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From: "sorear at fastmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug preprocessor/96952] New: __builtin_thread_pointer support
 cannot be probed
Date: Mon, 07 Sep 2020 11:25:55 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: preprocessor
X-Bugzilla-Version: 10.2.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96952

            Bug ID: 96952
           Summary: __builtin_thread_pointer support cannot be probed
           Product: gcc
           Version: 10.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: preprocessor
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sorear at fastmail dot com
  Target Milestone: ---

I would like to use __builtin_thread_pointer instead of inline asm to access
the thread pointer (concretely, in kernel or libc code for risc-v), but it's
only supported by extremely recent versions of gcc and clang.  So, I would =
like
to detect it at compile time, but this does not work:

#if __has_builtin(__builtin_thread_pointer)
void *get_tp() { return __builtin_thread_pointer(); }
#else
/* inline asm fallback */
#endif

x.c: In function 'get_tp':
x.c:2:25: error: '__builtin_thread_pointer' is not supported on this target
    2 | void *get_tp() { return __builtin_thread_pointer(); }
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~

__has_builtin seems to be falsely returning true?=