Re: [Xen-devel] [PATCH v2 for-4.7 5/6] xen/xsplice: add ELFOSABI_FREEBSD as a supported OSABI for payloads

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

On Tue, May 03, 2016 at 08:17:15AM -0600, Jan Beulich wrote:
> >>> On 03.05.16 at 12:55, <roger.pau@xxxxxxxxxx> wrote:
> > The calling convention used by the FreeBSD ELF OSABI is exactly the same as
> > the the one defined by System V, so payloads with a FreeBSD OSABI should be
> > accepted by the xsplice machinery.
> 
> Well, you realize that the ABI is more than just the calling convention?
> I.e. your patch basically says ELFOSABI_NONE == ELFOSABI_FREEBSD,
> in which case I wonder why the latter exists in the first place. Is there
> a proper document somewhere describing everything the latter implies,
> so that one can check whether for xSplice purposes such similar
> treatment is indeed okay? Until then I'm afraid I'm opposed to this going
> in.

The FreeBSD elf OSABI only has a meaning for userspace applications, it's 
used by FreeBSD in order to detect if an application is native or if it 
needs to be run in the linuxator (the Linux emulator, or any other emulator 
that is available and matches the ELF OSABI specified in the binary FWIW).

THe only difference from SYSV to FreeBSD OSABI is the sysentvec that's 
selected inside of the FreeBSD kernel (the ABI between the kernel and the 
user-space application), but of course this doesn't apply to kernel code, 
which is what Xen and the xsplice payloads are. Sadly this is not written 
anywhere.

Roger.

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