Re: [Qemu-devel] [PATCH] qemu-thread: add TLS wrappers

[Blue Swirl]

On Wed, Aug 17, 2011 at 6:55 AM, Paolo Bonzini <address@hidden> wrote:
> On 08/16/2011 09:36 PM, Brad wrote:
>>
>>> Win32 emulated TLS is slow and is not available on all versions of GCC.
>>> Actually, Win32 does have support for decent TLS, only GCC does not map
>>> __thread to it.  The good news is, it's perfectly possible to declare
>>> TLS variables with simple C code!
>>>
>>> This patch adds wrappers to qemu-thread that will use __thread on POSIX
>>> systems, and the .tls segment on Windows.
>>
>> The actual use of TLS within QEMU on POSIX systems will be optional
>> though, right?
>
> Actually, TLS is already mandatory for both POSIX and Win32 systems.

Not true, we have avoided TLS.

> This patch tries to improve the situation on Windows, both by allowing older
> GCC versions, and by making TLS faster.  On ELF systems, TLS has been
> supported by GCC for perhaps 10 years, there's no reason to care.

GCC may support it but it can't use it on a platform if the other
parts are missing (libc etc.).