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From: "Michal Suchánek" <msuchanek@suse.de>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michael Neuling <mikey@neuling.org>,
	Madhavan Srinivasan <maddy@linux.vnet.ibm.com>,
	Andrew Donnellan <andrew.donnellan@au1.ibm.com>,
	Arnd Bergmann <arnd@arndb.de>,
	David Hildenbrand <david@redhat.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	linux-kernel@vger.kernel.org, Nicholas Piggin <npiggin@gmail.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Diana Craciun <diana.craciun@nxp.com>,
	Paul Mackerras <paulus@samba.org>, Joel Stanley <joel@jms.id.au>,
	Allison Randal <allison@lohutok.net>,
	Breno Leitao <leitao@debian.org>,
	Firoz Khan <firoz.khan@linaro.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	linuxppc-dev@lists.ozlabs.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Hari Bathini <hbathini@linux.ibm.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH v7 5/6] powerpc/64: Make COMPAT user-selectable disabled on littleendian by default.
Date: Sat, 14 Sep 2019 12:22:02 +0200	[thread overview]
Message-ID: <20190914122202.307707c0@naga> (raw)
In-Reply-To: <87h85us0xy.fsf@mpe.ellerman.id.au>

On Tue, 03 Sep 2019 10:00:57 +1000
Michael Ellerman <mpe@ellerman.id.au> wrote:

> Michal Suchánek <msuchanek@suse.de> writes:
> > On Mon, 02 Sep 2019 12:03:12 +1000
> > Michael Ellerman <mpe@ellerman.id.au> wrote:
> >  
> >> Michal Suchanek <msuchanek@suse.de> writes:  
> >> > On bigendian ppc64 it is common to have 32bit legacy binaries but much
> >> > less so on littleendian.    
> >> 
> >> I think the toolchain people will tell you that there is no 32-bit
> >> little endian ABI defined at all, if anything works it's by accident.  
> >
> > I have seen a piece of software that workarounds code issues on 64bit
> > by always compiling 32bit code. So it does work in some way.  
> 
> What software is that?

The only one I have seen is stockfish (v9)

> 
> > Also it has been pointed out that you can still switch to BE even with
> > the 'fast-switch' removed.  
> 
> Yes we have a proper syscall for endian switching, sys_switch_endian(),
> which is definitely supported.
> 
> But that *only* switches the endian-ness of the process, it does nothing
> to the syscall layer. So any process that switches to the other endian
> must endian flip syscall arguments (that aren't in registers), or flip
> back to the native endian before calling syscalls.

In other words just installing a chroot of binaries built for the other
endian won't work. You need something like qemu to do the syscall
translation or run full VM with a kernel that has the swapped endian
syscall ABI.

Thanks

Michal

  reply	other threads:[~2019-09-14 10:22 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-30 21:03 [PATCH v7 0/6] Disable compat cruft on ppc64le v7 Michal Suchanek
2019-08-30 21:03 ` [PATCH v7 1/6] powerpc: Add back __ARCH_WANT_SYS_LLSEEK macro Michal Suchanek
2019-08-30 21:03 ` [PATCH v7 2/6] powerpc: move common register copy functions from signal_32.c to signal.c Michal Suchanek
2019-08-30 21:03 ` [PATCH v7 3/6] powerpc/perf: consolidate read_user_stack_32 Michal Suchanek
2019-09-02  3:53   ` Michael Ellerman
2019-09-02  4:01     ` Michael Ellerman
2019-09-02  8:26       ` Michal Suchánek
2019-09-02 23:45         ` Michael Ellerman
2019-08-30 21:03 ` [PATCH v7 4/6] powerpc/64: make buildable without CONFIG_COMPAT Michal Suchanek
2019-08-31  6:43   ` Christophe Leroy
2019-08-31 13:02   ` Michal Suchánek
2019-08-30 21:03 ` [PATCH v7 5/6] powerpc/64: Make COMPAT user-selectable disabled on littleendian by default Michal Suchanek
2019-09-02  2:03   ` Michael Ellerman
2019-09-02  9:42     ` Michal Suchánek
2019-09-03  0:00       ` Michael Ellerman
2019-09-14 10:22         ` Michal Suchánek [this message]
2019-09-18  5:36           ` Michael Ellerman
2019-09-02 13:00     ` Segher Boessenkool
2019-09-02 23:53       ` Michael Ellerman
2019-09-03  5:21         ` Christophe Leroy
2019-08-30 21:03 ` [PATCH v7 6/6] powerpc/perf: split callchain.c by bitness Michal Suchanek
2019-08-31 18:51   ` Michal Suchánek
2019-08-31  6:41 ` [PATCH v7 0/6] Disable compat cruft on ppc64le v7 Christophe Leroy
2019-08-31 18:03   ` Michal Suchánek

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