From owner-freebsd-hackers@FreeBSD.ORG  Wed Aug 17 15:44:16 2005
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Date: Wed, 17 Aug 2005 21:14:15 +0530
From: Joseph Koshy <joseph.koshy@gmail.com>
To: Dan Nelson <dnelson@allantgroup.com>
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References: <20050817122049.29529.qmail@web52009.mail.yahoo.com>
	<20050817145510.GD26422@dan.emsphone.com>
Cc: hackers@freebsd.org
Subject: Re: hello world but not in 32bit x86 but in amd64 for amd64 platform
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av> "Hello World" assembly program written in 64bit assembly
av> which I can compile and run on my FreeBSD,AMD64 platform

You could also look at "src/lib/libc/amd64/SYS.h" for how
system calls are implemented.  In particular,

  #define KERNCALL        movq %rcx, %r10; syscall

A system call transfers control to:=20

  "src/sys/amd46/amd64/exception.S":
  ... snip ...
  IDTVEC(fast_syscall)
          swapgs
          movq    %rsp,PCPU(SCRATCH_RSP)
          movq    PCPU(RSP0),%rsp
          ... etc ...

The x86-64 ABI is defined in:

   http://x86-64.org/documentation/abi.pdf

--=20
FreeBSD Volunteer,     http://people.freebsd.org/~jkoshy