[PATCHv2] libstdc++: Mark pieces of gnu-linux/os_support.h linux-specific

[PATCHv2] libstdc++: Mark pieces of gnu-linux/os_support.h linux-specific

[Samuel Thibault]

This is notably needed because in glibc 2.34, the move of pthread functions
into libc.so happened for Linux only, not GNU/Hurd.

The pthread_self() function can also always be used fine as it is on
GNU/Hurd.

libstdc++-v3/ChangeLog:

        * config/os/gnu-linux/os_defines.h [!__linux__]
          (_GLIBCXX_NATIVE_THREAD_ID, _GLIBCXX_GTHREAD_USE_WEAK): Do not define.

diff --git a/libstdc++-v3/config/os/gnu-linux/os_defines.h b/libstdc++-v3/config/os/gnu-linux/os_defines.h
index c0caa21a013..4de93d752e1 100644
--- a/libstdc++-v3/config/os/gnu-linux/os_defines.h
+++ b/libstdc++-v3/config/os/gnu-linux/os_defines.h
@@ -49,22 +49,24 @@
 // version dynamically in case it has changed since libstdc++ was configured.
 #define _GLIBCXX_NO_OBSOLETE_ISINF_ISNAN_DYNAMIC __GLIBC_PREREQ(2,23)
 
-#if __GLIBC_PREREQ(2, 27)
-// Since glibc 2.27 pthread_self() is usable without linking to libpthread.
-# define _GLIBCXX_NATIVE_THREAD_ID pthread_self()
-#else
+#ifdef __linux__
+# if __GLIBC_PREREQ(2, 27)
+// Since glibc 2.27 Linux' pthread_self() is usable without linking to libpthread.
+#  define _GLIBCXX_NATIVE_THREAD_ID pthread_self()
+# else
 // Before then it was in libc.so.6 but not libc.a, and always returns 0,
 // which breaks the invariant this_thread::get_id() != thread::id{}.
 // So only use it if we know the libpthread version is available.
 // Otherwise use (__gthread_t)1 as the ID of the main (and only) thread.
-# define _GLIBCXX_NATIVE_THREAD_ID \
-  (__gthread_active_p() ? __gthread_self() : (__gthread_t)1)
-#endif
+#  define _GLIBCXX_NATIVE_THREAD_ID \
+   (__gthread_active_p() ? __gthread_self() : (__gthread_t)1)
+# endif
 
-#if __GLIBC_PREREQ(2, 34)
-// Since glibc 2.34 all pthreads functions are usable without linking to
+# if __GLIBC_PREREQ(2, 34)
+// Since glibc 2.34 all Linux pthreads functions are usable without linking to
 // libpthread.
-# define _GLIBCXX_GTHREAD_USE_WEAK 0
+#  define _GLIBCXX_GTHREAD_USE_WEAK 0
+# endif
 #endif
 
 #endif

Re: [PATCHv2] libstdc++: Mark pieces of gnu-linux/os_support.h linux-specific

[Jonathan Wakely]

On Fri, 7 Oct 2022 at 21:45, Samuel Thibault wrote:
>
> This is notably needed because in glibc 2.34, the move of pthread functions
> into libc.so happened for Linux only, not GNU/Hurd.
>
> The pthread_self() function can also always be used fine as it is on
> GNU/Hurd.

Sorry for the delay, I'm going to push this to trunk today.


>
> libstdc++-v3/ChangeLog:
>
>         * config/os/gnu-linux/os_defines.h [!__linux__]
>           (_GLIBCXX_NATIVE_THREAD_ID, _GLIBCXX_GTHREAD_USE_WEAK): Do not define.
>
> diff --git a/libstdc++-v3/config/os/gnu-linux/os_defines.h b/libstdc++-v3/config/os/gnu-linux/os_defines.h
> index c0caa21a013..4de93d752e1 100644
> --- a/libstdc++-v3/config/os/gnu-linux/os_defines.h
> +++ b/libstdc++-v3/config/os/gnu-linux/os_defines.h
> @@ -49,22 +49,24 @@
>  // version dynamically in case it has changed since libstdc++ was configured.
>  #define _GLIBCXX_NO_OBSOLETE_ISINF_ISNAN_DYNAMIC __GLIBC_PREREQ(2,23)
>
> -#if __GLIBC_PREREQ(2, 27)
> -// Since glibc 2.27 pthread_self() is usable without linking to libpthread.
> -# define _GLIBCXX_NATIVE_THREAD_ID pthread_self()
> -#else
> +#ifdef __linux__
> +# if __GLIBC_PREREQ(2, 27)
> +// Since glibc 2.27 Linux' pthread_self() is usable without linking to libpthread.
> +#  define _GLIBCXX_NATIVE_THREAD_ID pthread_self()
> +# else
>  // Before then it was in libc.so.6 but not libc.a, and always returns 0,
>  // which breaks the invariant this_thread::get_id() != thread::id{}.
>  // So only use it if we know the libpthread version is available.
>  // Otherwise use (__gthread_t)1 as the ID of the main (and only) thread.
> -# define _GLIBCXX_NATIVE_THREAD_ID \
> -  (__gthread_active_p() ? __gthread_self() : (__gthread_t)1)
> -#endif
> +#  define _GLIBCXX_NATIVE_THREAD_ID \
> +   (__gthread_active_p() ? __gthread_self() : (__gthread_t)1)
> +# endif
>
> -#if __GLIBC_PREREQ(2, 34)
> -// Since glibc 2.34 all pthreads functions are usable without linking to
> +# if __GLIBC_PREREQ(2, 34)
> +// Since glibc 2.34 all Linux pthreads functions are usable without linking to
>  // libpthread.
> -# define _GLIBCXX_GTHREAD_USE_WEAK 0
> +#  define _GLIBCXX_GTHREAD_USE_WEAK 0
> +# endif
>  #endif
>
>  #endif
>