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From: "Alex Bennée" <alex.bennee@linaro.org>
To: Richard Henderson <richard.henderson@linaro.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	qemu-devel@nongnu.org, laurent@vivier.eu
Subject: Re: [PATCH v2 3/5] linux-user/i386: Emulate x86_64 vsyscalls
Date: Tue, 21 Jan 2020 16:15:55 +0000
Message-ID: <87a76g23b8.fsf@linaro.org> (raw)
In-Reply-To: <e383d1d6-7c08-ba3c-6e8b-971d62a9d2cb@linaro.org>


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

> On 1/21/20 12:13 AM, Alex Bennée wrote:
>> 
>> Richard Henderson <richard.henderson@linaro.org> writes:
>> 
>>> On 1/20/20 1:48 AM, Alex Bennée wrote:
>>>>> +    default:
>>>>> +    sigsegv:
>>>>
>>>> this label looks a little extraneous.
>>>>
>>>> Otherwise:
>>>>
>>>> Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
>>>>
>>>
>>> Look a little further down:
>>>
>>>> +    default:
>>>> +    sigsegv:
>>>> +        /* Like force_sig(SIGSEGV).  */
>>>> +        gen_signal(env, TARGET_SIGSEGV, TARGET_SI_KERNEL, 0);
>>>> +        return;
>>>> +    }
>>>> +
>>>> +    /*
>>>> +     * Validate the return address.
>>>> +     * Note that the kernel treats this the same as an invalid entry point.
>>>> +     */
>>>> +    if (get_user_u64(caller, env->regs[R_ESP])) {
>>>> +        goto sigsegv;
>>>> +    }
>> 
>> Wouldn't this read better:
>> 
>>     /*
>>      * Validate the entry point.  We have already validated the page
>>      * during translation, now verify the offset.
>>      */
>>     switch (env->eip & ~TARGET_PAGE_MASK) {
>>     case 0x000:
>>         syscall = TARGET_NR_gettimeofday;
>>         break;
>>     case 0x400:
>>         syscall = TARGET_NR_time;
>>         break;
>>     case 0x800:
>>         syscall = TARGET_NR_getcpu;
>>         break;
>>     default:
>>         syscall = -1;
>>         break;
>>     }
>> 
>>     /*
>>      * If we have an invalid entry point or an invalid return address we
>>      * generate a SIGSEG.
>>      */
>>     if (syscall < 0 || get_user_u64(caller, env->regs[R_ESP])) {
>>         gen_signal(env, TARGET_SIGSEGV, TARGET_SI_KERNEL, 0);
>>         return;
>>     }
>> 
>
> Only if you have a violent goto allergy.

gotos have their place but jumping backwards is confusing to eye. If the
compiler want to mess with layout after then it is free to do so.

-- 
Alex Bennée


  reply index

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-16 19:43 [PATCH v2 0/5] linux-user: Implement " Richard Henderson
2020-01-16 19:43 ` [PATCH v2 1/5] target/i386: Renumber EXCP_SYSCALL Richard Henderson
2020-01-16 19:43 ` [PATCH v2 2/5] linux-user/i386: Split out gen_signal Richard Henderson
2020-01-16 19:43 ` [PATCH v2 3/5] linux-user/i386: Emulate x86_64 vsyscalls Richard Henderson
2020-01-20 11:48   ` Alex Bennée
2020-01-21  3:38     ` Richard Henderson
2020-01-21 10:13       ` Alex Bennée
2020-01-21 15:51         ` Richard Henderson
2020-01-21 16:15           ` Alex Bennée [this message]
2020-01-21 16:23             ` Paolo Bonzini
2020-01-16 19:43 ` [PATCH v2 4/5] linux-user: Add x86_64 vsyscall page to /proc/self/maps Richard Henderson
2020-01-17  6:39   ` Philippe Mathieu-Daudé
2020-01-20 14:41   ` Alex Bennée
2020-01-16 19:43 ` [PATCH v2 5/5] linux-user: Flush out implementation of gettimeofday Richard Henderson
2020-01-17  6:37   ` Philippe Mathieu-Daudé
2020-01-20 13:27   ` Alex Bennée
2020-01-16 19:46 ` [PATCH v2 0/5] linux-user: Implement x86_64 vsyscalls Richard Henderson
2020-01-28 17:26 ` Laurent Vivier

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