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Date: Wed, 26 Oct 2011 16:59:46 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] Make cpu_single_env thread local (Linux
	only for now)
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: "Dr. David Alan Gilbert" <david.gilbert@linaro.org>, agraf@suse.de, Jan Kiszka <jan.kiszka@web.de>, qemu-devel@nongnu.org, patches@linaro.org

On 10/26/2011 04:54 PM, Peter Maydell wrote:
> On 26 October 2011 15:39, Paolo Bonzini<pbonzini@redhat.com>  wrote:
>> On 10/26/2011 04:03 PM, Peter Maydell wrote:
>>>
>>> For the record (since I think we only talked about this on IRC):
>>>   * the POSIX TLS fallback code doesn't work on Linux hosts for
>>>     linux-user emulation (the constructor is never called to set up
>>>     the TLS for the main thread, probably something to do with our
>>>     custom linker script, since it does work OK for system emulation)
>>>   * if I recall correctly from IRC it doesn't compile on OpenBSD
>>>
>>> so for 1.0 perhaps we need to fall back to a simpler set of patches
>>> that just avoid the regression in thread support for linux-user ?
>>
>> I agree.
>
> I was thinking something like a trivial qemu-tls.h which does
>
> #ifdef __linux__
> #define DECLARE_TLS(type, x) extern DEFINE_TLS(type, x)
> #define DEFINE_TLS(type, x)  __thread __typeof__(type) tls__##x
> #define get_tls(x)           tls__##x
> #else
> /* Dummy implementations -- we can get away with this because system
>   * mode is effectively single-threaded for our current limited use of
>   * TLS, and the only -user mode which supports multiple threads is
>   * linux-user.
>   * TODO: proper implementations via Win32 .tls sections and
>   * POSIX pthread_getspecific.
>   */
> #define DECLARE_TLS(type, x) extern DEFINE_TLS(type, x)
> #define DEFINE_TLS(type, x)  __typeof__(type) tls__##x
> #define get_tls(x)           tls__##x
> #endif
>
> and then we can just use your "Make cpu_single_env thread-local"
> patch as-is:
>
> http://git.linaro.org/gitweb?p=people/pmaydell/qemu-arm.git;a=commitdiff;h=b674559fc8a67ae7d30fe3ab3062d5855ac77d2d
>
> (for that matter we could apply the "Prepare Windows port for
> thread-local cpu_single_env" patch too, but that's not a requirement.)

That would be fine.

Paolo