ARM64: Disabling warnings about deprecated armv8 instructions
Michael Zoran
mzoran at crowfest.net
Sun Jan 22 03:05:15 PST 2017
On Sun, 2017-01-22 at 10:54 +0000, Ard Biesheuvel wrote:
> On 22 January 2017 at 09:52, Michael Zoran <mzoran at crowfest.net>
> wrote:
> > On Sun, 2017-01-22 at 09:43 +0000, Ard Biesheuvel wrote:
> > > On 22 January 2017 at 09:38, Michael Zoran <mzoran at crowfest.net>
> > > wrote:
> > > > On Sun, 2017-01-22 at 17:05 +0800, Jisheng Zhang wrote:
> > > > > On Sun, 22 Jan 2017 00:58:48 -0800 Michael Zoran wrote:
> > > > >
> > > > > > On Sun, 2017-01-22 at 09:52 +0100, Alexander Stein wrote:
> > > > > > > Hi Michael,
> > > > > > >
> > > > > > > On Sunday, January 22, 2017, 12:07:04 AM CET Michael
> > > > > > > Zoran
> > > > > > > wrote:
> > > > > > > > I'm not sure if this if the correct place to be asking
> > > > > > > > this. The
> > > > > > > > RPI
> > > > > > > > 3 running ARM64 is slowly reaching the point of being
> > > > > > > > about
> > > > > > > > to
> > > > > > > > seriously run a 32 bit vender OS like Raspbian. When
> > > > > > > > running
> > > > > > > > Raspbian,
> > > > > > > > I'm seeing a very large number(thousands) of kernel log
> > > > > > > > messages
> > > > > > > > about
> > > > > > > > deprecated instructions especially setend and barrier
> > > > > > > > instuctions.
> > > > > > > > This can be very annoying and is completely filling the
> > > > > > > > kernel
> > > > > > > > log.
> > > > > > > >
> > > > > > > > I'm considering submitting a patch to add a Kconfig
> > > > > > > > option
> > > > > > > > to
> > > > > > > > disable
> > > > > > > > these warnings with the default being to keep the
> > > > > > > > warnings
> > > > > > > > enabled. I
> > > > > > > > was wondering if such a patch could be seriously
> > > > > > > > considered.
> > > > > > >
> > > > > > > Could you please provide an example of those warning an
> > > > > > > what
> > > > > > > is
> > > > > > > trigging
> > > > > > > those?
> > > > > > >
> > > > > > > Thanks and best regards,
> > > > > > > Alexander
> > > > > >
> > > > > > Sure, here is a snipped from dmesg. I think this is
> > > > > > happening
> > > > > > because
> > > > > > the entire Raspbian OS is compiled with a custom gcc
> > > > > > compiler
> > > > > > that
> > > > > > is
> > > > > > targeting arm6+VFP.
> > > > >
> > > > > IMHO, this is the root cause. I didn't see below warnings
> > > > > from
> > > > > dmesg
> > > > > with
> > > > > armhf debian and ubuntu If the underlying HW is armv8
> > > > > compatible,
> > > > > it
> > > > > doesn't make sense to target the compiler to armv6
> > > > >
> > > > >
> > > >
> > > > Advanced users can install a different OS. Beginners can't and
> > > > will
> > > > need a single OS image for simple install.
> > > >
> > >
> > > That single OS image can simply test for the presence of
> > > /proc/sys/abi, and perform the writes if it is there.
> > >
> > > > Does anybody know if these instructions are detected at
> > > > runtime?
> > >
> > > What do you mean by 'detected'?
> > >
> > > > I'm
> > > > also looking into an issue with Mathmatica due to broken OS
> > > > detection.
> > > > It appears that arm64 is currently missing some of the CPU
> > > > spoofing
> > > > that happens on other architectures...
> > > >
> > >
> > > Could you elaborate? What do you think should be there that
> > > isn't?
> >
> > I'm saying that when running a ELF32 executable, the system needs
> > to
> > fake the CPU architecture according to the uname system API and
> > /proc/cpuinfo.
> >
> > Today, I run uname -a in Raspbian and I get aarch64. I want it to
> > display arm6l or whatever to get Mathematica to load.
> >
> > I see some code to make this work on other architectures such as
> > X86,
> > but most of this appears to be unimplemented on arm64.
> >
>
> Did you try linux32?
>
> pi at raspberrypi:~$ uname -a
> Linux raspberrypi 4.10.0-rc3-v8+ #3 SMP PREEMPT Sun Jan 15 15:22:12
> WET 2017 aarch64 GNU/Linux
> pi at raspberrypi:~ $ linux32 uname -a
> Linux raspberrypi 4.10.0-rc3-v8+ #3 SMP PREEMPT Sun Jan 15 15:22:12
> WET 2017 armv8l GNU/Linux
>
> If the app in question cannot deal with the armv8l personality, the
> app should be fixed instead.
Thanks, I didn't know about the tool.
I'm looking at the code in arch/arm64/include/asm/elf.h. I'm looking at
the COMPAT_SET_PERSONALITY macro. It appears to be broken. It seems
like it should have a call to set_personality with PER_LINUX32.
If I look in include/uapi/linux/personality.h, I see some very
interesting things. Quite the complex set of options I would say.
/*
* Flags for bug emulation.
*
* These occupy the top three bytes.
*/
enum {
UNAME26 = 0x0020000,
ADDR_NO_RANDOMIZE = 0x0040000, /* disable
randomization of VA space */
FDPIC_FUNCPTRS = 0x0080000, /* userspace function
ptrs point to descriptors
* (signal handling)
*/
MMAP_PAGE_ZERO = 0x0100000,
ADDR_COMPAT_LAYOUT = 0x0200000,
READ_IMPLIES_EXEC = 0x0400000,
ADDR_LIMIT_32BIT = 0x0800000,
SHORT_INODE = 0x1000000,
WHOLE_SECONDS = 0x2000000,
STICKY_TIMEOUTS = 0x4000000,
ADDR_LIMIT_3GB = 0x8000000,
};
/*
* Security-relevant compatibility flags that must be
* cleared upon setuid or setgid exec:
*/
#define PER_CLEAR_ON_SETID (READ_IMPLIES_EXEC | \
ADDR_NO_RANDOMIZE | \
ADDR_COMPAT_LAYOUT | \
MMAP_PAGE_ZERO)
/*
* Personality types.
*
* These go in the low byte. Avoid using the top bit, it will
* conflict with error returns.
*/
enum {
PER_LINUX = 0x0000,
PER_LINUX_32BIT = 0x0000 | ADDR_LIMIT_32BIT,
PER_LINUX_FDPIC = 0x0000 | FDPIC_FUNCPTRS,
PER_SVR4 = 0x0001 | STICKY_TIMEOUTS |
MMAP_PAGE_ZERO,
PER_SVR3 = 0x0002 | STICKY_TIMEOUTS |
SHORT_INODE,
PER_SCOSVR3 = 0x0003 | STICKY_TIMEOUTS |
WHOLE_SECONDS | SHORT_INODE,
PER_OSR5 = 0x0003 | STICKY_TIMEOUTS |
WHOLE_SECONDS,
PER_WYSEV386 = 0x0004 | STICKY_TIMEOUTS |
SHORT_INODE,
PER_ISCR4 = 0x0005 | STICKY_TIMEOUTS,
PER_BSD = 0x0006,
PER_SUNOS = 0x0006 | STICKY_TIMEOUTS,
PER_XENIX = 0x0007 | STICKY_TIMEOUTS |
SHORT_INODE,
PER_LINUX32 = 0x0008,
PER_LINUX32_3GB = 0x0008 | ADDR_LIMIT_3GB,
PER_IRIX32 = 0x0009 | STICKY_TIMEOUTS,/* IRIX5
32-bit */
PER_IRIXN32 = 0x000a | STICKY_TIMEOUTS,/* IRIX6
new 32-bit */
PER_IRIX64 = 0x000b | STICKY_TIMEOUTS,/* IRIX6
64-bit */
PER_RISCOS = 0x000c,
PER_SOLARIS = 0x000d | STICKY_TIMEOUTS,
PER_UW7 = 0x000e | STICKY_TIMEOUTS |
MMAP_PAGE_ZERO,
PER_OSF4 = 0x000f, /*
OSF/1 v4 */
PER_HPUX = 0x0010,
PER_MASK = 0x00ff,
};
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