From: Peter Zijlstra <peterz@infradead.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
mark.rutland@arm.com, dvyukov@google.com, seanjc@google.com,
pbonzini@redhat.com, mbenes@suse.cz
Subject: Re: [PATCH 20/22] x86,word-at-a-time: Remove .fixup usage
Date: Fri, 5 Nov 2021 19:07:19 +0100 [thread overview]
Message-ID: <20211105180719.GM174703@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20211105180152.oi7h3p6fb6c5pjkf@treble>
On Fri, Nov 05, 2021 at 11:01:52AM -0700, Josh Poimboeuf wrote:
> On Fri, Nov 05, 2021 at 06:10:43PM +0100, Peter Zijlstra wrote:
> > +#ifdef CONFIG_CC_HAS_ASM_GOTO_OUTPUT
> > +
> > +static inline unsigned long load_unaligned_zeropad(const void *addr)
> > +{
> > + unsigned long offset, data;
> > + unsigned long ret;
> > +
> > + asm_volatile_goto(
> > + "1: mov %[mem], %[ret]\n"
> > +
> > + _ASM_EXTABLE(1b, %l[do_exception])
> > +
> > + : [ret] "=&r" (ret)
> > + : [mem] "m" (*(unsigned long *)addr)
> > + : : do_exception);
> > +
> > +out:
> > + return ret;
> > +
> > +do_exception: __cold;
> > +
> > + offset = (unsigned long)addr & (sizeof(long) - 1);
> > + addr = (void *)((unsigned long)addr & ~(sizeof(long) - 1));
> > + data = *(unsigned long *)addr;
> > + ret = data >> offset * 8;
> > + goto out;
>
> Superfluous goto, can just return here?
Can do I suppose.
> > static inline unsigned long load_unaligned_zeropad(const void *addr)
> > {
> > - unsigned long ret, dummy;
> > + unsigned long offset, data;
> > + unsigned long ret, err = 0;
> >
> > - asm(
> > - "1:\tmov %2,%0\n"
> > + asm( "1: mov %[mem], %[ret]\n"
> > "2:\n"
> > - ".section .fixup,\"ax\"\n"
> > - "3:\t"
> > - "lea %2,%1\n\t"
> > - "and %3,%1\n\t"
> > - "mov (%1),%0\n\t"
> > - "leal %2,%%ecx\n\t"
> > - "andl %4,%%ecx\n\t"
> > - "shll $3,%%ecx\n\t"
> > - "shr %%cl,%0\n\t"
> > - "jmp 2b\n"
> > - ".previous\n"
> > - _ASM_EXTABLE(1b, 3b)
> > - :"=&r" (ret),"=&c" (dummy)
> > - :"m" (*(unsigned long *)addr),
> > - "i" (-sizeof(unsigned long)),
> > - "i" (sizeof(unsigned long)-1));
> > +
> > + _ASM_EXTABLE_FAULT(1b, 2b)
> > +
> > + : [ret] "=&r" (ret), "+a" (err)
> > + : [mem] "m" (*(unsigned long *)addr));
> > +
> > + if (unlikely(err)) {
> > + offset = (unsigned long)addr & (sizeof(long) - 1);
> > + addr = (void *)((unsigned long)addr & ~(sizeof(long) - 1));
> > + data = *(unsigned long *)addr;
> > + ret = data >> offset * 8;
> > + }
> > +
> > return ret;
>
> This adds a (normally not taken) conditional jump, would a straight jmp
> over the fixup not be better?
>
> i.e.
>
> 1: mov %[mem], %[ret]
> jmp 2
> ... fixup code ...
> 2:
I really don't know, this way we can get the bulk of the text
out-of-line.
next prev parent reply other threads:[~2021-11-05 18:10 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-05 17:10 [PATCH 00/22] x86: Remove anonymous out-of-line fixups Peter Zijlstra
2021-11-05 17:10 ` [PATCH 01/22] bitfield.h: Fix "type of reg too small for mask" test Peter Zijlstra
2021-11-05 17:10 ` [PATCH 02/22] x86,mmx_32: Remove .fixup usage Peter Zijlstra
2021-11-05 17:10 ` [PATCH 03/22] x86,copy_user_64: " Peter Zijlstra
2021-11-05 17:10 ` [PATCH 04/22] x86,copy_mc_64: " Peter Zijlstra
2021-11-05 17:10 ` [PATCH 05/22] x86,entry_64: " Peter Zijlstra
2021-11-05 17:10 ` [PATCH 06/22] x86,entry_32: " Peter Zijlstra
2021-11-05 17:10 ` [PATCH 07/22] x86,extable: Extend extable functionality Peter Zijlstra
2021-11-05 17:10 ` [PATCH 08/22] x86,msr: Remove .fixup usage Peter Zijlstra
2021-11-05 17:10 ` [PATCH 09/22] x86,futex: " Peter Zijlstra
2021-11-05 17:10 ` [PATCH 10/22] x86,uaccess: " Peter Zijlstra
2021-11-05 17:10 ` [PATCH 11/22] x86,xen: " Peter Zijlstra
2021-11-05 17:10 ` [PATCH 12/22] x86,fpu: " Peter Zijlstra
2021-11-05 17:10 ` [PATCH 13/22] x86,segment: " Peter Zijlstra
2021-11-05 17:10 ` [PATCH 14/22] x86,vmx: " Peter Zijlstra
2021-11-05 17:10 ` [PATCH 15/22] x86,checksum_32: " Peter Zijlstra
2021-11-05 17:10 ` [PATCH 16/22] x86,sgx: " Peter Zijlstra
2021-11-05 17:10 ` [PATCH 17/22] x86,kvm: " Peter Zijlstra
2021-11-05 17:10 ` [PATCH 18/22] x86,usercopy_32: Simplify __copy_user_intel_nocache() Peter Zijlstra
2021-11-05 17:10 ` [PATCH 19/22] x86,usercopy: Remove .fixup usage Peter Zijlstra
2021-11-05 17:10 ` [PATCH 20/22] x86,word-at-a-time: " Peter Zijlstra
2021-11-05 18:01 ` Josh Poimboeuf
2021-11-05 18:07 ` Peter Zijlstra [this message]
2021-11-08 16:47 ` Josh Poimboeuf
2021-11-08 18:29 ` Peter Zijlstra
2021-11-08 18:53 ` Nick Desaulniers
2021-11-09 8:23 ` Peter Zijlstra
2021-11-09 19:22 ` Nick Desaulniers
2021-11-09 20:59 ` Bill Wendling
2021-11-09 21:21 ` Peter Zijlstra
2021-11-09 21:25 ` Nick Desaulniers
2021-11-09 22:11 ` Peter Zijlstra
2021-11-09 22:15 ` Nick Desaulniers
2021-11-09 21:07 ` Peter Zijlstra
2021-11-10 10:18 ` Peter Zijlstra
2021-11-10 10:46 ` David Laight
2021-11-10 11:09 ` Peter Zijlstra
2021-11-10 12:20 ` David Laight
2021-11-12 1:50 ` Josh Poimboeuf
2021-11-12 9:33 ` Peter Zijlstra
2021-11-13 5:35 ` Josh Poimboeuf
2021-11-15 12:36 ` Miroslav Benes
2021-11-15 13:01 ` Joe Lawrence
2021-11-15 23:40 ` Josh Poimboeuf
2021-11-16 7:25 ` Miroslav Benes
2021-11-15 12:59 ` Miroslav Benes
2021-11-16 21:27 ` Josh Poimboeuf
2021-11-18 7:15 ` Miroslav Benes
2021-11-22 17:46 ` Petr Mladek
2021-11-24 17:42 ` Josh Poimboeuf
2021-11-25 8:18 ` Petr Mladek
2021-11-10 12:14 ` Segher Boessenkool
2021-11-05 17:10 ` [PATCH 21/22] x86: Remove .fixup section Peter Zijlstra
2021-11-05 17:10 ` [PATCH 22/22] objtool: Remove .fixup handling Peter Zijlstra
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