On 8/20/2020 7:47 PM, David Miller wrote:
> From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Date: Fri, 21 Aug 2020 00:37:30 +0100
>
>> On Thu, Aug 20, 2020 at 03:51:22PM -0700, David Miller wrote:
>>> From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
>>> Date: Thu, 20 Aug 2020 20:36:12 +0100
>>>
>>>> We have
>>>> asmlinkage void user_unaligned_trap(struct pt_regs *regs, unsigned int insn)
>>>> {
>>>> enum direction dir;
>>>>
>>>> if(!(current->thread.flags & SPARC_FLAG_UNALIGNED) ||
>>>> (((insn >> 30) & 3) != 3))
>>>> goto kill_user;
>>>>
>>>> there, followed by some work on emulating the insn. So while the default
>>>> behaviour is to hit the process with SIGBUS, it can overridden by setting
>>>> SPARC_FLAG_UNALIGNED in current->thread.flags. Fair enough, but... Just
>>>> what could possibly set that flag?
>>>>
>>>> That stuff had been introduced back in 2.1.9 and even there (or through
>>>> the 2.2, etc.) I don't see anything that would ever set it.
>>>>
>>>> Am I missing something, or had it really been dead code all along?
>>>
>>> Relic from the SunOS and/or Solaris syscall emulation probably.
>>
>> Thought so, but... no such thing in either. And it's not done from assembler -
>> arch/sparc64 used to access ->tss.flags that way (and that was only for
>> SPARC_FLAG_NEWCHILD), but arch/sparc never did...
>>
>> I don't have sunos toolchain to try and build such a binary and test it on
>> a 2.2 kernel, but I would be rather surprised if that had been it.
>>
>> Anyway, it really looks like that's dead code these days...
>
> %100 it is dead code.
This flag would be enabled by trap ST_FIX_ALIGN, fast trap 6, defined
under Software Trap Types in SCD 2.4. From the history, ttable_64.S has never
supported it. Compilers are encouraged to instead support unaligned access
by installing a utrap handler and emulating in userland. Studio on Solaris
generated ST_FIX_ALIGN for 32-bit apps and utrap for 64 bit.
- Steve
