Date: Mon, 08 Sep 2014 11:44:27 -0400 From: John Baldwin <jhb@freebsd.org> To: freebsd-doc@freebsd.org Subject: Re: Syscall x86 convention in Devlopers' Handbook Message-ID: <1928479.9KfryLvuNc@ralph.baldwin.cx> In-Reply-To: <396A5D5F-AED3-4D79-8CD4-356A7FECCF9F@icloud.com> References: <396A5D5F-AED3-4D79-8CD4-356A7FECCF9F@icloud.com>
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On Saturday, September 06, 2014 02:40:33 PM Seo Townsend wrote: > Hey guys, this is my first time in this mailing list so I’m not fully aware > of all the procedures… > > I was looking through the developer handbook and noticed that the > Developer’s Handbook section on Assembly for x86 doesn’t make any mention > of the change in the syscall calling convention from i386 to x86-64 and I > can’t seem to find this documented anywhere. The documentation does > mention “FreeBSD kernel uses the C calling convention” (11.3.1) but doesn’t > point out that the C calling convention changed from i386 to x86-64; and > the architecture listed for 11 is generically (x86 Assembly Language > Programming). Arguably, the "C calling convention" on x86-64 is to pass by register since that is what C uses on x86-64, so I'm not sure the statement is wrong. > Thoughts? Some ideas I had are: > (1). Change “x86 Assembly Language Programming” to “i386 Assembly” - This > would clear up the disambiguity of the 32bit architecture and 64bit > architecture. I think this is probably a fine thing to do. > (2). Add a footnote to (11.3.1) with “If you are using > x86-64, please note that the calling convention for both C and syscall > changed from pushing arguments on the stack to using a list of ordered > registered as outlined in the System V AMD64 ABI specification” I don't really think this is the proper place to document the well-known x86-64 calling conventions. :) If you are programming 64-bit assembly you should already know those. > (3). I would not mind eventually adding a section for “x86-64 assembly” for > (11.3.2) if I could get someone to help mentor me. I suspect it would be more useful to just replace the current 32-bit example with only a 64-bit example and not try to keep both. -- John Baldwinhelp
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