Reduce <limits.h> pollution due to dynamic PTHREAD_STACK_MIN

<limits.h> used to be a header file with no declarations.
GCC's libgomp includes it in a #pragma GCC visibility hidden block.
Including <unistd.h> from <limits.h> (indirectly) declares everything
in <unistd.h> with hidden visibility, resulting in linker failures.

This commit avoids C declarations in assembler mode and only declares
__sysconf in <limits.h> (and not the entire contents of <unistd.h>).
The __sysconf symbol is already part of the ABI.  PTHREAD_STACK_MIN
is no longer defined for __USE_DYNAMIC_STACK_SIZE && __ASSEMBLER__
because there is no possible definition.

Additionally, PTHREAD_STACK_MIN is now defined by <pthread.h> for
__USE_MISC because this is what developers expect based on the macro
name.  It also helps to avoid libgomp linker failures in GCC because
libgomp includes <pthread.h> before its visibility hacks.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

2 files changed, 33 insertions, 8 deletions

diff --git a/sysdeps/unix/sysv/linux/bits/local_lim.h b/sysdeps/unix/sysv/linux/bits/local_lim.h
index 0b1c7f40be..b8f89236bc 100644
--- a/sysdeps/unix/sysv/linux/bits/local_lim.h
+++ b/sysdeps/unix/sysv/linux/bits/local_lim.h
@@ -77,14 +77,8 @@
    priority level.  */
 #define AIO_PRIO_DELTA_MAX	20
 
-/* Minimum size for a thread.  We are free to choose a reasonable value.  */
-#undef PTHREAD_STACK_MIN
-#if defined __USE_DYNAMIC_STACK_SIZE && __USE_DYNAMIC_STACK_SIZE
-# include <unistd.h>
-# define PTHREAD_STACK_MIN	sysconf (_SC_THREAD_STACK_MIN)
-#else
-# include <bits/pthread_stack_min.h>
-#endif
+/* Arrange for the definition of PTHREAD_STACK_MIN.  */
+#include <bits/pthread_stack_min-dynamic.h>
 
 /* Maximum number of timer expiration overruns.  */
 #define DELAYTIMER_MAX	2147483647
diff --git a/sysdeps/unix/sysv/linux/bits/pthread_stack_min-dynamic.h b/sysdeps/unix/sysv/linux/bits/pthread_stack_min-dynamic.h
new file mode 100644
index 0000000000..5f5fc5f024
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/bits/pthread_stack_min-dynamic.h
@@ -0,0 +1,31 @@
+/* Definition of PTHREAD_STACK_MIN, possibly dynamic.
+   Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef PTHREAD_STACK_MIN
+# if defined __USE_DYNAMIC_STACK_SIZE && __USE_DYNAMIC_STACK_SIZE
+#  ifndef __ASSEMBLER__
+#   define __SC_THREAD_STACK_MIN_VALUE 75
+__BEGIN_DECLS
+extern long int __sysconf (int __name) __THROW;
+__END_DECLS
+#   define PTHREAD_STACK_MIN __sysconf (__SC_THREAD_STACK_MIN_VALUE)
+#  endif
+# else
+#  include <bits/pthread_stack_min.h>
+# endif
+#endif