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From:   David Laight <David.Laight@ACULAB.COM>
To:     'YiFei Zhu' <zhuyifei1999@gmail.com>,
        "containers@lists.linux-foundation.org" 
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        Dimitrios Skarlatos <dskarlat@cs.cmu.edu>,
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Subject: RE: [PATCH v2 seccomp 2/6] asm/syscall.h: Add syscall_arches[] array
Thread-Topic: [PATCH v2 seccomp 2/6] asm/syscall.h: Add syscall_arches[] array
Thread-Index: AQHWknD17ZW/yCPmvkCTJZb3HlQhMal3ymow
Date:   Thu, 24 Sep 2020 13:47:54 +0000
Message-ID: <7042ba3307b34ce3b95e5fede823514e@AcuMS.aculab.com>
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From: YiFei Zhu 
> Sent: 24 September 2020 13:44
> 
> Seccomp cache emulator needs to know all the architecture numbers
> that syscall_get_arch() could return for the kernel build in order
> to generate a cache for all of them.
> 
> The array is declared in header as static __maybe_unused const
> to maximize compiler optimiation opportunities such as loop
> unrolling.

I doubt the compiler will do what you want.
Looking at it, in most cases there are one or two entries.
I think only MIPS has three.

So a static inline function that contains a list of
conditionals will generate better code that any kind of
array lookup.
For x86-64 you end up with something like:

#ifdef CONFIG_IA32_EMULATION
	if (sd->arch == AUDIT_ARCH_I386) return xxx;
#endif
	return yyy;

Probably saves you having multiple arrays that need to be
kept carefully in step.

	David

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