Re: [Xen-devel] [PATCH] tools/tests/x86_emulate: #define unlikely in x86 emulator test harness

[Ian Jackson <ian.jackson@xxxxxxxxxxxxx>]

Andrew Cooper writes ("Re: [PATCH] tools/tests/x86_emulate: #define unlikely in 
x86 emulator test harness"):
> On 22/12/16 14:58, Ian Jackson wrote:
> > "x86emul: in_longmode() should not ignore ->read_msr() errors" aka
> > c/s 122dd9575c7a introduced a use of unlikely() in
> > xen/arch/x86/x86_emulate/x86_emulate.c.
> >
> > I think this is probably intentional and fine.  However, there is no
> > definition of unlikely in the x86 emulator test harness, under tools.
> >
> > The result is this error:
> >    x86_emulate/x86_emulate.c: In function 'in_longmode':
> >    x86_emulate/x86_emulate.c:1300:10: error: implicit declaration of 
> > function 'unlikely' [-Werror=implicit-function-declaration]
> >              unlikely(ops->read_msr(MSR_EFER, &efer, ctxt) != X86EMUL_OKAY) 
> > )
> >              ^~~~~~~~
> >
> > Fix this by providing a boring definition of unlikely().
> >
> > Signed-off-by: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
> 
> This was fixed by 3e84c8da7d2c5442a12789dae7163dca6c0e154f

I did not find this important build fix for a regression in 4.8.0
because:

 * this commit contains a mixture of the build fix and other changes
 * `git log -G unlikely' produced a lot of output: too much to read
   the whole message for each commit through looking for this fix
 * the commit message did not contain a copy of the error message
 * once I had dug into the code myself and found 122dd9575c7a it
   didn't occur to me to `git log --grep 122dd9'.

> Part of that should backported to 4.8, where it is still broken.

Backporting this is made more awkward by the decision to make the fix
a portmanteau.  Do the x86 maintainers intend to provide a
ready-to-use backport or shall I try to prepare one ?

For now, is there any reason why I should not use my change
   +#define unlikely(x) (x)
in an upload to Debian ?

Thanks,
Ian.

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