linux-kernel - Re: [linux-stable-rc:linux-5.4.y 665/2391] drivers/android/binder.c:3776: Error: unrecognized keyword/register name `l.lwz

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Message-ID: <CAG48ez3VixjDrMnz6+7JjGW_ZLZCD4+dTYWUD_tNOcfEfpu1Bg@mail.gmail.com>
Date:   Thu, 15 Oct 2020 23:46:26 +0200
From:   Jann Horn <jannh@...gle.com>
To:     Jonas Bonn <jonas@...thpole.se>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        Stafford Horne <shorne@...il.com>,
        openrisc@...ts.librecores.org
Cc:     kbuild-all@...ts.01.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Martijn Coenen <maco@...roid.com>,
        kernel test robot <lkp@...el.com>,
        kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [linux-stable-rc:linux-5.4.y 665/2391] drivers/android/binder.c:3776:
 Error: unrecognized keyword/register name `l.lwz

+openrisc folks

On Thu, Oct 15, 2020 at 11:28 PM kernel test robot <lkp@...el.com> wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git linux-5.4.y
> head:   85b0841aab15c12948af951d477183ab3df7de14
> commit: c5665cafbedd2e2a523fe933e452391a02d3adb3 [665/2391] binder: Prevent context manager from incrementing ref 0
> config: openrisc-randconfig-r002-20201014 (attached as .config)
> compiler: or1k-linux-gcc (GCC) 9.3.0
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git/commit/?id=c5665cafbedd2e2a523fe933e452391a02d3adb3
>         git remote add linux-stable-rc https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git
>         git fetch --no-tags linux-stable-rc linux-5.4.y
>         git checkout c5665cafbedd2e2a523fe933e452391a02d3adb3
>         # save the attached .config to linux build tree
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=openrisc
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@...el.com>
>
> All errors (new ones prefixed by >>):
>
>    drivers/android/binder.c: Assembler messages:
> >> drivers/android/binder.c:3776: Error: unrecognized keyword/register name `l.lwz ?ap,4(r25)'
>    drivers/android/binder.c:3781: Error: unrecognized keyword/register name `l.addi ?ap,r0,0'

binder is basically doing this:

u64 data_ptr;
if (get_user(data_ptr, (u64 __user *)ptr))
  return -EFAULT;

and GCC complains that that doesn't turn into valid assembly on
openrisc, where get_user() of size 8 expands into this:

#define __get_user_asm2(x, addr, err)                   \
{                                                       \
        unsigned long long __gu_tmp;                    \
        __asm__ __volatile__(                           \
                "1:     l.lwz %1,0(%2)\n"               \
                "2:     l.lwz %H1,4(%2)\n"              \
                "3:\n"                                  \
                ".section .fixup,\"ax\"\n"              \
                "4:     l.addi %0,r0,%3\n"              \
                "       l.addi %1,r0,0\n"               \
                "       l.addi %H1,r0,0\n"              \
                "       l.j 3b\n"                       \
                "       l.nop\n"                        \
                ".previous\n"                           \
                ".section __ex_table,\"a\"\n"           \
                "       .align 2\n"                     \
                "       .long 1b,4b\n"                  \
                "       .long 2b,4b\n"                  \
                ".previous"                             \
                : "=r"(err), "=&r"(__gu_tmp)            \
                : "r"(addr), "i"(-EFAULT), "0"(err));   \
        (x) = (__typeof__(*(addr)))(                    \
                (__typeof__((x)-(x)))__gu_tmp);         \
}

and apparently the "l.lwz %H1,4(%2)" and "l.addi %H1,r0,0" don't turn
into valid assembly when %H1 expands to "?ap"?

I don't know anything about OpenRISC, but this seems like it's
probably an issue in the get_user() implementation.