From: Jeff Garzik <jeff@garzik.org>
To: LKML <linux-kernel@vger.kernel.org>
Cc: x86@kernel.org
Subject: [x86] Strange 64-bit put_user ?
Date: Tue, 28 Apr 2009 13:32:06 -0400 [thread overview]
Message-ID: <49F73D96.2090801@garzik.org> (raw)
In arch/x86/include/asm/uaccess.h, if !CONFIG_X86_32, we see
> #define __put_user_x8(x, ptr, __ret_pu) \
> ({ u64 __ret_pu; __put_user_x(8, x, ptr, __ret_pu); (int)__ret_pu; })
which was preceded by
> #define __put_user_x(size, x, ptr, __ret_pu) \
> asm volatile("call __put_user_" #size : "=a" (__ret_pu) \
> :"0" ((typeof(*(ptr)))(x)), "c" (ptr) : "ebx")
My question, from an admitted inline asm newbie:
Why is 32-bit register 'ebx' being used for a 64-bit put_user?
And a dumb-question follow-up, probably easy, for any x86 expert: why
are registers 'bl' and 'bx' not used for 8-bit and 16-bit put_user,
respectively?
Thanks,
Jeff
next reply other threads:[~2009-04-28 17:32 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-04-28 17:32 Jeff Garzik [this message]
2009-04-29 0:31 ` [x86] Strange 64-bit put_user ? H. Peter Anvin
2009-04-29 20:00 ` Jeff Garzik
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