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Re: [PATCH v2 3/5] linux-user/i386: Emulate x86_64 vsyscalls
From: |
Alex Bennée |
Subject: |
Re: [PATCH v2 3/5] linux-user/i386: Emulate x86_64 vsyscalls |
Date: |
Tue, 21 Jan 2020 16:15:55 +0000 |
User-agent: |
mu4e 1.3.6; emacs 28.0.50 |
Richard Henderson <address@hidden> writes:
> On 1/21/20 12:13 AM, Alex Bennée wrote:
>>
>> Richard Henderson <address@hidden> writes:
>>
>>> On 1/20/20 1:48 AM, Alex Bennée wrote:
>>>>> + default:
>>>>> + sigsegv:
>>>>
>>>> this label looks a little extraneous.
>>>>
>>>> Otherwise:
>>>>
>>>> Reviewed-by: Alex Bennée <address@hidden>
>>>>
>>>
>>> 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
[PATCH v2 4/5] linux-user: Add x86_64 vsyscall page to /proc/self/maps, Richard Henderson, 2020/01/16
[PATCH v2 5/5] linux-user: Flush out implementation of gettimeofday, Richard Henderson, 2020/01/16
Re: [PATCH v2 0/5] linux-user: Implement x86_64 vsyscalls, Richard Henderson, 2020/01/16
Re: [PATCH v2 0/5] linux-user: Implement x86_64 vsyscalls, Laurent Vivier, 2020/01/28