linux-kernel - Re: [PATCH v6 13/20] arm64: ilp32: share aarch32 syscall wrappers to ilp32

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Date:	Tue, 22 Dec 2015 12:25:15 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Yury Norov <ynorov@...iumnetworks.com>
Cc:	arnd@...db.de, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, pinskia@...il.com,
	Prasun.Kapoor@...iumnetworks.com, schwab@...e.de,
	broonie@...nel.org, Nathan_Lynch@...tor.com, agraf@...e.de,
	klimov.linux@...il.com, jan.dakinevich@...il.com,
	ddaney.cavm@...il.com, bamvor.zhangjian@...wei.com,
	philipp.tomsich@...obroma-systems.com, joseph@...esourcery.com,
	christoph.muellner@...obroma-systems.com
Subject: Re: [PATCH v6 13/20] arm64: ilp32: share aarch32 syscall wrappers to
 ilp32

On Wed, Dec 16, 2015 at 12:42:39AM +0300, Yury Norov wrote:
> statfs64, fstat64 and mmap_pgoff has wrappers that needed both by aarch32 and
> ilp32 to workaround some issues. Here we create common file to share aarch32
> workarounds to with ilp32 code.
[...]
> --- /dev/null
> +++ b/arch/arm64/kernel/entry32-common.S
> @@ -0,0 +1,37 @@
> +#include <linux/linkage.h>
> +#include <linux/const.h>
> +
> +#include <asm/assembler.h>
> +#include <asm/asm-offsets.h>
> +#include <asm/errno.h>
> +#include <asm/page.h>
> +
> +ENTRY(compat_sys_statfs64_wrapper)
> +	mov	w3, #84
> +	cmp	w1, #88
> +	csel	w1, w3, w1, eq
> +	b	compat_sys_statfs64
> +ENDPROC(compat_sys_statfs64_wrapper)
> +
> +ENTRY(compat_sys_fstatfs64_wrapper)
> +	mov	w3, #84
> +	cmp	w1, #88
> +	csel	w1, w3, w1, eq
> +	b	compat_sys_fstatfs64
> +ENDPROC(compat_sys_fstatfs64_wrapper)

I'm not convinced we need these wrappers for ILP32. They've been
introduced on arch/arm many years ago by commit Fixes: 713c481519f1
([ARM] 3108/2: old ABI compat: statfs64 and fstatfs64) to deal with user
space passing a size of 88 (the EABI size of struct compat_statfs64
without the packing and alignment attribute). Since that commit, the
sizeof(struct compat_statfs64) is 84 already. This should be the case
with the new ILP32 exported headers (no backwards compatibility), so
user space should never pass 88 as size. Therefore we could call
compat_sys_(f)statfs64 directly without wrappers.

-- 
Catalin
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