.</div>
<div style="LINE-HEIGHT: 15pt">In my case, the arch is sparc, and it is defined in fs/read_write.c as you said(in linux kernel source).</div>
<div style="LINE-HEIGHT: 15pt"> </div>
<div style="LINE-HEIGHT: 15pt">I've checked that</div>
<div style="LINE-HEIGHT: 15pt">SYSCALL_DEFINE3(write, unsigned int, fd, const char __user *, buf, size_t, count)</div>
<div style="LINE-HEIGHT: 15pt">is expanded to</div>
<div style="LINE-HEIGHT: 15pt">=> asmlinkage long sys_write(unsigned int fd, const char __user * buf, size_t count)</div>
<div style="LINE-HEIGHT: 15pt"> </div>
<div style="LINE-HEIGHT: 15pt">and I was able to use prom_printf (write to uart) to print what I tried to print in busybox with printf.</div>
<div style="LINE-HEIGHT: 15pt">Now I can see busybox printf at least through the uart port though it's not yet shown on the LCD(which I'm trying to map to tty1 and the shell).</div>
<div style="LINE-HEIGHT: 15pt">Thank you!</div>
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<div style="LINE-HEIGHT: 15pt">Chan</div>
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<div style="LINE-HEIGHT: 15pt"><b>From : </b>"Dave Hylands" <dhylands@gmail.com><br>
<b>Sent : </b>2014-03-13 02:54:40 ( +09:00 )<br>
<b>To : </b>Kim Chan <ckim@etri.re.kr><br>
<b>Cc : </b>Mohan L <l.mohanphy@gmail.com>, kernelnewbies@kernelnewbies.org <kernelnewbies@kernelnewbies.org><br>
<b>Subject : </b>Re: where is the printf source for busybox?<br>
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<div style="LINE-HEIGHT: 15pt" dir="ltr">Hi,<br>
<div class="gmail_extra"><br>
<br>
<div class="gmail_quote">On Tue, Mar 11, 2014 at 11:55 PM, Kim Chan <span dir="ltr">
<<a href="mailto:ckim@etri.re.kr" target="_blank">ckim@etri.re.kr</a>></span> wrote:<br>
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Wow, that was it. I'm happy to hear that because I thought it should end up with a system call anyway.
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<div style="LINE-HEIGHT: 15pt">Then isn't there some codes making the system call? Or is it that the compiler understands that 'write' is a system call and inserts the assembly code for calling it by itself?</div>
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<div>In uclibc, the write source code is found here:<br>
<a href="http://git.uclibc.org/uClibc/tree/libc/sysdeps/linux/common/write.c" target="_blank">http://git.uclibc.org/uClibc/tree/libc/sysdeps/linux/common/write.c</a><br>
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<div>How the syscall is actually implemented is architecture specific, and will be in one of the directories here:<br>
<a href="http://git.uclibc.org/uClibc/tree/libc/sysdeps/linux" target="_blank">http://git.uclibc.org/uClibc/tree/libc/sysdeps/linux</a><br>
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<div>For example, for ARM, with EABI, then I believe that it winds up here:<br>
<a href="http://git.uclibc.org/uClibc/tree/libc/sysdeps/linux/arm/syscall-eabi.S" target="_blank">http://git.uclibc.org/uClibc/tree/libc/sysdeps/linux/arm/syscall-eabi.S</a><br>
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<div>The SWI instruction transfers control to the kernel.<br>
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<div>On the kernel side, how the syscalls get handled is also architecture specific, but it will generally wind up at a function called sys_FUNCTION, however the generation of the function name is usually hidden behind a macro.<br>
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<div>So sys_write in the kernel winds up being declared here:<br>
<a href="http://lxr.linux.no/#linux+v3.13.5/fs/read_write.c#L514" target="_blank">http://lxr.linux.no/#linux+v3.13.5/fs/read_write.c#L514</a><br>
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-- <br>
Dave Hylands<br>
Shuswap, BC, Canada<br>
<a href="http://www.davehylands.com/" target="_blank">http://www.davehylands.com</a>
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