Re: [Qemu-devel] [PATCH 2/2] qemu-thread: add TLS wrappers

[Peter Maydell]

On 1 July 2013 10:35, Stefan Hajnoczi <address@hidden> wrote:
> From: Paolo Bonzini <address@hidden>
>
> Fast TLS is not available on some platforms, but it is always nice to
> use it.  This wrapper implementation falls back to pthread_get/setspecific
> on POSIX systems that lack __thread, but uses the dynamic linker's TLS
> support on Linux and Windows.
>
> The user shall call tls_alloc_foo() in every thread that needs to access
> the variable---exactly once and before any access.  foo is the name of
> the variable as passed to DECLARE_TLS and DEFINE_TLS.  Then,
> tls_get_foo() will return the address of the variable.  It is guaranteed
> to remain the same across the lifetime of a thread, so you can cache it.

>  ##########################################
> +# check for TLS runtime
> +
> +# Some versions of mingw include the "magic" definitions that make
> +# TLS work, some don't.  Check for it.
> +
> +if test "$mingw32" = yes; then
> +  cat > $TMPC << EOF
> +int main(void) {}

Execution falls off the end of function without returning a value
(I would expect the compiler to issue a warning about this.)

> +#ifndef QEMU_TLS_H
> +#define QEMU_TLS_H
> +
> +#if defined __linux__
> +#define DECLARE_TLS(type, x)                     \
> +extern __thread typeof(type) x;                  \
> +                                                 \
> +static inline typeof(type) *tls_get_##x(void)    \
> +{                                                \
> +    return &x;                                   \
> +}                                                \
> +                                                 \
> +static inline typeof(type) *tls_alloc_##x(void)  \
> +{                                                \
> +    return &x;                                   \
> +}                                                \
> +                                                 \
> +extern int dummy_##__LINE__

What's this for?

thanks
-- PMM