Re: [Qemu-devel] [PATCH v2 1/3] qemu-tls.h: Add abstraction layer for TLS variables

[Andreas Färber]

Am 27.10.2011 13:37, schrieb Peter Maydell:
> Add an abstraction layer for defining and using thread-local
> variables. For the moment this is implemented only for Linux,
> which means they can only be used in restricted circumstances.
> The abstraction layer allows us to add POSIX and Win32 support
> later.
> 

[Paolo's SoB missing]

> Signed-off-by: Peter Maydell <address@hidden>
> ---
>  qemu-tls.h |   51 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 51 insertions(+), 0 deletions(-)
>  create mode 100644 qemu-tls.h
> 
> diff --git a/qemu-tls.h b/qemu-tls.h
> new file mode 100644
> index 0000000..d96a159
> --- /dev/null
> +++ b/qemu-tls.h
> @@ -0,0 +1,51 @@
> +/*
> + * Abstraction layer for defining and using TLS variables
> + *
> + * Copyright (c) 2011 Red Hat, Inc, Linaro Limited

The concatenation looks kind of funny. ;)

> + *
> + * Authors:
> + *  Paolo Bonzini <address@hidden>
> + *  Peter Maydell <address@hidden>
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License as
> + * published by the Free Software Foundation; either version 2 of
> + * the License, or (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License along
> + * with this program; if not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#ifndef QEMU_TLS_GCC_H
> +#define QEMU_TLS_GCC_H

Extra _GCC. But does no harm.

> +
> +/* Per-thread variables. Note that we only have implementations
> + * which are really thread-local on Linux; the dummy implementations
> + * define plain global variables.
> + *
> + * This means that for the moment use should be restricted to
> + * per-VCPU variables, which are OK because:
> + *  - the only -user mode supporting multiple VCPU threads is linux-user
> + *  - TCG system mode is single-threaded regarding VCPUs
> + *  - KVM system mode is multi-threaded but limited to Linux
> + *
> + * TODO: proper implementations via Win32 .tls sections and
> + * POSIX pthread_getspecific.
> + */
> +#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 which define plain global variables */
> +#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
> +
> +#endif

Looks okay to me.

I assume __typeof__() is a GCCism, indicated by ..._GCC_H, to ensure
type is actually a valid type?

Andreas

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