From: Arnd Bergmann <arnd@arndb.de>
To: Catalin Marinas <catalin.marinas@arm.com>
Subject: Re: [PATCH v6 13/20] arm64: ilp32: share aarch32 syscall wrappers to ilp32
Date: Tue, 22 Dec 2015 22:44:14 +0100
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Cc: Yury Norov <ynorov@caviumnetworks.com>,
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        philipp.tomsich@theobroma-systems.com, joseph@codesourcery.com,
        christoph.muellner@theobroma-systems.com
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On Tuesday 22 December 2015, Catalin Marinas wrote:
> > +
> > +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.

That means we have to set ARCH_PACK_STATFS64 in the arm64 header files
though, and propagate the OABI alignment to arm64/ilp32 as well, rather
than using the 88-byte version that every other 32-bit architecture
except for x86-32 and arm32 has.

Another option would be to set "#define __statfs_word __u64" and use
the 64-bit statfs call, instead of compat_sys_statfs64, but that in turn
requires special-casing statfs in libc.

	Arnd
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