Re: Support for i386 builds of glibc?

[David Miller <davem at davemloft dot net>]

From: "Maciej W. Rozycki" <macro@codesourcery.com>
Date: Mon, 4 Mar 2013 22:03:59 +0000

> On Mon, 4 Mar 2013, David Miller wrote:
> 
>> > They could be easily emulated with the aid of global spinlocks, but
>> > given the decline of the i386 it's probably not worth the effort.
>> 
>> This is a misnomer, you can't use global spinlocks as those are not
>> signal safe and will deadlock.  Even the glibc testsuite will trigger
>> such deadlocks.
> 
>  I think "can't" is too strong a statement, signals are to userland what 
> interrupts are to the kernel.  The whole critical section could run with 
> all signals blocked; if you wrote that the overhead might be prohibitive, 
> then I would agree though.

You can't mess with signal state in the lock handlers, think about
siglongjmp and friends.

It's impossible even if you're willing to accept prohibitive cost.