It's also has a race condition.
Please see
https://lore.kernel.org/qemu-devel/20221206041715.314209-18-richard.hender...@linaro.org/
r~
On Thu, 15 Dec 2022, 13:33 Michael Tokarev, <m...@tls.msk.ru> wrote:
> 04.10.2022 22:52, Richard Henderson wrote:
> > From: Leandro Lupori <leandro.lup...@eldorado.org.br>
> >
> > PowerPC64 processors handle direct branches better than indirect
> > ones, resulting in less stalled cycles and branch misses.
> >
> > However, PPC's tb_target_set_jmp_target() was only using direct
> > branches for 16-bit jumps, while PowerPC64's unconditional branch
> > instructions are able to handle displacements of up to 26 bits.
> > To take advantage of this, now jumps whose displacements fit in
> > between 17 and 26 bits are also converted to direct branches.
> >
> > Reviewed-by: Richard Henderson <richard.hender...@linaro.org>
> > Signed-off-by: Leandro Lupori <leandro.lup...@eldorado.org.br>
> > [rth: Expanded some commentary.]
> > Signed-off-by: Richard Henderson <richard.hender...@linaro.org>
> > ---
> > tcg/ppc/tcg-target.c.inc | 119 +++++++++++++++++++++++++++++----------
> > 1 file changed, 88 insertions(+), 31 deletions(-)
> >
> > diff --git a/tcg/ppc/tcg-target.c.inc b/tcg/ppc/tcg-target.c.inc
> > index 1cbd047ab3..e3dba47697 100644
> > --- a/tcg/ppc/tcg-target.c.inc
> > +++ b/tcg/ppc/tcg-target.c.inc
> ...
>
> > + /*
> > + * There's no convenient way to get the compiler to allocate a pair
> > + * of registers at an even index, so copy into r6/r7 and clobber.
> > + */
> > + asm("mr %%r6, %1\n\t"
> > + "mr %%r7, %2\n\t"
> > + "stq %%r6, %0"
> > + : "=Q"(*(__int128 *)rw) : "r"(p[0]), "r"(p[1]) : "r6", "r7");
>
> This is the only place in qemu where __int128 is used (other places name
> it __int128_t), and is used *unconditionally*. Is it right?
>
> In particular, this breaks compilation on powerpc:
>
> cc -m32 -Ilibqemu-aarch64-softmmu.fa.p... -c ../../tcg/tcg.c
> In file included from ../../tcg/tcg.c:432:
> /<<PKGBUILDDIR>>/tcg/ppc/tcg-target.c.inc: In function ‘ppc64_replace4’:
> /<<PKGBUILDDIR>>/tcg/ppc/tcg-target.c.inc:1885:18: error: expected
> expression before ‘__int128’
> 1885 | : "=Q"(*(__int128 *)rw) : "r"(p[0]), "r"(p[1]) : "r6",
> "r7");
> | ^~~~~~~~
> /<<PKGBUILDDIR>>/tcg/ppc/tcg-target.c.inc:1885:29: error: expected ‘)’
> before ‘rw’
> 1885 | : "=Q"(*(__int128 *)rw) : "r"(p[0]), "r"(p[1]) : "r6",
> "r7");
> | ~ ^~
>
> Thanks,
>
> /mjt
>
