Re: [RFC -tip 2/4] x86: uaccess: introduce __{get|put}_user exception handling framework

[Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>]

Brian Gerst wrote:
> On Tue, Dec 23, 2008 at 12:22 AM, Hiroshi Shimamoto
> <h-shimamoto@ct.jp.nec.com> wrote:
>> From: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
>>
>> Impact: introduce new framework
>>
>> Introduce exception handling framework.
>> __{get|put}_user_ex_try() begins exception block and
>> __{get|put}_user_ex_catch() ends block and if an exception occurred in this
>> block using __{get|put}_user_ex, direct jump to __{get|put}_user_ex_catch()
>> and err is set to specified value.
> 
> You shouldn't do this.  According to the gcc manual[1], "Speaking of
> labels, jumps from one asm to another are not supported. The
> compiler's optimizers do not know about these jumps, and therefore
> they cannot take account of them when deciding how to optimize."
> 
> [1] http://gcc.gnu.org/onlinedocs/gcc-4.3.2/gcc/Extended-Asm.html
> 
thanks so much for this information!
I didn't know about this and it's what I want to know, thinking
about this series.

Thanks,
Hiroshi