linux-kernel - Re: OT: calling kernel syscall manually

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Message-ID: <787b0d920609122235j57ac327ckcc8d08832fb3989c@mail.gmail.com>
Date:	Wed, 13 Sep 2006 01:35:08 -0400
From:	"Albert Cahalan" <acahalan@...il.com>
To:	dwmw2@...radead.org, guest01@...il.com,
	linux-kernel@...r.kernel.org
Subject: Re: OT: calling kernel syscall manually

David Woodhouse writes:
> On Tue, 2006-09-12 at 14:05 +0200, guest01 wrote:

>> 3 -> using kernel directly
>>
>> Ok, the third one is a little bit tricky, at least for me.
>> I found an example for lseek, but I don't know how to convert
>> that for mkdir. I don't know the necessary arguments, ..
>
> The third one has always been broken on i386 for PIC code

No, I was just using it today in PIC i386 code.
The %ebx register gets pushed, the needed value
gets moved into %ebx, the int 0x80 is done, and
the %ebx register gets popped. Only a few odd
calls like clone() need something different.

(not that this should be needed: gcc is broken
if it can't save/restore the needed registers)

> and was pointless anyway, since glibc provides this
> functionality. The kernel method has been removed from
> userspace visibility all architectures, and we plan to
> remove it entirely in 2.6.19 since it's not at all useful.

It's damn useful. Hint: Linux does not require glibc.

I could hack up my own assembly. I did that for clone(),
but I didn't enjoy that waste of my time.
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