Re: [Qemu-devel] [PATCH] Make cpu_single_env thread local (Linux only for now)

[Lluís Vilanova]

Jan Kiszka writes:

> On 2011-10-03 18:33, Dr. David Alan Gilbert wrote:
>> Make cpu_single_env thread local (Linux only for now)
>> * Fixes some user space threading issues (esp those triggered
>> by bug 823902)
>> 
>> Against rev d11cf8cc..., tested on ARM user mode, and ARM Vexpress
>> system mode (with Blue Swirl's fix from yesterday) - only
>> tested on Linux host.  Lets me run ARM userspace firefox.
>> 
>> Signed-off-by: Dr. David Alan Gilbert <address@hidden>
>> 
>> diff --git a/cpu-all.h b/cpu-all.h
>> index 42a5fa0..d895ee6 100644
>> --- a/cpu-all.h
>> +++ b/cpu-all.h
>> @@ -334,7 +334,13 @@ void cpu_dump_statistics(CPUState *env, FILE *f, 
>> fprintf_function cpu_fprintf,
>> void QEMU_NORETURN cpu_abort(CPUState *env, const char *fmt, ...)
>> GCC_FMT_ATTR(2, 3);
>> extern CPUState *first_cpu;
>> +
>> +#ifdef __linux__
>> +/* DAG: Only tested thread local on Linux, feel free to add others */
>> +extern __thread CPUState *cpu_single_env;
>> +#else
>> extern CPUState *cpu_single_env;
>> +#endif

> We need this for all platforms in order to skip qemu_global_mutex while
> manipulating some CPUState. And leaving some platforms with non-TLS will
> eventually break them when code is added that assumes TLS.

> However, it's not unlikely that some weird platforms / ancient
> toolchains still have problems with __thread - even on Linux. We may
> want to play safe and use pthread_key on POSIX.

Why not make this kind of annotations available in qemu-commmon.h; or even
better somewhere less... "generic".

#if defined(CONFIG_SUPPORTS_THREAD_KEYWORD)

// use __thread
#define QEMU_DECL_TLS(type, name) \
        extern __thread type name;
#define QEMU_DEF_TLS(type, name) \
        __thread type name;
#define QEMU_SET_TLS(name, value) \
        do { name = value; } while (0)
#define QEMU_GET_TLS(name) \
        name

#elif defined(CONFIG_SUPPORTS_PTHREAD_KEY)

// use pthread_key_t
#define QEMU_DECL_TLS(type, name) \
        extern type _type_##name; \
        extern pthread_key_t name;
#define QEMU_DEF_TLS(type, name) \
        pthread_key_t name; \
        void _init_##name (void) __attribute__((constructor)); \
        void _init_##name (void) { pthread_key_create(&name, NULL); }
#define QEMU_SET_TLS(name, value) \
        do { pthread_setspecific(name, (void*)value); } while (0)
#define QEMU_GET_TLS(name) \
        ((typeof(_type_##name))pthread_getspecific(name))

#else
#error Go home
#endif


Lluis

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