Re: [PATCH 3/3] linux-user/i386: Emulate x86_64 vsyscalls

From: "Alex Bennée" <alex.bennee@linaro.org>
To: Richard Henderson <richard.henderson@linaro.org>
Cc: qemu-devel@nongnu.org, pbonzini@redhat.com, riku.voipio@iki.fi,
	laurent@vivier.eu, peter.maydell@linaro.org
Subject: Re: [PATCH 3/3] linux-user/i386: Emulate x86_64 vsyscalls
Date: Thu, 16 Jan 2020 20:15:04 +0000	[thread overview]
Message-ID: <87d0bjkvjr.fsf@linaro.org> (raw)
In-Reply-To: <3733f2cd-9262-d7f9-ab9c-c8a3032732df@linaro.org>

Richard Henderson <richard.henderson@linaro.org> writes:

> On 1/16/20 6:26 AM, Alex Bennée wrote:
>>> +    /*
>>> +     * Perform the syscall.  None of the vsyscalls should need restarting,
>>> +     * and all faults should have been caught above.
>>> +     */
>>> +    ret = do_syscall(env, syscall, env->regs[R_EDI], env->regs[R_ESI],
>>> +                     env->regs[R_EDX], env->regs[10], env->regs[8],
>>> +                     env->regs[9], 0, 0);
>> 
>> How come the register ABI to the syscall is different to the others. I
>> can see why syscall doesn't come from EAX but the others are a different
>> set to normal syscalls which might be why:
>
> Cut and paste error, I assume.
>
> That said, the three syscalls have a maximum of 2 arguments,
> so I could really just pass EDI and ESI and 0 for the rest...
>
>> I'm seeing a EFAULT on the gettimeofday failure:
>
> What getttimeofday failure?  Is this related to the mention of /sbin/ldconfig
> in your previous message?

No - the buster x86064 ldconfig seg is unrelated to this series. It has
however spawned an additional bug in gdbstub while it was at it ;-)

>
>>    #0  do_syscall (cpu_env=cpu_env@entry=0x5555577d2b10, num=num@entry=96, arg1=0, arg2=0, arg3=4211016, arg4=8, arg5=274888677184, arg6=274886295415, arg7=0, arg8=0) at /home/alex/lsrc/qemu.git/linux-user/syscall.c:12076                                               
>>    #1  0x0000555555609b6e in emulate_vsyscall (env=0x5555577d2b10) at /home/alex/lsrc/qemu.git/linux-user/x86_64/../i386/cpu_loop.c:180
>>    #2  cpu_loop (env=0x5555577d2b10) at /home/alex/lsrc/qemu.git/linux-user/x86_64/../i386/cpu_loop.c:246                              
>>    #3  0x000055555559640e in main (argc=<optimized out>, argv=<optimized
>>    #out>, envp=<optimized out>) at
>>    #/home/alex/lsrc/qemu.git/linux-user/main.c:865
>> 
>> arg1/arg2 don't seem right here.
>
> Why?  NULL value for arg1 is legal, though semi-useless.
>
> Ah, I see that our implementation of gettimeofday doesn't honor NULL.
>
>
> r~

-- 
Alex Bennée