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Date:   Sun, 05 Feb 2023 10:55:38 +0100
From:   "Arnd Bergmann" <arnd@arndb.de>
To:     "Nhat Pham" <nphamcs@gmail.com>,
        "Andrew Morton" <akpm@linux-foundation.org>
Cc:     "Johannes Weiner" <hannes@cmpxchg.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, bfoster@redhat.com,
        "Matthew Wilcox" <willy@infradead.org>, linux-api@vger.kernel.org,
        kernel-team@meta.com
Subject: Re: [PATCH v9 2/3] cachestat: implement cachestat syscall
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On Fri, Feb 3, 2023, at 20:04, Nhat Pham wrote:

> +SYSCALL_DEFINE5(cachestat, unsigned int, fd, loff_t, off, size_t, len,
> +		struct cachestat __user *, cstat, unsigned int, flags)
> +{
> +	return ksys_cachestat(fd, off, len, cstat, flags);
> +}
> +
> +#ifdef CONFIG_COMPAT
> +COMPAT_SYSCALL_DEFINE6(cachestat, unsigned int, fd, 
> compat_arg_u64_dual(off),
> +		size_t, len, struct cachestat __user *, cstat, unsigned int, flags)
> +{
> +	return ksys_cachestat(fd, compat_arg_u64_glue(off), len, cstat, 
> flags);
> +}

This still looks wrong to me, as this compat definition does not match
the native variant on architectures that require 64-bit arguments to
be passed in aligned register pairs, such as arm, mips or ppc, but
not x86, s390 or riscv.

     Arnd