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

Josh Poimboeuf
2021-11-04T22:32:00Z

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.

Could we just use EX_TYPE_EFAULT_REG?

--
Josh