Re: [RFC][PATCH 11/22] x86,xen: Remove .fixup usage

Peter Zijlstra
2021-11-05T07:57:05Z

On Thu, Nov 04, 2021 at 03:31:51PM -0700, Josh Poimboeuf wrote:
> On Thu, Nov 04, 2021 at 05:47:40PM +0100, Peter Zijlstra wrote:
> > Employ the fancy new EX_TYPE_IMM_REG to create EX_TYPE_NEG_REG to
> > store '-1' into the designated register and use this to remove some
> > Xen .fixup usage.
> >
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > ---
> > arch/x86/include/asm/extable_fixup_types.h | 1 +
> > arch/x86/include/asm/xen/page.h | 12 ++----------
> > 2 files changed, 3 insertions(+), 10 deletions(-)
> >
> > --- a/arch/x86/include/asm/extable_fixup_types.h
> > +++ b/arch/x86/include/asm/extable_fixup_types.h
> > @@ -35,5 +35,6 @@
> >
> > #define EX_TYPE_IMM_REG 17 /* reg := (long)imm */
> > #define EX_TYPE_EFAULT_REG (EX_TYPE_IMM_REG | EX_TYPE_IMM(-EFAULT))
> > +#define EX_TYPE_NEG_REG (EX_TYPE_IMM_REG | EX_TYPE_IMM(-1))
> >
> > #endif
> > --- a/arch/x86/include/asm/xen/page.h
> > +++ b/arch/x86/include/asm/xen/page.h
> > @@ -96,11 +96,7 @@ static inline int xen_safe_write_ulong(u
> >
> > asm volatile("1: mov %[val], %[ptr]\n"
> > "2:\n"
> > - ".section .fixup, \"ax\"\n"
> > - "3: sub $1, %[ret]\n"
> > - " jmp 2b\n"
> > - ".previous\n"
> > - _ASM_EXTABLE(1b, 3b)
> > + _ASM_EXTABLE_TYPE_REG(1b, 2b, EX_TYPE_NEG_REG, %[ret])
> > : [ret] "+r" (ret), [ptr] "=m" (*addr)
> > : [val] "r" (val));
> >
> > @@ -115,11 +111,7 @@ static inline int xen_safe_read_ulong(co
> >
> > asm volatile("1: mov %[ptr], %[rval]\n"
> > "2:\n"
> > - ".section .fixup, \"ax\"\n"
> > - "3: sub $1, %[ret]\n"
> > - " jmp 2b\n"
> > - ".previous\n"
> > - _ASM_EXTABLE(1b, 3b)
> > + _ASM_EXTABLE_TYPE_REG(1b, 2b, EX_TYPE_NEG_REG, %[ret])
> > : [ret] "+r" (ret), [rval] "+r" (rval)
> > : [ptr] "m" (*addr));
> > *val = rval;
>
> -EFAULT is also negative, and presumably more appropriate than -1.

Possibly, means I'll have to go audit all it's users. I'll put it on the
todo list.