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

On Wed, May 04, 2016 at 04:34:26AM -0600, Jan Beulich wrote:
> >>> On 04.05.16 at 11:48, <roger.pau@xxxxxxxxxx> wrote:
> > 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.
> Well, okay, in that case I agree the patch should be fine.

Would you like me to resend this with a more expanded commit message, or are 
you going to squash my explanation in the commit message?

Thanks, Roger.

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